Stashed session keys

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Daniel Kahn Gillmor Daniel Kahn Gillmor
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Stashed session keys

Now that cleartext indexing is merged, let's add the ability to stash
session keys!

Background
==========

Encrypted e-mail messages are "hybrid" encryption.  The message body
is encrypted with an ephemeral session key, and then that session key
is itself encrypted to the user's public key.

If an MUA retains (or obtains) a copy of the session key for a given
message, it can access the cleartext of that message without needing
any access to the user's private key material.

This offers possible wins in efficiency, usability, convenience *and*
security, as the series hopefully makes clear.

Decryption Policies
===================

At the end of the series, there are four sensible policies defined for
message decryption and stashing of session keys.  There are only two i
expect to see any widespread regular use: "auto", and "true".  But
hopefully the reasons for including the other two policies ("false"
and "nostash") are made clear by the series itself.

I'll replicate here the table this series adds to notmuch-config(1),
in describing the available values for index.try_decrypt:

   +------------------------+-------+------+---------+------+
   |                        | false | auto | nostash | true |
   +========================+=======+======+=========+======+
   | Index cleartext using  |       |  X   |    X    |  X   |
   | stashed session keys   |       |      |         |      |
   +------------------------+-------+------+---------+------+
   | Index cleartext        |       |      |    X    |  X   |
   | using secret keys      |       |      |         |      |
   +------------------------+-------+------+---------+------+
   | Stash session keys     |       |      |         |  X   |
   +------------------------+-------+------+---------+------+
   | Delete stashed session |   X   |      |         |      |
   | keys on reindex        |       |      |         |      |
   +------------------------+-------+------+---------+------+


Please let me know what you think!  I'd love feedback and critique.

Happy hacking,

       --dkg

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[PATCH 01/18] mime-node: handle decrypt_result more safely

If (for whatever reason) we don't get a decrypt_result back, or it's
not structured the way we expect it to be, we shouldn't choke on it.
---
 mime-node.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/mime-node.c b/mime-node.c
index c3d5cb9b..28326e03 100644
--- a/mime-node.c
+++ b/mime-node.c
@@ -214,13 +214,15 @@ node_decrypt_and_verify (mime_node_t *node, GMimeObject *part,
     node->decrypt_success = true;
     node->verify_attempted = true;
 
-    /* This may be NULL if the part is not signed. */
-    node->sig_list = g_mime_decrypt_result_get_signatures (decrypt_result);
-    if (node->sig_list) {
- g_object_ref (node->sig_list);
- set_signature_list_destructor (node);
+    if (decrypt_result) {
+ /* This may be NULL if the part is not signed. */
+ node->sig_list = g_mime_decrypt_result_get_signatures (decrypt_result);
+ if (node->sig_list) {
+    g_object_ref (node->sig_list);
+    set_signature_list_destructor (node);
+ }
+ g_object_unref (decrypt_result);
     }
-    g_object_unref (decrypt_result);
 
  DONE:
     if (err)
--
2.14.2

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[PATCH 02/18] crypto: add _notmuch_crypto_decrypt wrapper function

In reply to this post by Daniel Kahn Gillmor
We will use this centralized function to consolidate the awkward
behavior around different gmime versions.

It's only invoked from two places: mime-node.c's
node_decrypt_and_verify() and lib/index.cc's
_index_encrypted_mime_part().

However, those two places have some markedly distinct logic, so the
interface for this _notmuch_crypto_decrypt function is going to get a
little bit clunky.  It's worthwhile, though, for the sake of keeping
these #if directives reasonably well-contained.
---
 lib/index.cc  |  8 ++------
 mime-node.c   |  8 ++------
 util/crypto.c | 18 ++++++++++++++++++
 util/crypto.h |  7 +++++--
 4 files changed, 27 insertions(+), 14 deletions(-)

diff --git a/lib/index.cc b/lib/index.cc
index 6e684f5f..19d03456 100644
--- a/lib/index.cc
+++ b/lib/index.cc
@@ -530,9 +530,9 @@ _index_encrypted_mime_part (notmuch_message_t *message,
 
     notmuch = _notmuch_message_database (message);
 
+    GMimeCryptoContext* crypto_ctx = NULL;
 #if (GMIME_MAJOR_VERSION < 3)
     {
- GMimeCryptoContext* crypto_ctx = NULL;
  const char *protocol = NULL;
  protocol = g_mime_content_type_get_parameter (content_type, "protocol");
  status = _notmuch_crypto_get_gmime_ctx_for_protocol (&(indexopts->crypto),
@@ -546,13 +546,9 @@ _index_encrypted_mime_part (notmuch_message_t *message,
       "property (%d)\n", status);
     return;
  }
- clear = g_mime_multipart_encrypted_decrypt(encrypted_data, crypto_ctx,
-   NULL, &err);
     }
-#else
-    clear = g_mime_multipart_encrypted_decrypt(encrypted_data, GMIME_DECRYPT_NONE, NULL,
-       NULL, &err);
 #endif
+    clear = _notmuch_crypto_decrypt (crypto_ctx, encrypted_data, NULL, &err);
     if (err) {
  _notmuch_database_log (notmuch, "Failed to decrypt during indexing. (%d:%d) [%s]\n",
        err->domain, err->code, err->message);
diff --git a/mime-node.c b/mime-node.c
index 28326e03..7f116531 100644
--- a/mime-node.c
+++ b/mime-node.c
@@ -199,12 +199,8 @@ node_decrypt_and_verify (mime_node_t *node, GMimeObject *part,
     GMimeMultipartEncrypted *encrypteddata = GMIME_MULTIPART_ENCRYPTED (part);
 
     node->decrypt_attempted = true;
-    node->decrypted_child = g_mime_multipart_encrypted_decrypt
-#if (GMIME_MAJOR_VERSION < 3)
- (encrypteddata, cryptoctx, &decrypt_result, &err);
-#else
-        (encrypteddata, GMIME_DECRYPT_NONE, NULL, &decrypt_result, &err);
-#endif
+    if (! node->decrypted_child)
+ node->decrypted_child = _notmuch_crypto_decrypt (cryptoctx, encrypteddata, &decrypt_result, &err);
     if (! node->decrypted_child) {
  fprintf (stderr, "Failed to decrypt part: %s\n",
  err ? err->message : "no error explanation given");
diff --git a/util/crypto.c b/util/crypto.c
index 5c84282e..087536ec 100644
--- a/util/crypto.c
+++ b/util/crypto.c
@@ -138,3 +138,21 @@ void _notmuch_crypto_cleanup (unused(_notmuch_crypto_t *crypto))
 {
 }
 #endif
+
+GMimeObject *
+_notmuch_crypto_decrypt (g_mime_3_unused(GMimeCryptoContext* crypto_ctx),
+ GMimeMultipartEncrypted *part,
+ GMimeDecryptResult **decrypt_result,
+ GError **err)
+{
+    GMimeObject *ret = NULL;
+
+#if (GMIME_MAJOR_VERSION < 3)
+    ret = g_mime_multipart_encrypted_decrypt(part, crypto_ctx,
+     decrypt_result, err);
+#else
+    ret = g_mime_multipart_encrypted_decrypt(part, GMIME_DECRYPT_NONE, NULL,
+     decrypt_result, err);
+#endif
+    return ret;
+}
diff --git a/util/crypto.h b/util/crypto.h
index 1ff0297d..d68634f3 100644
--- a/util/crypto.h
+++ b/util/crypto.h
@@ -2,10 +2,8 @@
 #define _CRYPTO_H
 
 #include <stdbool.h>
-#if (GMIME_MAJOR_VERSION < 3)
 #include "gmime-extra.h"
 #include "notmuch.h"
-#endif
 
 typedef struct _notmuch_crypto {
     bool verify;
@@ -17,6 +15,11 @@ typedef struct _notmuch_crypto {
 #endif
 } _notmuch_crypto_t;
 
+GMimeObject *
+_notmuch_crypto_decrypt (GMimeCryptoContext* crypto_ctx,
+ GMimeMultipartEncrypted *part,
+ GMimeDecryptResult **decrypt_result,
+ GError **err);
 
 #if (GMIME_MAJOR_VERSION < 3)
 notmuch_status_t
--
2.14.2

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[PATCH 03/18] crypto: use stashed session-key properties for decryption, if available

In reply to this post by Daniel Kahn Gillmor
When doing any decryption, if the notmuch database knows of any
session keys associated with the message in question, try them before
defaulting to using default symmetric crypto.

The primary advantage this offers is a significant speedup when
rendering large encrypted threads ("notmuch show") if session keys
happen to be cached.

Additionally, it permits message composition without access to
asymmetric secret keys ("notmuch reply"); and it permits recovering a
cleartext index when reindexing after a "notmuch restore" for those
messages that already have a session key stored.

This does nothing if no session keys are stashed in the database,
which is fine.  Actually stashing session keys in the database will
come as a subsequent patch.

Note that this only works for GMime 2.6.21 and later (the session key
interface wasn't available before then).  I don't think we're ready
for this to be a minimum version requirement yet, so instead if you
build against a prior version of GMime, it simply won't try to use
stashed session keys.
---
 doc/man7/notmuch-properties.rst | 31 +++++++++++++++++++++++++++++++
 lib/index.cc                    |  2 +-
 mime-node.c                     | 13 ++++++++++---
 util/crypto.c                   | 31 ++++++++++++++++++++++++++++++-
 util/crypto.h                   |  3 ++-
 5 files changed, 74 insertions(+), 6 deletions(-)

diff --git a/doc/man7/notmuch-properties.rst b/doc/man7/notmuch-properties.rst
index 68121359..31d7a104 100644
--- a/doc/man7/notmuch-properties.rst
+++ b/doc/man7/notmuch-properties.rst
@@ -74,6 +74,35 @@ of its normal activity.
     **notmuch-config(1)**), then this property will not be set on that
     message.
 
+**session-key**
+
+    When **notmuch-show(1)** or **nomtuch-reply** encounters a message
+    with an encrypted part and ``--decrypt`` is set, if notmuch finds a
+    ``session-key=`` property associated with the message, it will try
+    that stashed session key for decryption.
+
+    Using a stashed session key with "notmuch show" will speed up
+    rendering of long encrypted threads.  It also allows the user to
+    destroy the secret part of any expired encryption-capable subkey
+    while still being able to read any retained messages for which
+    they have stashed the session key.  This enables truly deletable
+    e-mail, since (once the session key and asymmetric subkey are both
+    destroyed) there are no keys left that can be used to decrypt any
+    copy of the original message previously stored by an adversary.
+
+    However, access to the stashed session key for an encrypted message
+    permits full byte-for-byte reconstruction of the cleartext
+    message.  This includes attachments, cryptographic signatures, and
+    other material that cannot be reconstructed from the index alone.
+
+    The session key should be in the ASCII text form produced by
+    GnuPG.  For OpenPGP, that consists of a decimal representation of
+    the hash algorithm used (identified by number from RFC 4880,
+    e.g. 9 means AES-256) followed by a colon, followed by a
+    hexidecimal representation of the algorithm-specific key.  For
+    example, an AES-128 key might be stashed in a notmuch property as:
+    ``session-key=7:14B16AF65536C28AF209828DFE34C9E0``.
+
 SEE ALSO
 ========
 
@@ -83,5 +112,7 @@ SEE ALSO
 **notmuch-insert(1)**,
 **notmuch-new(1)**,
 **notmuch-reindex(1)**,
+**notmuch-reply(1)**,
 **notmuch-restore(1)**,
+**notmuch-show(1)**,
 ***notmuch-search-terms(7)**
diff --git a/lib/index.cc b/lib/index.cc
index 19d03456..6eb60f30 100644
--- a/lib/index.cc
+++ b/lib/index.cc
@@ -548,7 +548,7 @@ _index_encrypted_mime_part (notmuch_message_t *message,
  }
     }
 #endif
-    clear = _notmuch_crypto_decrypt (crypto_ctx, encrypted_data, NULL, &err);
+    clear = _notmuch_crypto_decrypt (message, crypto_ctx, encrypted_data, NULL, &err);
     if (err) {
  _notmuch_database_log (notmuch, "Failed to decrypt during indexing. (%d:%d) [%s]\n",
        err->domain, err->code, err->message);
diff --git a/mime-node.c b/mime-node.c
index 7f116531..09170bfd 100644
--- a/mime-node.c
+++ b/mime-node.c
@@ -198,9 +198,16 @@ node_decrypt_and_verify (mime_node_t *node, GMimeObject *part,
     GMimeDecryptResult *decrypt_result = NULL;
     GMimeMultipartEncrypted *encrypteddata = GMIME_MULTIPART_ENCRYPTED (part);
 
-    node->decrypt_attempted = true;
-    if (! node->decrypted_child)
- node->decrypted_child = _notmuch_crypto_decrypt (cryptoctx, encrypteddata, &decrypt_result, &err);
+    if (! node->decrypted_child) {
+ mime_node_t *parent;
+ for (parent = node; parent; parent = parent->parent)
+    if (parent->envelope_file)
+ break;
+
+ node->decrypt_attempted = true;
+ node->decrypted_child = _notmuch_crypto_decrypt (parent ? parent->envelope_file : NULL,
+ cryptoctx, encrypteddata, &decrypt_result, &err);
+    }
     if (! node->decrypted_child) {
  fprintf (stderr, "Failed to decrypt part: %s\n",
  err ? err->message : "no error explanation given");
diff --git a/util/crypto.c b/util/crypto.c
index 087536ec..e014db5d 100644
--- a/util/crypto.c
+++ b/util/crypto.c
@@ -140,13 +140,42 @@ void _notmuch_crypto_cleanup (unused(_notmuch_crypto_t *crypto))
 #endif
 
 GMimeObject *
-_notmuch_crypto_decrypt (g_mime_3_unused(GMimeCryptoContext* crypto_ctx),
+_notmuch_crypto_decrypt (notmuch_message_t *message,
+ g_mime_3_unused(GMimeCryptoContext* crypto_ctx),
  GMimeMultipartEncrypted *part,
  GMimeDecryptResult **decrypt_result,
  GError **err)
 {
     GMimeObject *ret = NULL;
 
+    /* the versions of notmuch that can support session key decryption */
+#if (GMIME_MAJOR_VERSION >= 3 || (GMIME_MAJOR_VERSION == 2 && GMIME_MINOR_VERSION == 6 && GMIME_MICRO_VERSION >= 21))
+    if (message) {
+ notmuch_message_properties_t *list = NULL;
+
+ for (list = notmuch_message_get_properties (message, "session-key", TRUE);
+     notmuch_message_properties_valid (list); notmuch_message_properties_move_to_next (list)) {
+#if (GMIME_MAJOR_VERSION < 3)
+    ret = g_mime_multipart_encrypted_decrypt_session (part,
+      crypto_ctx,
+      notmuch_message_properties_value (list),
+      decrypt_result, err);
+#else
+    ret = g_mime_multipart_encrypted_decrypt (part,
+      GMIME_DECRYPT_NONE,
+      notmuch_message_properties_value (list),
+      decrypt_result, err);
+#endif
+    if (ret)
+ break;
+ }
+ if (list)
+    notmuch_message_properties_destroy (list);
+ if (ret)
+    return ret;
+    }
+#endif
+
 #if (GMIME_MAJOR_VERSION < 3)
     ret = g_mime_multipart_encrypted_decrypt(part, crypto_ctx,
      decrypt_result, err);
diff --git a/util/crypto.h b/util/crypto.h
index d68634f3..0c62ac70 100644
--- a/util/crypto.h
+++ b/util/crypto.h
@@ -16,7 +16,8 @@ typedef struct _notmuch_crypto {
 } _notmuch_crypto_t;
 
 GMimeObject *
-_notmuch_crypto_decrypt (GMimeCryptoContext* crypto_ctx,
+_notmuch_crypto_decrypt (notmuch_message_t *message,
+ GMimeCryptoContext* crypto_ctx,
  GMimeMultipartEncrypted *part,
  GMimeDecryptResult **decrypt_result,
  GError **err);
--
2.14.2

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[PATCH 04/18] test/corpora: add an encrypted message for index decryption tests

In reply to this post by Daniel Kahn Gillmor
---
 test/corpora/README                  |  5 +++++
 test/corpora/crypto/simple-encrypted | 36 ++++++++++++++++++++++++++++++++++++
 2 files changed, 41 insertions(+)
 create mode 100644 test/corpora/crypto/simple-encrypted

diff --git a/test/corpora/README b/test/corpora/README
index c9a35fed..05ea386d 100644
--- a/test/corpora/README
+++ b/test/corpora/README
@@ -12,3 +12,8 @@ broken
 
 html
   The html corpus contains html parts
+
+crypto
+  The crypto corpus contains encrypted messages for testing.
+  It should probably also contain signed messages in the future.
+  Please add them!
diff --git a/test/corpora/crypto/simple-encrypted b/test/corpora/crypto/simple-encrypted
new file mode 100644
index 00000000..6869972d
--- /dev/null
+++ b/test/corpora/crypto/simple-encrypted
@@ -0,0 +1,36 @@
+From: Daniel Kahn Gillmor <[hidden email]>
+To: [hidden email]
+Subject: encrypted message
+Date: Mon, 22 Dec 2016 08:34:56 -0400
+Message-ID: <[hidden email]>
+MIME-Version: 1.0
+Content-Type: multipart/encrypted; boundary="=-=-=";
+ protocol="application/pgp-encrypted"
+
+--=-=-=
+Content-Type: application/pgp-encrypted
+
+Version: 1
+
+--=-=-=
+Content-Type: application/octet-stream
+
+-----BEGIN PGP MESSAGE-----
+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+=frmz
+-----END PGP MESSAGE-----
+--=-=-=--
--
2.14.2

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[PATCH 05/18] crypto: Test restore of cleartext index from stashed session keys

In reply to this post by Daniel Kahn Gillmor
If you've got a notmuch dump that includes stashed session keys for
every decrypted message, and you've got your message archive, you
should be able to get back to the same index that you had before.

Here we add a simple test that give some flavor of how that works.
---
 test/T357-index-decryption.sh | 31 +++++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/test/T357-index-decryption.sh b/test/T357-index-decryption.sh
index 22e716c6..11ea2074 100755
--- a/test/T357-index-decryption.sh
+++ b/test/T357-index-decryption.sh
@@ -156,6 +156,37 @@ test_expect_equal \
     "$output" \
     "$expected"
 
+add_email_corpus crypto
+
+test_begin_subtest "indexing message fails when secret key not available"
+notmuch reindex --try-decrypt id:[hidden email]
+output=$(notmuch dump )
+expected='#notmuch-dump batch-tag:3 config,properties,tags
++encrypted +inbox +unread -- id:[hidden email]
+#= [hidden email] index.decryption=failure'
+test_expect_equal \
+    "$output" \
+    "$expected"
+
+test_begin_subtest "cannot find cleartext index"
+output=$(notmuch search sekrit)
+expected=''
+test_expect_equal \
+    "$output" \
+    "$expected"
+
+test_begin_subtest "cleartext index recovery on reindexing with stashed session keys"
+notmuch restore <<EOF
+#notmuch-dump batch-tag:3 config,properties,tags
+#= [hidden email] session-key=9%3AFC09987F5F927CC0CC0EE80A96E4C5BBF4A499818FB591207705DFDDD6112CF9
+EOF
+notmuch reindex --try-decrypt id:[hidden email]
+output=$(notmuch search sekrit)
+expected='thread:0000000000000001   2016-12-22 [1/1] Daniel Kahn Gillmor; encrypted message (encrypted inbox unread)'
+test_expect_equal \
+    "$output" \
+    "$expected"
+
 
 # TODO: test removal of a message from the message store between
 # indexing and reindexing.
--
2.14.2

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[PATCH 06/18] lib: convert notmuch decryption policy to an enum

In reply to this post by Daniel Kahn Gillmor
Future patches in this series will introduce new policies; this merely
readies the way for them.

We also convert --try-decrypt to a keyword argument instead of a boolean.
---
 lib/index.cc                  |  2 +-
 lib/indexopts.c               |  7 ++++---
 lib/notmuch.h                 | 14 ++++++++++++--
 mime-node.c                   |  4 ++--
 notmuch-client.h              |  9 +++++----
 notmuch-reply.c               |  6 +++++-
 notmuch-show.c                | 10 +++++++---
 notmuch.c                     | 13 ++++++++-----
 test/T357-index-decryption.sh | 12 ++++++------
 util/crypto.h                 |  2 +-
 10 files changed, 51 insertions(+), 28 deletions(-)

diff --git a/lib/index.cc b/lib/index.cc
index 6eb60f30..483fe31d 100644
--- a/lib/index.cc
+++ b/lib/index.cc
@@ -525,7 +525,7 @@ _index_encrypted_mime_part (notmuch_message_t *message,
     notmuch_database_t * notmuch = NULL;
     GMimeObject *clear = NULL;
 
-    if (!indexopts || !notmuch_indexopts_get_try_decrypt (indexopts))
+    if (!indexopts || (notmuch_indexopts_get_try_decrypt (indexopts) == NOTMUCH_DECRYPT_FALSE))
  return;
 
     notmuch = _notmuch_message_database (message);
diff --git a/lib/indexopts.c b/lib/indexopts.c
index 15c31d24..23557143 100644
--- a/lib/indexopts.c
+++ b/lib/indexopts.c
@@ -26,6 +26,7 @@ notmuch_database_get_default_indexopts (notmuch_database_t *db)
     notmuch_indexopts_t *ret = talloc_zero (db, notmuch_indexopts_t);
     if (!ret)
  return ret;
+    ret->crypto.decrypt = NOTMUCH_DECRYPT_FALSE;
 
     char * try_decrypt;
     notmuch_status_t err = notmuch_database_get_config (db, "index.try_decrypt", &try_decrypt);
@@ -36,7 +37,7 @@ notmuch_database_get_default_indexopts (notmuch_database_t *db)
  ((!(strcasecmp(try_decrypt, "true"))) ||
  (!(strcasecmp(try_decrypt, "yes"))) ||
  (!(strcasecmp(try_decrypt, "1")))))
- notmuch_indexopts_set_try_decrypt (ret, true);
+ notmuch_indexopts_set_try_decrypt (ret, NOTMUCH_DECRYPT_TRUE);
 
     free (try_decrypt);
     return ret;
@@ -44,7 +45,7 @@ notmuch_database_get_default_indexopts (notmuch_database_t *db)
 
 notmuch_status_t
 notmuch_indexopts_set_try_decrypt (notmuch_indexopts_t *indexopts,
-   notmuch_bool_t try_decrypt)
+   notmuch_decryption_policy_t try_decrypt)
 {
     if (!indexopts)
  return NOTMUCH_STATUS_NULL_POINTER;
@@ -52,7 +53,7 @@ notmuch_indexopts_set_try_decrypt (notmuch_indexopts_t *indexopts,
     return NOTMUCH_STATUS_SUCCESS;
 }
 
-notmuch_bool_t
+notmuch_decryption_policy_t
 notmuch_indexopts_get_try_decrypt (const notmuch_indexopts_t *indexopts)
 {
     if (!indexopts)
diff --git a/lib/notmuch.h b/lib/notmuch.h
index 2c5dcab5..26fe8f81 100644
--- a/lib/notmuch.h
+++ b/lib/notmuch.h
@@ -2233,6 +2233,16 @@ notmuch_config_list_destroy (notmuch_config_list_t *config_list);
 notmuch_indexopts_t *
 notmuch_database_get_default_indexopts (notmuch_database_t *db);
 
+/**
+ * Stating a policy about how to decrypt messages.
+ *
+ * See index.try_decrypt in notmuch-config(1) for more details.
+ */
+typedef enum {
+    NOTMUCH_DECRYPT_FALSE,
+    NOTMUCH_DECRYPT_TRUE,
+} notmuch_decryption_policy_t;
+
 /**
  * Specify whether to decrypt encrypted parts while indexing.
  *
@@ -2245,7 +2255,7 @@ notmuch_database_get_default_indexopts (notmuch_database_t *db);
  */
 notmuch_status_t
 notmuch_indexopts_set_try_decrypt (notmuch_indexopts_t *indexopts,
-   notmuch_bool_t try_decrypt);
+   notmuch_decryption_policy_t try_decrypt);
 
 /**
  * Return whether to decrypt encrypted parts while indexing.
@@ -2253,7 +2263,7 @@ notmuch_indexopts_set_try_decrypt (notmuch_indexopts_t *indexopts,
  *
  * @since libnotmuch 5.1 (notmuch 0.26)
  */
-notmuch_bool_t
+notmuch_decryption_policy_t
 notmuch_indexopts_get_try_decrypt (const notmuch_indexopts_t *indexopts);
 
 /**
diff --git a/mime-node.c b/mime-node.c
index 09170bfd..eb6a16c0 100644
--- a/mime-node.c
+++ b/mime-node.c
@@ -270,7 +270,7 @@ _mime_node_create (mime_node_t *parent, GMimeObject *part)
     }
 
 #if (GMIME_MAJOR_VERSION < 3)
-    if ((GMIME_IS_MULTIPART_ENCRYPTED (part) && node->ctx->crypto->decrypt)
+    if ((GMIME_IS_MULTIPART_ENCRYPTED (part) && (node->ctx->crypto->decrypt == NOTMUCH_DECRYPT_TRUE))
  || (GMIME_IS_MULTIPART_SIGNED (part) && node->ctx->crypto->verify)) {
  GMimeContentType *content_type = g_mime_object_get_content_type (part);
  const char *protocol = g_mime_content_type_get_parameter (content_type, "protocol");
@@ -286,7 +286,7 @@ _mime_node_create (mime_node_t *parent, GMimeObject *part)
 #endif
 
     /* Handle PGP/MIME parts */
-    if (GMIME_IS_MULTIPART_ENCRYPTED (part) && node->ctx->crypto->decrypt) {
+    if (GMIME_IS_MULTIPART_ENCRYPTED (part) && (node->ctx->crypto->decrypt == NOTMUCH_DECRYPT_TRUE)) {
  if (node->nchildren != 2) {
     /* this violates RFC 3156 section 4, so we won't bother with it. */
     fprintf (stderr, "Error: %d part(s) for a multipart/encrypted "
diff --git a/notmuch-client.h b/notmuch-client.h
index f7524e59..79b826c1 100644
--- a/notmuch-client.h
+++ b/notmuch-client.h
@@ -414,9 +414,10 @@ struct mime_node {
 
 /* Construct a new MIME node pointing to the root message part of
  * message. If crypto->verify is true, signed child parts will be
- * verified. If crypto->decrypt is true, encrypted child parts will be
- * decrypted.  If the crypto contexts (crypto->gpgctx or
- * crypto->pkcs7) are NULL, they will be lazily initialized.
+ * verified. If crypto->decrypt is NOTMUCH_DECRYPT_TRUE, encrypted
+ * child parts will be decrypted.  If the crypto contexts
+ * (crypto->gpgctx or crypto->pkcs7) are NULL, they will be lazily
+ * initialized.
  *
  * Return value:
  *
@@ -500,7 +501,7 @@ int notmuch_minimal_options (const char* subcommand_name,
 /* the state chosen by the user invoking one of the notmuch
  * subcommands that does indexing */
 struct _notmuch_client_indexing_cli_choices {
-    bool try_decrypt;
+    int try_decrypt;
     bool try_decrypt_set;
     notmuch_indexopts_t * opts;
 };
diff --git a/notmuch-reply.c b/notmuch-reply.c
index 2c7cc4eb..eec34bed 100644
--- a/notmuch-reply.c
+++ b/notmuch-reply.c
@@ -700,9 +700,11 @@ notmuch_reply_command (notmuch_config_t *config, int argc, char *argv[])
     int opt_index;
     notmuch_show_params_t params = {
  .part = -1,
+ .crypto = { .decrypt = NOTMUCH_DECRYPT_FALSE },
     };
     int format = FORMAT_DEFAULT;
     int reply_all = true;
+    bool decrypt = false;
 
     notmuch_opt_desc_t options[] = {
  { .opt_keyword = &format, .name = "format", .keywords =
@@ -716,7 +718,7 @@ notmuch_reply_command (notmuch_config_t *config, int argc, char *argv[])
   (notmuch_keyword_t []){ { "all", true },
   { "sender", false },
   { 0, 0 } } },
- { .opt_bool = &params.crypto.decrypt, .name = "decrypt" },
+ { .opt_bool = &decrypt, .name = "decrypt" },
  { .opt_inherit = notmuch_shared_options },
  { }
     };
@@ -726,6 +728,8 @@ notmuch_reply_command (notmuch_config_t *config, int argc, char *argv[])
  return EXIT_FAILURE;
 
     notmuch_process_shared_options (argv[0]);
+    if (decrypt)
+ params.crypto.decrypt = NOTMUCH_DECRYPT_TRUE;
 
     notmuch_exit_if_unsupported_format ();
 
diff --git a/notmuch-show.c b/notmuch-show.c
index 7afd3947..7ee9685a 100644
--- a/notmuch-show.c
+++ b/notmuch-show.c
@@ -1083,11 +1083,13 @@ notmuch_show_command (notmuch_config_t *config, int argc, char *argv[])
  .part = -1,
  .omit_excluded = true,
  .output_body = true,
+ .crypto = { .decrypt = NOTMUCH_DECRYPT_FALSE },
     };
     int format = NOTMUCH_FORMAT_NOT_SPECIFIED;
     bool exclude = true;
     bool entire_thread_set = false;
     bool single_message;
+    bool decrypt = false;
 
     notmuch_opt_desc_t options[] = {
  { .opt_keyword = &format, .name = "format", .keywords =
@@ -1102,7 +1104,7 @@ notmuch_show_command (notmuch_config_t *config, int argc, char *argv[])
  { .opt_bool = &params.entire_thread, .name = "entire-thread",
   .present = &entire_thread_set },
  { .opt_int = &params.part, .name = "part" },
- { .opt_bool = &params.crypto.decrypt, .name = "decrypt" },
+ { .opt_bool = &decrypt, .name = "decrypt" },
  { .opt_bool = &params.crypto.verify, .name = "verify" },
  { .opt_bool = &params.output_body, .name = "body" },
  { .opt_bool = &params.include_html, .name = "include-html" },
@@ -1116,9 +1118,11 @@ notmuch_show_command (notmuch_config_t *config, int argc, char *argv[])
 
     notmuch_process_shared_options (argv[0]);
 
-    /* decryption implies verification */
-    if (params.crypto.decrypt)
+    if (decrypt) {
+ params.crypto.decrypt = NOTMUCH_DECRYPT_TRUE;
+ /* decryption implies verification */
  params.crypto.verify = true;
+    }
 
     /* specifying a part implies single message display */
     single_message = params.part >= 0;
diff --git a/notmuch.c b/notmuch.c
index 539ac58c..1abd8288 100644
--- a/notmuch.c
+++ b/notmuch.c
@@ -99,8 +99,11 @@ int notmuch_minimal_options (const char *subcommand_name,
 
 struct _notmuch_client_indexing_cli_choices indexing_cli_choices = { };
 const notmuch_opt_desc_t  notmuch_shared_indexing_options [] = {
-    { .opt_bool = &indexing_cli_choices.try_decrypt,
-      .present = &indexing_cli_choices.try_decrypt_set,
+    { .opt_keyword = &indexing_cli_choices.try_decrypt,
+      .present = &indexing_cli_choices.try_decrypt_set, .keywords =
+      (notmuch_keyword_t []){ { "false", NOTMUCH_DECRYPT_FALSE },
+      { "true", NOTMUCH_DECRYPT_TRUE },
+      { 0, 0 } },
       .name = "try-decrypt" },
     { }
 };
@@ -117,15 +120,15 @@ notmuch_process_shared_indexing_options (notmuch_database_t *notmuch, g_mime_3_u
     return NOTMUCH_STATUS_OUT_OF_MEMORY;
  status = notmuch_indexopts_set_try_decrypt (indexing_cli_choices.opts, indexing_cli_choices.try_decrypt);
  if (status != NOTMUCH_STATUS_SUCCESS) {
-    fprintf (stderr, "Error: Failed to set try_decrypt to %s. (%s)\n",
-     indexing_cli_choices.try_decrypt ? "True" : "False", notmuch_status_to_string (status));
+    fprintf (stderr, "Error: Failed to set try_decrypt to %d. (%s)\n",
+     indexing_cli_choices.try_decrypt, notmuch_status_to_string (status));
     notmuch_indexopts_destroy (indexing_cli_choices.opts);
     indexing_cli_choices.opts = NULL;
     return status;
  }
     }
 #if (GMIME_MAJOR_VERSION < 3)
-    if (indexing_cli_choices.opts && notmuch_indexopts_get_try_decrypt (indexing_cli_choices.opts)) {
+    if (indexing_cli_choices.opts && notmuch_indexopts_get_try_decrypt (indexing_cli_choices.opts) == NOTMUCH_DECRYPT_TRUE) {
  const char* gpg_path = notmuch_config_get_crypto_gpg_path (config);
  if (gpg_path && strcmp(gpg_path, "gpg"))
     fprintf (stderr, "Warning: deprecated crypto.gpg_path is set to '%s'\n"
diff --git a/test/T357-index-decryption.sh b/test/T357-index-decryption.sh
index 11ea2074..670d1ae9 100755
--- a/test/T357-index-decryption.sh
+++ b/test/T357-index-decryption.sh
@@ -71,8 +71,8 @@ test_expect_equal \
 
 # try reinserting it with decryption, should appear again, but now we
 # have two copies of the message:
-test_begin_subtest "message cleartext is present after reinserting with --try-decrypt"
-notmuch insert --folder=sent --try-decrypt <<<"$contents"
+test_begin_subtest "message cleartext is present after reinserting with --try-decrypt=true"
+notmuch insert --folder=sent --try-decrypt=true <<<"$contents"
 output=$(notmuch search wumpus)
 expected='thread:0000000000000003   2000-01-01 [1/1(2)] Notmuch Test Suite; test encrypted message for cleartext index 002 (encrypted inbox unread)'
 test_expect_equal \
@@ -93,8 +93,8 @@ test_expect_equal \
 # try inserting it with decryption, should appear as a single copy
 # (note: i think thread id skips 4 because of duplicate message-id
 # insertion, above)
-test_begin_subtest "message cleartext is present with insert --try-decrypt"
-notmuch insert --folder=sent --try-decrypt <<<"$contents"
+test_begin_subtest "message cleartext is present with insert --try-decrypt=true"
+notmuch insert --folder=sent --try-decrypt=true <<<"$contents"
 output=$(notmuch search wumpus)
 expected='thread:0000000000000005   2000-01-01 [1/1] Notmuch Test Suite; test encrypted message for cleartext index 002 (encrypted inbox unread)'
 test_expect_equal \
@@ -159,7 +159,7 @@ test_expect_equal \
 add_email_corpus crypto
 
 test_begin_subtest "indexing message fails when secret key not available"
-notmuch reindex --try-decrypt id:[hidden email]
+notmuch reindex --try-decrypt=true id:[hidden email]
 output=$(notmuch dump )
 expected='#notmuch-dump batch-tag:3 config,properties,tags
 +encrypted +inbox +unread -- id:[hidden email]
@@ -180,7 +180,7 @@ notmuch restore <<EOF
 #notmuch-dump batch-tag:3 config,properties,tags
 #= [hidden email] session-key=9%3AFC09987F5F927CC0CC0EE80A96E4C5BBF4A499818FB591207705DFDDD6112CF9
 EOF
-notmuch reindex --try-decrypt id:[hidden email]
+notmuch reindex --try-decrypt=true id:[hidden email]
 output=$(notmuch search sekrit)
 expected='thread:0000000000000001   2016-12-22 [1/1] Daniel Kahn Gillmor; encrypted message (encrypted inbox unread)'
 test_expect_equal \
diff --git a/util/crypto.h b/util/crypto.h
index 0c62ac70..b23ca747 100644
--- a/util/crypto.h
+++ b/util/crypto.h
@@ -7,7 +7,7 @@
 
 typedef struct _notmuch_crypto {
     bool verify;
-    bool decrypt;
+    notmuch_decryption_policy_t decrypt;
 #if (GMIME_MAJOR_VERSION < 3)
     GMimeCryptoContext* gpgctx;
     GMimeCryptoContext* pkcs7ctx;
--
2.14.2

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Daniel Kahn Gillmor Daniel Kahn Gillmor
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[PATCH 07/18] crypto: new decryption policy "auto"

In reply to this post by Daniel Kahn Gillmor
This new automatic decryption policy should make it possible to
decrypt messages that we have stashed session keys for, without
incurring a call to the user's asymmetric keys.
---
 doc/man1/notmuch-config.rst   | 11 ++++++++---
 lib/index.cc                  |  3 ++-
 lib/indexopts.c               | 13 ++++++++-----
 lib/notmuch.h                 |  1 +
 mime-node.c                   |  7 ++++---
 notmuch-client.h              |  4 +++-
 notmuch.c                     |  3 ++-
 test/T357-index-decryption.sh | 12 +++++++++++-
 util/crypto.c                 |  8 +++++++-
 util/crypto.h                 |  3 ++-
 10 files changed, 48 insertions(+), 17 deletions(-)

diff --git a/doc/man1/notmuch-config.rst b/doc/man1/notmuch-config.rst
index 6961737f..14642062 100644
--- a/doc/man1/notmuch-config.rst
+++ b/doc/man1/notmuch-config.rst
@@ -142,9 +142,14 @@ The available configuration items are described below.
 
         **[STORED IN DATABASE]**
         When indexing an encrypted e-mail message, if this variable is
-        set to true, notmuch will try to decrypt the message and index
-        the cleartext.  Be aware that the index is likely sufficient
-        to reconstruct the cleartext of the message itself, so please
+        set to ``true``, notmuch will try to decrypt the message and
+        index the cleartext.  If ``auto``, it will try to index the
+        cleartext if a stashed session key is already known for the message,
+        but will not try to access your secret keys.  Use ``false`` to
+        avoid decrypting even when a session key is already known.
+
+        Be aware that the notmuch index is likely sufficient to
+        reconstruct the cleartext of the message itself, so please
         ensure that the notmuch message index is adequately protected.
         DO NOT USE ``index.try_decrypt=true`` without considering the
         security of your index.
diff --git a/lib/index.cc b/lib/index.cc
index 483fe31d..d9a0018c 100644
--- a/lib/index.cc
+++ b/lib/index.cc
@@ -548,7 +548,8 @@ _index_encrypted_mime_part (notmuch_message_t *message,
  }
     }
 #endif
-    clear = _notmuch_crypto_decrypt (message, crypto_ctx, encrypted_data, NULL, &err);
+    clear = _notmuch_crypto_decrypt (notmuch_indexopts_get_try_decrypt (indexopts),
+     message, crypto_ctx, encrypted_data, NULL, &err);
     if (err) {
  _notmuch_database_log (notmuch, "Failed to decrypt during indexing. (%d:%d) [%s]\n",
        err->domain, err->code, err->message);
diff --git a/lib/indexopts.c b/lib/indexopts.c
index 23557143..93a2c9eb 100644
--- a/lib/indexopts.c
+++ b/lib/indexopts.c
@@ -33,11 +33,14 @@ notmuch_database_get_default_indexopts (notmuch_database_t *db)
     if (err)
  return ret;
 
-    if (try_decrypt &&
- ((!(strcasecmp(try_decrypt, "true"))) ||
- (!(strcasecmp(try_decrypt, "yes"))) ||
- (!(strcasecmp(try_decrypt, "1")))))
- notmuch_indexopts_set_try_decrypt (ret, NOTMUCH_DECRYPT_TRUE);
+    if (try_decrypt) {
+ if ((!(strcasecmp(try_decrypt, "true"))) ||
+    (!(strcasecmp(try_decrypt, "yes"))) ||
+    (!(strcasecmp(try_decrypt, "1"))))
+    notmuch_indexopts_set_try_decrypt (ret, NOTMUCH_DECRYPT_TRUE);
+ else if (!strcasecmp(try_decrypt, "auto"))
+    notmuch_indexopts_set_try_decrypt (ret, NOTMUCH_DECRYPT_AUTO);
+    }
 
     free (try_decrypt);
     return ret;
diff --git a/lib/notmuch.h b/lib/notmuch.h
index 26fe8f81..7b1c61ad 100644
--- a/lib/notmuch.h
+++ b/lib/notmuch.h
@@ -2241,6 +2241,7 @@ notmuch_database_get_default_indexopts (notmuch_database_t *db);
 typedef enum {
     NOTMUCH_DECRYPT_FALSE,
     NOTMUCH_DECRYPT_TRUE,
+    NOTMUCH_DECRYPT_AUTO,
 } notmuch_decryption_policy_t;
 
 /**
diff --git a/mime-node.c b/mime-node.c
index eb6a16c0..815c1787 100644
--- a/mime-node.c
+++ b/mime-node.c
@@ -205,7 +205,8 @@ node_decrypt_and_verify (mime_node_t *node, GMimeObject *part,
  break;
 
  node->decrypt_attempted = true;
- node->decrypted_child = _notmuch_crypto_decrypt (parent ? parent->envelope_file : NULL,
+ node->decrypted_child = _notmuch_crypto_decrypt (node->ctx->crypto->decrypt,
+ parent ? parent->envelope_file : NULL,
  cryptoctx, encrypteddata, &decrypt_result, &err);
     }
     if (! node->decrypted_child) {
@@ -270,7 +271,7 @@ _mime_node_create (mime_node_t *parent, GMimeObject *part)
     }
 
 #if (GMIME_MAJOR_VERSION < 3)
-    if ((GMIME_IS_MULTIPART_ENCRYPTED (part) && (node->ctx->crypto->decrypt == NOTMUCH_DECRYPT_TRUE))
+    if ((GMIME_IS_MULTIPART_ENCRYPTED (part) && (node->ctx->crypto->decrypt != NOTMUCH_DECRYPT_FALSE))
  || (GMIME_IS_MULTIPART_SIGNED (part) && node->ctx->crypto->verify)) {
  GMimeContentType *content_type = g_mime_object_get_content_type (part);
  const char *protocol = g_mime_content_type_get_parameter (content_type, "protocol");
@@ -286,7 +287,7 @@ _mime_node_create (mime_node_t *parent, GMimeObject *part)
 #endif
 
     /* Handle PGP/MIME parts */
-    if (GMIME_IS_MULTIPART_ENCRYPTED (part) && (node->ctx->crypto->decrypt == NOTMUCH_DECRYPT_TRUE)) {
+    if (GMIME_IS_MULTIPART_ENCRYPTED (part) && (node->ctx->crypto->decrypt != NOTMUCH_DECRYPT_FALSE)) {
  if (node->nchildren != 2) {
     /* this violates RFC 3156 section 4, so we won't bother with it. */
     fprintf (stderr, "Error: %d part(s) for a multipart/encrypted "
diff --git a/notmuch-client.h b/notmuch-client.h
index 79b826c1..6aec9974 100644
--- a/notmuch-client.h
+++ b/notmuch-client.h
@@ -415,7 +415,9 @@ struct mime_node {
 /* Construct a new MIME node pointing to the root message part of
  * message. If crypto->verify is true, signed child parts will be
  * verified. If crypto->decrypt is NOTMUCH_DECRYPT_TRUE, encrypted
- * child parts will be decrypted.  If the crypto contexts
+ * child parts will be decrypted using either stored session keys or
+ * asymmetric crypto.  If crypto->decrypt is NOTMUCH_DECRYPT_AUTO,
+ * only session keys will be tried.  If the crypto contexts
  * (crypto->gpgctx or crypto->pkcs7) are NULL, they will be lazily
  * initialized.
  *
diff --git a/notmuch.c b/notmuch.c
index 1abd8288..62706748 100644
--- a/notmuch.c
+++ b/notmuch.c
@@ -103,6 +103,7 @@ const notmuch_opt_desc_t  notmuch_shared_indexing_options [] = {
       .present = &indexing_cli_choices.try_decrypt_set, .keywords =
       (notmuch_keyword_t []){ { "false", NOTMUCH_DECRYPT_FALSE },
       { "true", NOTMUCH_DECRYPT_TRUE },
+      { "auto", NOTMUCH_DECRYPT_AUTO },
       { 0, 0 } },
       .name = "try-decrypt" },
     { }
@@ -128,7 +129,7 @@ notmuch_process_shared_indexing_options (notmuch_database_t *notmuch, g_mime_3_u
  }
     }
 #if (GMIME_MAJOR_VERSION < 3)
-    if (indexing_cli_choices.opts && notmuch_indexopts_get_try_decrypt (indexing_cli_choices.opts) == NOTMUCH_DECRYPT_TRUE) {
+    if (indexing_cli_choices.opts && notmuch_indexopts_get_try_decrypt (indexing_cli_choices.opts) != NOTMUCH_DECRYPT_FALSE) {
  const char* gpg_path = notmuch_config_get_crypto_gpg_path (config);
  if (gpg_path && strcmp(gpg_path, "gpg"))
     fprintf (stderr, "Warning: deprecated crypto.gpg_path is set to '%s'\n"
diff --git a/test/T357-index-decryption.sh b/test/T357-index-decryption.sh
index 670d1ae9..d453d568 100755
--- a/test/T357-index-decryption.sh
+++ b/test/T357-index-decryption.sh
@@ -140,6 +140,16 @@ test_expect_equal \
     "$output" \
     "$expected"
 
+# ensure no session keys are present:
+test_begin_subtest 'reindex using only session keys'
+test_expect_success 'notmuch reindex --try-decrypt=auto tag:encrypted and property:index.decryption=success'
+test_begin_subtest "reindexed encrypted messages, decrypting only with session keys"
+output=$(notmuch search wumpus)
+expected=''
+test_expect_equal \
+    "$output" \
+    "$expected"
+
 # and the same search, but by property ($expected is untouched):
 test_begin_subtest "emacs search by property with both messages unindexed"
 output=$(notmuch search property:index.decryption=success)
@@ -180,7 +190,7 @@ notmuch restore <<EOF
 #notmuch-dump batch-tag:3 config,properties,tags
 #= [hidden email] session-key=9%3AFC09987F5F927CC0CC0EE80A96E4C5BBF4A499818FB591207705DFDDD6112CF9
 EOF
-notmuch reindex --try-decrypt=true id:[hidden email]
+notmuch reindex --try-decrypt=auto id:[hidden email]
 output=$(notmuch search sekrit)
 expected='thread:0000000000000001   2016-12-22 [1/1] Daniel Kahn Gillmor; encrypted message (encrypted inbox unread)'
 test_expect_equal \
diff --git a/util/crypto.c b/util/crypto.c
index e014db5d..9789f203 100644
--- a/util/crypto.c
+++ b/util/crypto.c
@@ -140,13 +140,16 @@ void _notmuch_crypto_cleanup (unused(_notmuch_crypto_t *crypto))
 #endif
 
 GMimeObject *
-_notmuch_crypto_decrypt (notmuch_message_t *message,
+_notmuch_crypto_decrypt (notmuch_decryption_policy_t decrypt,
+ notmuch_message_t *message,
  g_mime_3_unused(GMimeCryptoContext* crypto_ctx),
  GMimeMultipartEncrypted *part,
  GMimeDecryptResult **decrypt_result,
  GError **err)
 {
     GMimeObject *ret = NULL;
+    if (decrypt == NOTMUCH_DECRYPT_FALSE)
+ return NULL;
 
     /* the versions of notmuch that can support session key decryption */
 #if (GMIME_MAJOR_VERSION >= 3 || (GMIME_MAJOR_VERSION == 2 && GMIME_MINOR_VERSION == 6 && GMIME_MICRO_VERSION >= 21))
@@ -176,6 +179,9 @@ _notmuch_crypto_decrypt (notmuch_message_t *message,
     }
 #endif
 
+    if (decrypt == NOTMUCH_DECRYPT_AUTO)
+ return ret;
+
 #if (GMIME_MAJOR_VERSION < 3)
     ret = g_mime_multipart_encrypted_decrypt(part, crypto_ctx,
      decrypt_result, err);
diff --git a/util/crypto.h b/util/crypto.h
index b23ca747..dc95b4ca 100644
--- a/util/crypto.h
+++ b/util/crypto.h
@@ -16,7 +16,8 @@ typedef struct _notmuch_crypto {
 } _notmuch_crypto_t;
 
 GMimeObject *
-_notmuch_crypto_decrypt (notmuch_message_t *message,
+_notmuch_crypto_decrypt (notmuch_decryption_policy_t decrypt,
+ notmuch_message_t *message,
  GMimeCryptoContext* crypto_ctx,
  GMimeMultipartEncrypted *part,
  GMimeDecryptResult **decrypt_result,
--
2.14.2

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[PATCH 08/18] cli/reply: use decryption policy "auto" by default.

In reply to this post by Daniel Kahn Gillmor
If the user doesn't specify --decrypt= at all, but a stashed session
key is known to notmuch, when replying to an encrypted message,
notmuch should just go ahead and decrypt.

The user can disable this at the command line with --decrypt=false,
though it's not clear why they would ever want to do that.
---
 completion/notmuch-completion.bash | 6 +++++-
 doc/man1/notmuch-reply.rst         | 6 +++++-
 notmuch-reply.c                    | 9 +++++----
 test/T357-index-decryption.sh      | 7 +++++++
 4 files changed, 22 insertions(+), 6 deletions(-)

diff --git a/completion/notmuch-completion.bash b/completion/notmuch-completion.bash
index 7aae4297..5e408b9d 100644
--- a/completion/notmuch-completion.bash
+++ b/completion/notmuch-completion.bash
@@ -350,12 +350,16 @@ _notmuch_reply()
     COMPREPLY=( $( compgen -W "all sender" -- "${cur}" ) )
     return
     ;;
+ --decrypt)
+    COMPREPLY=( $( compgen -W "true false" -- "${cur}" ) )
+    return
+    ;;
     esac
 
     ! $split &&
     case "${cur}" in
  -*)
-    local options="--format= --format-version= --reply-to= --decrypt ${_notmuch_shared_options}"
+    local options="--format= --format-version= --reply-to= --decrypt= ${_notmuch_shared_options}"
     compopt -o nospace
     COMPREPLY=( $(compgen -W "$options" -- ${cur}) )
     ;;
diff --git a/doc/man1/notmuch-reply.rst b/doc/man1/notmuch-reply.rst
index b6aec3c8..ede77930 100644
--- a/doc/man1/notmuch-reply.rst
+++ b/doc/man1/notmuch-reply.rst
@@ -80,8 +80,12 @@ Supported options for **reply** include
         multipart/encrypted part will be replaced by the decrypted
         content.
 
+        If a session key is already known for the message, then it
+        will be decrypted automatically unless the user explicitly
+        sets ``--decrypt=false``.
+
         Decryption expects a functioning **gpg-agent(1)** to provide any
-        needed credentials. Without one, the decryption will fail.
+        needed credentials. Without one, the decryption will likely fail.
 
 See **notmuch-search-terms(7)** for details of the supported syntax for
 <search-terms>.
diff --git a/notmuch-reply.c b/notmuch-reply.c
index eec34bed..fd990a9a 100644
--- a/notmuch-reply.c
+++ b/notmuch-reply.c
@@ -700,11 +700,12 @@ notmuch_reply_command (notmuch_config_t *config, int argc, char *argv[])
     int opt_index;
     notmuch_show_params_t params = {
  .part = -1,
- .crypto = { .decrypt = NOTMUCH_DECRYPT_FALSE },
+ .crypto = { .decrypt = NOTMUCH_DECRYPT_AUTO },
     };
     int format = FORMAT_DEFAULT;
     int reply_all = true;
     bool decrypt = false;
+    bool decrypt_set = false;
 
     notmuch_opt_desc_t options[] = {
  { .opt_keyword = &format, .name = "format", .keywords =
@@ -718,7 +719,7 @@ notmuch_reply_command (notmuch_config_t *config, int argc, char *argv[])
   (notmuch_keyword_t []){ { "all", true },
   { "sender", false },
   { 0, 0 } } },
- { .opt_bool = &decrypt, .name = "decrypt" },
+ { .opt_bool = &decrypt, .name = "decrypt", .present = &decrypt_set },
  { .opt_inherit = notmuch_shared_options },
  { }
     };
@@ -728,8 +729,8 @@ notmuch_reply_command (notmuch_config_t *config, int argc, char *argv[])
  return EXIT_FAILURE;
 
     notmuch_process_shared_options (argv[0]);
-    if (decrypt)
- params.crypto.decrypt = NOTMUCH_DECRYPT_TRUE;
+    if (decrypt_set)
+ params.crypto.decrypt = decrypt ? NOTMUCH_DECRYPT_TRUE : NOTMUCH_DECRYPT_FALSE;
 
     notmuch_exit_if_unsupported_format ();
 
diff --git a/test/T357-index-decryption.sh b/test/T357-index-decryption.sh
index d453d568..61360e42 100755
--- a/test/T357-index-decryption.sh
+++ b/test/T357-index-decryption.sh
@@ -197,6 +197,13 @@ test_expect_equal \
     "$output" \
     "$expected"
 
+test_begin_subtest "notmuch reply should show cleartext if session key is present"
+output=$(notmuch reply id:[hidden email] | grep '^>')
+expected='> This is a top sekrit message.'
+test_expect_equal \
+    "$output" \
+    "$expected"
+
 
 # TODO: test removal of a message from the message store between
 # indexing and reindexing.
--
2.14.2

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[PATCH 09/18] cli/show: use decryption policy "auto" by default.

In reply to this post by Daniel Kahn Gillmor
When showing a message, if the user doesn't specify --decrypt= at all,
but a stashed session key is known to notmuch, notmuch should just go
ahead and try to decrypt the message with the session key (without
bothering the user for access to their asymmetric secret key).

The user can disable this at the command line with --decrypt=false if
they really don't want to look at the e-mail that they've asked
notmuch to show them.

and of course, "notmuch show --decrypt" still works for accessing the
user's secret keys if necessary.
---
 completion/notmuch-completion.bash |  4 ++--
 doc/man1/notmuch-show.rst          |  4 ++++
 notmuch-show.c                     | 17 +++++++++++------
 test/T357-index-decryption.sh      | 14 ++++++++++++++
 4 files changed, 31 insertions(+), 8 deletions(-)

diff --git a/completion/notmuch-completion.bash b/completion/notmuch-completion.bash
index 5e408b9d..2703d542 100644
--- a/completion/notmuch-completion.bash
+++ b/completion/notmuch-completion.bash
@@ -517,7 +517,7 @@ _notmuch_show()
     COMPREPLY=( $( compgen -W "text json sexp mbox raw" -- "${cur}" ) )
     return
     ;;
- --exclude|--body)
+ --exclude|--body|--decrypt)
     COMPREPLY=( $( compgen -W "true false" -- "${cur}" ) )
     return
     ;;
@@ -526,7 +526,7 @@ _notmuch_show()
     ! $split &&
     case "${cur}" in
  -*)
-    local options="--entire-thread= --format= --exclude= --body= --format-version= --part= --verify --decrypt --include-html ${_notmuch_shared_options}"
+    local options="--entire-thread= --format= --exclude= --body= --format-version= --part= --verify --decrypt= --include-html ${_notmuch_shared_options}"
     compopt -o nospace
     COMPREPLY=( $(compgen -W "$options" -- ${cur}) )
     ;;
diff --git a/doc/man1/notmuch-show.rst b/doc/man1/notmuch-show.rst
index 7ba091cf..64caa7a6 100644
--- a/doc/man1/notmuch-show.rst
+++ b/doc/man1/notmuch-show.rst
@@ -123,6 +123,10 @@ Supported options for **show** include
         multipart/encrypted part will be replaced by the decrypted
         content.
 
+        If a session key is already known for the message, then it
+        will be decrypted automatically unless the user explicitly
+        sets ``--decrypt=false``.
+
         Decryption expects a functioning **gpg-agent(1)** to provide any
         needed credentials. Without one, the decryption will fail.
 
diff --git a/notmuch-show.c b/notmuch-show.c
index 7ee9685a..c8f5a48f 100644
--- a/notmuch-show.c
+++ b/notmuch-show.c
@@ -1083,13 +1083,14 @@ notmuch_show_command (notmuch_config_t *config, int argc, char *argv[])
  .part = -1,
  .omit_excluded = true,
  .output_body = true,
- .crypto = { .decrypt = NOTMUCH_DECRYPT_FALSE },
+ .crypto = { .decrypt = NOTMUCH_DECRYPT_AUTO },
     };
     int format = NOTMUCH_FORMAT_NOT_SPECIFIED;
     bool exclude = true;
     bool entire_thread_set = false;
     bool single_message;
     bool decrypt = false;
+    bool decrypt_set = false;
 
     notmuch_opt_desc_t options[] = {
  { .opt_keyword = &format, .name = "format", .keywords =
@@ -1104,7 +1105,7 @@ notmuch_show_command (notmuch_config_t *config, int argc, char *argv[])
  { .opt_bool = &params.entire_thread, .name = "entire-thread",
   .present = &entire_thread_set },
  { .opt_int = &params.part, .name = "part" },
- { .opt_bool = &decrypt, .name = "decrypt" },
+ { .opt_bool = &decrypt, .name = "decrypt", .present = &decrypt_set },
  { .opt_bool = &params.crypto.verify, .name = "verify" },
  { .opt_bool = &params.output_body, .name = "body" },
  { .opt_bool = &params.include_html, .name = "include-html" },
@@ -1118,10 +1119,14 @@ notmuch_show_command (notmuch_config_t *config, int argc, char *argv[])
 
     notmuch_process_shared_options (argv[0]);
 
-    if (decrypt) {
- params.crypto.decrypt = NOTMUCH_DECRYPT_TRUE;
- /* decryption implies verification */
- params.crypto.verify = true;
+    if (decrypt_set) {
+ if (decrypt) {
+    params.crypto.decrypt = NOTMUCH_DECRYPT_TRUE;
+    /* decryption implies verification */
+    params.crypto.verify = true;
+ } else {
+    params.crypto.decrypt = NOTMUCH_DECRYPT_FALSE;
+ }
     }
 
     /* specifying a part implies single message display */
diff --git a/test/T357-index-decryption.sh b/test/T357-index-decryption.sh
index 61360e42..30bdf704 100755
--- a/test/T357-index-decryption.sh
+++ b/test/T357-index-decryption.sh
@@ -204,6 +204,20 @@ test_expect_equal \
     "$output" \
     "$expected"
 
+test_begin_subtest "notmuch show should show cleartext if session key is present"
+output=$(notmuch show id:[hidden email] | awk '/^\014part}/{ f=0 }; { if (f) { print $0 } } /^\014part{ ID: 3/{ f=1 }')
+expected='This is a top sekrit message.'
+test_expect_equal \
+    "$output" \
+    "$expected"
+
+test_begin_subtest "notmuch show should show nothing if decryption is explicitly disallowed"
+output=$(notmuch show --decrypt=false id:[hidden email] | awk '/^\014part}/{ f=0 }; { if (f) { print $0 } } /^\014part{ ID: 3/{ f=1 }')
+expected='Non-text part: application/octet-stream'
+test_expect_equal \
+    "$output" \
+    "$expected"
+
 
 # TODO: test removal of a message from the message store between
 # indexing and reindexing.
--
2.14.2

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[PATCH 10/18] cli/show, reply: document use of stashed session keys in notmuch-properties

In reply to this post by Daniel Kahn Gillmor
The stashed session keys are stored internally as notmuch properties.
So a user or developer who is reading about those properties might
want to understand how they fit into the bigger picture.

Note here that decrypting with a stored session key no longer needs
-decrypt for "notmuch show" and "notmuch reply".
---
 doc/man7/notmuch-properties.rst | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/doc/man7/notmuch-properties.rst b/doc/man7/notmuch-properties.rst
index 31d7a104..e2ab43be 100644
--- a/doc/man7/notmuch-properties.rst
+++ b/doc/man7/notmuch-properties.rst
@@ -77,9 +77,12 @@ of its normal activity.
 **session-key**
 
     When **notmuch-show(1)** or **nomtuch-reply** encounters a message
-    with an encrypted part and ``--decrypt`` is set, if notmuch finds a
-    ``session-key=`` property associated with the message, it will try
-    that stashed session key for decryption.
+    with an encrypted part, if notmuch finds a ``session-key=``
+    property associated with the message, it will try that stashed
+    session key for decryption.
+
+    If you do not want to use any stashed session keys that might be
+    present, you should pass those programs ``--decrypt=false``.
 
     Using a stashed session key with "notmuch show" will speed up
     rendering of long encrypted threads.  It also allows the user to
--
2.14.2

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[PATCH 11/18] cli/new, insert, reindex: update documentation for --try-decrypt=auto

In reply to this post by Daniel Kahn Gillmor
we also include --try-decrypt=auto in the tab completion.
---
 completion/notmuch-completion.bash |  6 +++---
 doc/man1/notmuch-insert.rst        | 16 ++++++++++------
 doc/man1/notmuch-new.rst           | 10 +++++++---
 doc/man1/notmuch-reindex.rst       | 23 ++++++++++++++---------
 4 files changed, 34 insertions(+), 21 deletions(-)

diff --git a/completion/notmuch-completion.bash b/completion/notmuch-completion.bash
index 2703d542..53d7380b 100644
--- a/completion/notmuch-completion.bash
+++ b/completion/notmuch-completion.bash
@@ -288,7 +288,7 @@ _notmuch_insert()
     return
     ;;
  --try-decrypt)
-    COMPREPLY=( $( compgen -W "true false" -- "${cur}" ) )
+    COMPREPLY=( $( compgen -W "true false auto" -- "${cur}" ) )
     return
     ;;
     esac
@@ -320,7 +320,7 @@ _notmuch_new()
     $split &&
     case "${prev}" in
  --try-decrypt)
-    COMPREPLY=( $( compgen -W "true false" -- "${cur}" ) )
+    COMPREPLY=( $( compgen -W "true false auto" -- "${cur}" ) )
     return
     ;;
     esac
@@ -442,7 +442,7 @@ _notmuch_reindex()
     $split &&
     case "${prev}" in
  --try-decrypt)
-    COMPREPLY=( $( compgen -W "true false" -- "${cur}" ) )
+    COMPREPLY=( $( compgen -W "true false auto" -- "${cur}" ) )
     return
     ;;
     esac
diff --git a/doc/man1/notmuch-insert.rst b/doc/man1/notmuch-insert.rst
index e2bf37d0..a5505b5b 100644
--- a/doc/man1/notmuch-insert.rst
+++ b/doc/man1/notmuch-insert.rst
@@ -50,14 +50,18 @@ Supported options for **insert** include
     ``--no-hooks``
         Prevent hooks from being run.
 
-    ``--try-decrypt=(true|false)``
+    ``--try-decrypt=(true|auto|false)``
 
-        If true and the message is encrypted, try to decrypt the
-        message while indexing.  If decryption is successful, index
+        If ``true`` and the message is encrypted, try to decrypt the
+        message while indexing.  If ``auto``, and notmuch already
+        knows about a session key for the message, it will try
+        decrypting using that session key but will not try to access
+        the user's secret keys.  If decryption is successful, index
         the cleartext itself.  Either way, the message is always
-        stored to disk in its original form (ciphertext).  Be aware
-        that the index is likely sufficient to reconstruct the
-        cleartext of the message itself, so please ensure that the
+        stored to disk in its original form (ciphertext).
+
+        Be aware that the index is likely sufficient to reconstruct
+        the cleartext of the message itself, so please ensure that the
         notmuch message index is adequately protected. DO NOT USE
         ``--try-decrypt=true`` without considering the security of
         your index.
diff --git a/doc/man1/notmuch-new.rst b/doc/man1/notmuch-new.rst
index bc26aa48..d8cb77f5 100644
--- a/doc/man1/notmuch-new.rst
+++ b/doc/man1/notmuch-new.rst
@@ -43,11 +43,15 @@ Supported options for **new** include
     ``--quiet``
         Do not print progress or results.
 
-    ``--try-decrypt=(true|false)``
+    ``--try-decrypt=(true|auto|false)``
 
-        If true, when encountering an encrypted message, try to
+        If ``true``, when encountering an encrypted message, try to
         decrypt it while indexing.  If decryption is successful, index
-        the cleartext itself.  Be aware that the index is likely
+        the cleartext itself.  If ``auto``, try to use any session key
+        already known to belong to this message, but do not attempt to
+        use the user's secret keys.
+
+        Be aware that the index is likely
         sufficient to reconstruct the cleartext of the message itself,
         so please ensure that the notmuch message index is adequately
         protected.  DO NOT USE ``--try-decrypt=true`` without
diff --git a/doc/man1/notmuch-reindex.rst b/doc/man1/notmuch-reindex.rst
index 21f6c7a9..b15981a2 100644
--- a/doc/man1/notmuch-reindex.rst
+++ b/doc/man1/notmuch-reindex.rst
@@ -21,15 +21,20 @@ messages using the supplied options.
 
 Supported options for **reindex** include
 
-    ``--try-decrypt=(true|false)``
-
-        If true, when encountering an encrypted message, try to
-        decrypt it while reindexing.  If decryption is successful,
-        index the cleartext itself.  Be aware that the index is likely
-        sufficient to reconstruct the cleartext of the message itself,
-        so please ensure that the notmuch message index is adequately
-        protected. DO NOT USE ``--try-decrypt=true`` without
-        considering the security of your index.
+    ``--try-decrypt=(true|auto|false)``
+
+        If ``true``, when encountering an encrypted message, try to
+        decrypt it while reindexing.  If ``auto``, and notmuch already
+        knows about a session key for the message, it will try
+        decrypting using that session key but will not try to access
+        the user's secret keys.  If decryption is successful, index
+        the cleartext itself.
+
+        Be aware that the index is likely sufficient to reconstruct
+        the cleartext of the message itself, so please ensure that the
+        notmuch message index is adequately protected. DO NOT USE
+        ``--try-decrypt=true`` without considering the security of
+        your index.
 
         See also ``index.try_decrypt`` in **notmuch-config(1)**.
 
--
2.14.2

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[PATCH 12/18] crypto: record whether an actual decryption attempt happened

In reply to this post by Daniel Kahn Gillmor
In our consolidation of _notmuch_crypto_decrypt, the callers lost
track a little bit of whether any actual decryption was attempted.

Now that we have the more-subtle "auto" policy, it's possible that
_notmuch_crypto_decrypt could be called without having any actual
decryption take place.

This change lets the callers be a little bit smarter about whether or
not any decryption was actually attempted.
---
 lib/index.cc  | 17 ++++++++++++-----
 mime-node.c   |  4 ++--
 util/crypto.c |  7 ++++++-
 util/crypto.h |  3 ++-
 4 files changed, 22 insertions(+), 9 deletions(-)

diff --git a/lib/index.cc b/lib/index.cc
index d9a0018c..e2701755 100644
--- a/lib/index.cc
+++ b/lib/index.cc
@@ -548,12 +548,19 @@ _index_encrypted_mime_part (notmuch_message_t *message,
  }
     }
 #endif
-    clear = _notmuch_crypto_decrypt (notmuch_indexopts_get_try_decrypt (indexopts),
+    bool attempted = false;
+    clear = _notmuch_crypto_decrypt (&attempted, notmuch_indexopts_get_try_decrypt (indexopts),
      message, crypto_ctx, encrypted_data, NULL, &err);
-    if (err) {
- _notmuch_database_log (notmuch, "Failed to decrypt during indexing. (%d:%d) [%s]\n",
-       err->domain, err->code, err->message);
- g_error_free(err);
+    if (!attempted)
+ return;
+    if (err || !clear) {
+ if (err) {
+    _notmuch_database_log (notmuch, "Failed to decrypt during indexing. (%d:%d) [%s]\n",
+   err->domain, err->code, err->message);
+    g_error_free(err);
+ } else {
+    _notmuch_database_log (notmuch, "Failed to decrypt during indexing. (unknown error)\n");
+ }
  /* Indicate that we failed to decrypt during indexing */
  status = notmuch_message_add_property (message, "index.decryption", "failure");
  if (status)
diff --git a/mime-node.c b/mime-node.c
index 815c1787..6d3d5f69 100644
--- a/mime-node.c
+++ b/mime-node.c
@@ -204,8 +204,8 @@ node_decrypt_and_verify (mime_node_t *node, GMimeObject *part,
     if (parent->envelope_file)
  break;
 
- node->decrypt_attempted = true;
- node->decrypted_child = _notmuch_crypto_decrypt (node->ctx->crypto->decrypt,
+ node->decrypted_child = _notmuch_crypto_decrypt (&node->decrypt_attempted,
+ node->ctx->crypto->decrypt,
  parent ? parent->envelope_file : NULL,
  cryptoctx, encrypteddata, &decrypt_result, &err);
     }
diff --git a/util/crypto.c b/util/crypto.c
index 9789f203..ae6b94be 100644
--- a/util/crypto.c
+++ b/util/crypto.c
@@ -140,7 +140,8 @@ void _notmuch_crypto_cleanup (unused(_notmuch_crypto_t *crypto))
 #endif
 
 GMimeObject *
-_notmuch_crypto_decrypt (notmuch_decryption_policy_t decrypt,
+_notmuch_crypto_decrypt (bool *attempted,
+ notmuch_decryption_policy_t decrypt,
  notmuch_message_t *message,
  g_mime_3_unused(GMimeCryptoContext* crypto_ctx),
  GMimeMultipartEncrypted *part,
@@ -158,6 +159,8 @@ _notmuch_crypto_decrypt (notmuch_decryption_policy_t decrypt,
 
  for (list = notmuch_message_get_properties (message, "session-key", TRUE);
      notmuch_message_properties_valid (list); notmuch_message_properties_move_to_next (list)) {
+    if (attempted)
+ *attempted = true;
 #if (GMIME_MAJOR_VERSION < 3)
     ret = g_mime_multipart_encrypted_decrypt_session (part,
       crypto_ctx,
@@ -182,6 +185,8 @@ _notmuch_crypto_decrypt (notmuch_decryption_policy_t decrypt,
     if (decrypt == NOTMUCH_DECRYPT_AUTO)
  return ret;
 
+    if (attempted)
+ *attempted = true;
 #if (GMIME_MAJOR_VERSION < 3)
     ret = g_mime_multipart_encrypted_decrypt(part, crypto_ctx,
      decrypt_result, err);
diff --git a/util/crypto.h b/util/crypto.h
index dc95b4ca..c384601c 100644
--- a/util/crypto.h
+++ b/util/crypto.h
@@ -16,7 +16,8 @@ typedef struct _notmuch_crypto {
 } _notmuch_crypto_t;
 
 GMimeObject *
-_notmuch_crypto_decrypt (notmuch_decryption_policy_t decrypt,
+_notmuch_crypto_decrypt (bool *attempted,
+ notmuch_decryption_policy_t decrypt,
  notmuch_message_t *message,
  GMimeCryptoContext* crypto_ctx,
  GMimeMultipartEncrypted *part,
--
2.14.2

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[PATCH 13/18] cli/new, insert, reindex: change index.try_decrypt to "auto" by default

In reply to this post by Daniel Kahn Gillmor
The new "auto" decryption policy is not only good for "notmuch show"
and "notmuch reindex".  It's also useful for indexing messages --
there's no good reason to not try to go ahead and index the cleartext
of a message that we have a stashed session key for.

This change updates the defaults and tunes the test suite to make sure
that they have taken effect.
---
 doc/man1/notmuch-config.rst   | 2 +-
 lib/indexopts.c               | 8 +++++---
 test/T357-index-decryption.sh | 4 ++--
 3 files changed, 8 insertions(+), 6 deletions(-)

diff --git a/doc/man1/notmuch-config.rst b/doc/man1/notmuch-config.rst
index 14642062..ae7586f3 100644
--- a/doc/man1/notmuch-config.rst
+++ b/doc/man1/notmuch-config.rst
@@ -154,7 +154,7 @@ The available configuration items are described below.
         DO NOT USE ``index.try_decrypt=true`` without considering the
         security of your index.
 
-        Default: ``false``.
+        Default: ``auto``.
 
     **built_with.<name>**
 
diff --git a/lib/indexopts.c b/lib/indexopts.c
index 93a2c9eb..a61d6420 100644
--- a/lib/indexopts.c
+++ b/lib/indexopts.c
@@ -26,7 +26,7 @@ notmuch_database_get_default_indexopts (notmuch_database_t *db)
     notmuch_indexopts_t *ret = talloc_zero (db, notmuch_indexopts_t);
     if (!ret)
  return ret;
-    ret->crypto.decrypt = NOTMUCH_DECRYPT_FALSE;
+    ret->crypto.decrypt = NOTMUCH_DECRYPT_AUTO;
 
     char * try_decrypt;
     notmuch_status_t err = notmuch_database_get_config (db, "index.try_decrypt", &try_decrypt);
@@ -38,8 +38,10 @@ notmuch_database_get_default_indexopts (notmuch_database_t *db)
     (!(strcasecmp(try_decrypt, "yes"))) ||
     (!(strcasecmp(try_decrypt, "1"))))
     notmuch_indexopts_set_try_decrypt (ret, NOTMUCH_DECRYPT_TRUE);
- else if (!strcasecmp(try_decrypt, "auto"))
-    notmuch_indexopts_set_try_decrypt (ret, NOTMUCH_DECRYPT_AUTO);
+ else if ((!(strcasecmp(try_decrypt, "false"))) ||
+ (!(strcasecmp(try_decrypt, "no"))) ||
+ (!(strcasecmp(try_decrypt, "0"))))
+    notmuch_indexopts_set_try_decrypt (ret, NOTMUCH_DECRYPT_FALSE);
     }
 
     free (try_decrypt);
diff --git a/test/T357-index-decryption.sh b/test/T357-index-decryption.sh
index 30bdf704..7fc59f1e 100755
--- a/test/T357-index-decryption.sh
+++ b/test/T357-index-decryption.sh
@@ -142,7 +142,7 @@ test_expect_equal \
 
 # ensure no session keys are present:
 test_begin_subtest 'reindex using only session keys'
-test_expect_success 'notmuch reindex --try-decrypt=auto tag:encrypted and property:index.decryption=success'
+test_expect_success 'notmuch reindex tag:encrypted and property:index.decryption=success'
 test_begin_subtest "reindexed encrypted messages, decrypting only with session keys"
 output=$(notmuch search wumpus)
 expected=''
@@ -190,7 +190,7 @@ notmuch restore <<EOF
 #notmuch-dump batch-tag:3 config,properties,tags
 #= [hidden email] session-key=9%3AFC09987F5F927CC0CC0EE80A96E4C5BBF4A499818FB591207705DFDDD6112CF9
 EOF
-notmuch reindex --try-decrypt=auto id:[hidden email]
+notmuch reindex id:[hidden email]
 output=$(notmuch search sekrit)
 expected='thread:0000000000000001   2016-12-22 [1/1] Daniel Kahn Gillmor; encrypted message (encrypted inbox unread)'
 test_expect_equal \
--
2.14.2

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[PATCH 14/18] cli/reindex: destroy stashed session keys when --try-decrypt=false

In reply to this post by Daniel Kahn Gillmor
There are some situations where the user wants to get rid of the
cleartext index of a message.  For example, if they're indexing
encrypted messages normally, but suddenly they run across a message
that they really don't want any trace of in their index.

In that case, the natural thing to do is:

   notmuch reindex --try-decrypt=false id:[hidden email]

But of course, clearing the cleartext index without clearing the
stashed session key is just silly.  So we do the expected thing and
also destroy any stashed session keys while we're destroying the index
of the cleartext.

Note that stashed session keys are stored in the xapian database, but
xapian does not currently allow safe deletion (see
https://trac.xapian.org/ticket/742).

As a workaround, after removing session keys and cleartext material
from the database, the user probably should do something like "notmuch
compact" to try to purge whatever recoverable data is left in the
xapian freelist.  This problem really needs to be addressed within
xapian, though, if we want it fixed right.
---
 doc/man1/notmuch-reindex.rst  |  3 +++
 lib/message.cc                |  5 +++++
 test/T357-index-decryption.sh | 17 +++++++++++++++++
 3 files changed, 25 insertions(+)

diff --git a/doc/man1/notmuch-reindex.rst b/doc/man1/notmuch-reindex.rst
index b15981a2..6f5e48a9 100644
--- a/doc/man1/notmuch-reindex.rst
+++ b/doc/man1/notmuch-reindex.rst
@@ -30,6 +30,9 @@ Supported options for **reindex** include
         the user's secret keys.  If decryption is successful, index
         the cleartext itself.
 
+        If ``false``, notmuch reindex will also delete any stashed
+        session keys for all messages matching the search terms.
+
         Be aware that the index is likely sufficient to reconstruct
         the cleartext of the message itself, so please ensure that the
         notmuch message index is adequately protected. DO NOT USE
diff --git a/lib/message.cc b/lib/message.cc
index 12743460..cfd99130 100644
--- a/lib/message.cc
+++ b/lib/message.cc
@@ -2002,6 +2002,11 @@ notmuch_message_reindex (notmuch_message_t *message,
     ret = notmuch_message_remove_all_properties_with_prefix (message, "index.");
     if (ret)
  goto DONE; /* XXX TODO: distinguish from other error returns above? */
+    if (indexopts && notmuch_indexopts_get_try_decrypt (indexopts) == NOTMUCH_DECRYPT_FALSE) {
+ ret = notmuch_message_remove_all_properties (message, "session-key");
+ if (ret)
+    goto DONE;
+    }
 
     /* re-add the filenames with the associated indexopts */
     for (; notmuch_filenames_valid (orig_filenames);
diff --git a/test/T357-index-decryption.sh b/test/T357-index-decryption.sh
index 7fc59f1e..4f5a501a 100755
--- a/test/T357-index-decryption.sh
+++ b/test/T357-index-decryption.sh
@@ -218,6 +218,23 @@ test_expect_equal \
     "$output" \
     "$expected"
 
+test_begin_subtest "purging stashed session keys should lose access to the cleartext"
+notmuch reindex --try-decrypt=false id:[hidden email]
+output=$(notmuch search sekrit)
+expected=''
+test_expect_equal \
+    "$output" \
+    "$expected"
+
+test_begin_subtest "and cleartext should be unrecoverable now that there are no stashed session keys"
+notmuch dump
+notmuch reindex --try-decrypt=true id:[hidden email]
+output=$(notmuch search sekrit)
+expected=''
+test_expect_equal \
+    "$output" \
+    "$expected"
+
 
 # TODO: test removal of a message from the message store between
 # indexing and reindexing.
--
2.14.2

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[PATCH 15/18] crypto: actually stash session keys when try-decrypt=true

In reply to this post by Daniel Kahn Gillmor
If you're going to store the cleartext index of an encrypted message,
in most situations you might just as well store the session key.
Doing this storage has efficiency and recoverability advantages.

Combined with a schedule of regular OpenPGP subkey rotation and
destruction, this can also offer security benefits, like "deletable
e-mail", which is the store-and-forward analog to "forward secrecy".

But wait, i hear you saying, i have a special need to store cleartext
indexes but it's really bad for me to store session keys!  Maybe
(let's imagine) i get lots of e-mails with incriminating photos
attached, and i want to be able to search for them by the text in the
e-mail, but i don't want someone with access to the index to be
actually able to see the photos themselves.

Fret not, the next patch in this series will support your wacky
uncommon use case.
---
 doc/man1/notmuch-config.rst     | 10 ++++++----
 doc/man1/notmuch-insert.rst     | 13 +++++++------
 doc/man1/notmuch-new.rst        | 21 +++++++++++----------
 doc/man1/notmuch-reindex.rst    | 10 +++++-----
 doc/man7/notmuch-properties.rst |  4 ++++
 lib/index.cc                    | 16 +++++++++++++++-
 test/T357-index-decryption.sh   | 18 +++++++++++++++++-
 util/crypto.c                   | 16 +++++++++++++++-
 8 files changed, 80 insertions(+), 28 deletions(-)

diff --git a/doc/man1/notmuch-config.rst b/doc/man1/notmuch-config.rst
index ae7586f3..5adde070 100644
--- a/doc/man1/notmuch-config.rst
+++ b/doc/man1/notmuch-config.rst
@@ -143,10 +143,12 @@ The available configuration items are described below.
         **[STORED IN DATABASE]**
         When indexing an encrypted e-mail message, if this variable is
         set to ``true``, notmuch will try to decrypt the message and
-        index the cleartext.  If ``auto``, it will try to index the
-        cleartext if a stashed session key is already known for the message,
-        but will not try to access your secret keys.  Use ``false`` to
-        avoid decrypting even when a session key is already known.
+        index the cleartext, stashing a copy of any discovered session
+        keys for the message.  If ``auto``, it will try to index the
+        cleartext if a stashed session key is already known for the message
+        (e.g. from a previous copy), but will not try to access your
+        secret keys.  Use ``false`` to avoid decrypting even when a
+        stashed session key is already present.
 
         Be aware that the notmuch index is likely sufficient to
         reconstruct the cleartext of the message itself, so please
diff --git a/doc/man1/notmuch-insert.rst b/doc/man1/notmuch-insert.rst
index a5505b5b..3e6f538d 100644
--- a/doc/man1/notmuch-insert.rst
+++ b/doc/man1/notmuch-insert.rst
@@ -53,12 +53,13 @@ Supported options for **insert** include
     ``--try-decrypt=(true|auto|false)``
 
         If ``true`` and the message is encrypted, try to decrypt the
-        message while indexing.  If ``auto``, and notmuch already
-        knows about a session key for the message, it will try
-        decrypting using that session key but will not try to access
-        the user's secret keys.  If decryption is successful, index
-        the cleartext itself.  Either way, the message is always
-        stored to disk in its original form (ciphertext).
+        message while indexing, storing any session keys discovered.
+        If ``auto``, and notmuch already knows about a session key for
+        the message, it will try decrypting using that session key but
+        will not try to access the user's secret keys.  If decryption
+        is successful, index the cleartext itself.  Either way, the
+        message is always stored to disk in its original form
+        (ciphertext).
 
         Be aware that the index is likely sufficient to reconstruct
         the cleartext of the message itself, so please ensure that the
diff --git a/doc/man1/notmuch-new.rst b/doc/man1/notmuch-new.rst
index d8cb77f5..351b7591 100644
--- a/doc/man1/notmuch-new.rst
+++ b/doc/man1/notmuch-new.rst
@@ -46,16 +46,17 @@ Supported options for **new** include
     ``--try-decrypt=(true|auto|false)``
 
         If ``true``, when encountering an encrypted message, try to
-        decrypt it while indexing.  If decryption is successful, index
-        the cleartext itself.  If ``auto``, try to use any session key
-        already known to belong to this message, but do not attempt to
-        use the user's secret keys.
-
-        Be aware that the index is likely
-        sufficient to reconstruct the cleartext of the message itself,
-        so please ensure that the notmuch message index is adequately
-        protected.  DO NOT USE ``--try-decrypt=true`` without
-        considering the security of your index.
+        decrypt it while indexing, and store any discovered session
+        keys.  If ``auto``, try to use any session key already known
+        to belong to this message, but do not attempt to use the
+        user's secret keys.  If decryption is successful, index the
+        cleartext of the message.
+
+        Be aware that the index is likely sufficient to reconstruct
+        the cleartext of the message itself, so please ensure that the
+        notmuch message index is adequately protected.  DO NOT USE
+        ``--try-decrypt=true`` without considering the security of
+        your index.
 
         See also ``index.try_decrypt`` in **notmuch-config(1)**.
 
diff --git a/doc/man1/notmuch-reindex.rst b/doc/man1/notmuch-reindex.rst
index 6f5e48a9..3b99b934 100644
--- a/doc/man1/notmuch-reindex.rst
+++ b/doc/man1/notmuch-reindex.rst
@@ -24,11 +24,11 @@ Supported options for **reindex** include
     ``--try-decrypt=(true|auto|false)``
 
         If ``true``, when encountering an encrypted message, try to
-        decrypt it while reindexing.  If ``auto``, and notmuch already
-        knows about a session key for the message, it will try
-        decrypting using that session key but will not try to access
-        the user's secret keys.  If decryption is successful, index
-        the cleartext itself.
+        decrypt it while reindexing, storing any session keys
+        discovered.  If ``auto``, and notmuch already knows about a
+        session key for the message, it will try decrypting using that
+        session key but will not try to access the user's secret keys.
+        If decryption is successful, index the cleartext itself.
 
         If ``false``, notmuch reindex will also delete any stashed
         session keys for all messages matching the search terms.
diff --git a/doc/man7/notmuch-properties.rst b/doc/man7/notmuch-properties.rst
index e2ab43be..5dcbb4ae 100644
--- a/doc/man7/notmuch-properties.rst
+++ b/doc/man7/notmuch-properties.rst
@@ -98,6 +98,10 @@ of its normal activity.
     message.  This includes attachments, cryptographic signatures, and
     other material that cannot be reconstructed from the index alone.
 
+    See ``index.try_decrypt`` in **notmuch-config(1)** for more
+    details about how to set notmuch's policy on when to store session
+    keys.
+
     The session key should be in the ASCII text form produced by
     GnuPG.  For OpenPGP, that consists of a decimal representation of
     the hash algorithm used (identified by number from RFC 4880,
diff --git a/lib/index.cc b/lib/index.cc
index e2701755..06470919 100644
--- a/lib/index.cc
+++ b/lib/index.cc
@@ -549,11 +549,15 @@ _index_encrypted_mime_part (notmuch_message_t *message,
     }
 #endif
     bool attempted = false;
+    GMimeDecryptResult *decrypt_result = NULL;
+    bool get_sk = (notmuch_indexopts_get_try_decrypt (indexopts) == NOTMUCH_DECRYPT_TRUE);
     clear = _notmuch_crypto_decrypt (&attempted, notmuch_indexopts_get_try_decrypt (indexopts),
-     message, crypto_ctx, encrypted_data, NULL, &err);
+     message, crypto_ctx, encrypted_data, get_sk ? &decrypt_result : NULL, &err);
     if (!attempted)
  return;
     if (err || !clear) {
+ if (decrypt_result)
+    g_object_unref (decrypt_result);
  if (err) {
     _notmuch_database_log (notmuch, "Failed to decrypt during indexing. (%d:%d) [%s]\n",
    err->domain, err->code, err->message);
@@ -568,6 +572,16 @@ _index_encrypted_mime_part (notmuch_message_t *message,
   "property (%d)\n", status);
  return;
     }
+    if (decrypt_result) {
+ if (get_sk) {
+    status = notmuch_message_add_property (message, "session-key",
+   g_mime_decrypt_result_get_session_key (decrypt_result));
+    if (status)
+ _notmuch_database_log (notmuch, "failed to add session-key "
+       "property (%d)\n", status);
+ }
+ g_object_unref (decrypt_result);
+    }
     _index_mime_part (message, indexopts, clear);
     g_object_unref (clear);
 
diff --git a/test/T357-index-decryption.sh b/test/T357-index-decryption.sh
index 4f5a501a..3ac8c43e 100755
--- a/test/T357-index-decryption.sh
+++ b/test/T357-index-decryption.sh
@@ -48,6 +48,14 @@ test_expect_equal \
     "$output" \
     "$expected"
 
+test_begin_subtest "show the message body of the encrypted message"
+notmuch dump wumpus
+output=$(notmuch show wumpus | awk '/^\014part}/{ f=0 }; { if (f) { print $0 } } /^\014part{ ID: 3/{ f=1 }')
+expected='This is a test encrypted message with a wumpus.'
+test_expect_equal \
+    "$output" \
+    "$expected"
+
 
 test_begin_subtest "message should go away after deletion"
 # cache the message in an env var and remove it:
@@ -129,10 +137,18 @@ test_expect_equal \
     "$output" \
     "$expected"
 
+# try a simple reindexx
+test_begin_subtest 'reindex in auto mode'
+test_expect_success 'notmuch reindex tag:encrypted and property:index.decryption=success'
+test_begin_subtest "reindexed encrypted messages, should not have changed"
+output=$(notmuch search wumpus)
+test_expect_equal \
+    "$output" \
+    "$expected"
 
 # try to remove cleartext indexing
 test_begin_subtest 'reindex without cleartext'
-test_expect_success 'notmuch reindex tag:encrypted and property:index.decryption=success'
+test_expect_success 'notmuch reindex --try-decrypt=false tag:encrypted and property:index.decryption=success'
 test_begin_subtest "reindexed encrypted messages, without cleartext"
 output=$(notmuch search wumpus)
 expected=''
diff --git a/util/crypto.c b/util/crypto.c
index ae6b94be..ba9bfa7b 100644
--- a/util/crypto.c
+++ b/util/crypto.c
@@ -188,10 +188,24 @@ _notmuch_crypto_decrypt (bool *attempted,
     if (attempted)
  *attempted = true;
 #if (GMIME_MAJOR_VERSION < 3)
+#if (GMIME_MAJOR_VERSION == 2 && GMIME_MINOR_VERSION == 6 && GMIME_MICRO_VERSION >= 21)
+    gboolean oldgetsk = g_mime_crypto_context_get_retrieve_session_key (crypto_ctx);
+    gboolean newgetsk = (decrypt_result);
+    if (newgetsk != oldgetsk)
+ /* This could return an error, but we can't do anything about it, so ignore it */
+ g_mime_crypto_context_set_retrieve_session_key (crypto_ctx, newgetsk, NULL);
+#endif
     ret = g_mime_multipart_encrypted_decrypt(part, crypto_ctx,
      decrypt_result, err);
+#if (GMIME_MAJOR_VERSION == 2 && GMIME_MINOR_VERSION == 6 && GMIME_MICRO_VERSION >= 21)
+    if (newgetsk != oldgetsk)
+ g_mime_crypto_context_set_retrieve_session_key (crypto_ctx, oldgetsk, NULL);
+#endif
 #else
-    ret = g_mime_multipart_encrypted_decrypt(part, GMIME_DECRYPT_NONE, NULL,
+    GMimeDecryptFlags flags = GMIME_DECRYPT_NONE;
+    if (decrypt_result)
+ flags |= GMIME_DECRYPT_EXPORT_SESSION_KEY;
+    ret = g_mime_multipart_encrypted_decrypt(part, flags, NULL,
      decrypt_result, err);
 #endif
     return ret;
--
2.14.2

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[PATCH 16/18] crypto: add --try-decrypt=nostash to avoid stashing session keys

In reply to this post by Daniel Kahn Gillmor
Here's the configuration choice for people who want a cleartext index,
but don't want stashed session keys.

Interestingly, this "nostash" decryption policy is actually the same
policy that should be used by "notmuch show" and "notmuch reply",
since they never modify the index or database when they are invoked
with --decrypt.

We take advantage of this parallel to tune the behavior of those
programs so that we're not requesting session keys from GnuPG during
"show" and "reply" that we would then otherwise just throw away.
---
 completion/notmuch-completion.bash |  6 +++---
 doc/man1/notmuch-config.rst        | 10 ++++++++--
 doc/man1/notmuch-insert.rst        | 11 +++++++----
 doc/man1/notmuch-new.rst           | 11 +++++++----
 doc/man1/notmuch-reindex.rst       | 11 +++++++----
 lib/indexopts.c                    |  2 ++
 lib/notmuch.h                      |  1 +
 notmuch-reply.c                    |  2 +-
 notmuch-show.c                     |  3 ++-
 notmuch.c                          |  1 +
 test/T357-index-decryption.sh      | 26 ++++++++++++++++++++++++++
 util/crypto.c                      |  4 ++--
 12 files changed, 67 insertions(+), 21 deletions(-)

diff --git a/completion/notmuch-completion.bash b/completion/notmuch-completion.bash
index 53d7380b..29256210 100644
--- a/completion/notmuch-completion.bash
+++ b/completion/notmuch-completion.bash
@@ -288,7 +288,7 @@ _notmuch_insert()
     return
     ;;
  --try-decrypt)
-    COMPREPLY=( $( compgen -W "true false auto" -- "${cur}" ) )
+    COMPREPLY=( $( compgen -W "true false auto nostash" -- "${cur}" ) )
     return
     ;;
     esac
@@ -320,7 +320,7 @@ _notmuch_new()
     $split &&
     case "${prev}" in
  --try-decrypt)
-    COMPREPLY=( $( compgen -W "true false auto" -- "${cur}" ) )
+    COMPREPLY=( $( compgen -W "true false auto nostash" -- "${cur}" ) )
     return
     ;;
     esac
@@ -442,7 +442,7 @@ _notmuch_reindex()
     $split &&
     case "${prev}" in
  --try-decrypt)
-    COMPREPLY=( $( compgen -W "true false auto" -- "${cur}" ) )
+    COMPREPLY=( $( compgen -W "true false auto nostash" -- "${cur}" ) )
     return
     ;;
     esac
diff --git a/doc/man1/notmuch-config.rst b/doc/man1/notmuch-config.rst
index 5adde070..d9e22653 100644
--- a/doc/man1/notmuch-config.rst
+++ b/doc/man1/notmuch-config.rst
@@ -141,6 +141,9 @@ The available configuration items are described below.
     **index.try_decrypt**
 
         **[STORED IN DATABASE]**
+
+        One of ``false``, ``auto``, ``nostash``, or ``true``.
+
         When indexing an encrypted e-mail message, if this variable is
         set to ``true``, notmuch will try to decrypt the message and
         index the cleartext, stashing a copy of any discovered session
@@ -150,11 +153,14 @@ The available configuration items are described below.
         secret keys.  Use ``false`` to avoid decrypting even when a
         stashed session key is already present.
 
+        ``nostash`` is the same as ``true`` except that it will not
+        stash newly-discovered session keys in the database.
+
         Be aware that the notmuch index is likely sufficient to
         reconstruct the cleartext of the message itself, so please
         ensure that the notmuch message index is adequately protected.
-        DO NOT USE ``index.try_decrypt=true`` without considering the
-        security of your index.
+        DO NOT USE ``index.try_decrypt=true`` or ``index-only``
+        without considering the security of your index.
 
         Default: ``auto``.
 
diff --git a/doc/man1/notmuch-insert.rst b/doc/man1/notmuch-insert.rst
index 3e6f538d..bf659a3d 100644
--- a/doc/man1/notmuch-insert.rst
+++ b/doc/man1/notmuch-insert.rst
@@ -50,10 +50,10 @@ Supported options for **insert** include
     ``--no-hooks``
         Prevent hooks from being run.
 
-    ``--try-decrypt=(true|auto|false)``
+    ``--try-decrypt=(true|nostash|auto|false)``
 
         If ``true`` and the message is encrypted, try to decrypt the
-        message while indexing, storing any session keys discovered.
+        message while indexing, stashing any session keys discovered.
         If ``auto``, and notmuch already knows about a session key for
         the message, it will try decrypting using that session key but
         will not try to access the user's secret keys.  If decryption
@@ -61,11 +61,14 @@ Supported options for **insert** include
         message is always stored to disk in its original form
         (ciphertext).
 
+        ``nostash`` is the same as ``true`` except that it will not
+        stash newly-discovered session keys in the database.
+
         Be aware that the index is likely sufficient to reconstruct
         the cleartext of the message itself, so please ensure that the
         notmuch message index is adequately protected. DO NOT USE
-        ``--try-decrypt=true`` without considering the security of
-        your index.
+        ``--try-decrypt=true`` or ``nostash`` without considering
+        the security of your index.
 
         See also ``index.try_decrypt`` in **notmuch-config(1)**.
 
diff --git a/doc/man1/notmuch-new.rst b/doc/man1/notmuch-new.rst
index 351b7591..2660988d 100644
--- a/doc/man1/notmuch-new.rst
+++ b/doc/man1/notmuch-new.rst
@@ -43,20 +43,23 @@ Supported options for **new** include
     ``--quiet``
         Do not print progress or results.
 
-    ``--try-decrypt=(true|auto|false)``
+    ``--try-decrypt=(true|nostash|auto|false)``
 
         If ``true``, when encountering an encrypted message, try to
-        decrypt it while indexing, and store any discovered session
+        decrypt it while indexing, and stash any discovered session
         keys.  If ``auto``, try to use any session key already known
         to belong to this message, but do not attempt to use the
         user's secret keys.  If decryption is successful, index the
         cleartext of the message.
 
+        ``nostash`` is the same as ``true`` except that it will not
+        stash newly-discovered session keys in the database.
+
         Be aware that the index is likely sufficient to reconstruct
         the cleartext of the message itself, so please ensure that the
         notmuch message index is adequately protected.  DO NOT USE
-        ``--try-decrypt=true`` without considering the security of
-        your index.
+        ``--try-decrypt=true`` or ``nostash`` without considering
+        the security of your index.
 
         See also ``index.try_decrypt`` in **notmuch-config(1)**.
 
diff --git a/doc/man1/notmuch-reindex.rst b/doc/man1/notmuch-reindex.rst
index 3b99b934..7883e0cb 100644
--- a/doc/man1/notmuch-reindex.rst
+++ b/doc/man1/notmuch-reindex.rst
@@ -21,23 +21,26 @@ messages using the supplied options.
 
 Supported options for **reindex** include
 
-    ``--try-decrypt=(true|auto|false)``
+    ``--try-decrypt=(true|nostash|auto|false)``
 
         If ``true``, when encountering an encrypted message, try to
-        decrypt it while reindexing, storing any session keys
+        decrypt it while reindexing, stashing any session keys
         discovered.  If ``auto``, and notmuch already knows about a
         session key for the message, it will try decrypting using that
         session key but will not try to access the user's secret keys.
         If decryption is successful, index the cleartext itself.
 
+        ``nostash`` is the same as ``true`` except that it will not
+        stash newly-discovered session keys in the database.
+
         If ``false``, notmuch reindex will also delete any stashed
         session keys for all messages matching the search terms.
 
         Be aware that the index is likely sufficient to reconstruct
         the cleartext of the message itself, so please ensure that the
         notmuch message index is adequately protected. DO NOT USE
-        ``--try-decrypt=true`` without considering the security of
-        your index.
+        ``--try-decrypt=true`` or ``nostash`` without considering
+        the security of your index.
 
         See also ``index.try_decrypt`` in **notmuch-config(1)**.
 
diff --git a/lib/indexopts.c b/lib/indexopts.c
index a61d6420..e698dcea 100644
--- a/lib/indexopts.c
+++ b/lib/indexopts.c
@@ -42,6 +42,8 @@ notmuch_database_get_default_indexopts (notmuch_database_t *db)
  (!(strcasecmp(try_decrypt, "no"))) ||
  (!(strcasecmp(try_decrypt, "0"))))
     notmuch_indexopts_set_try_decrypt (ret, NOTMUCH_DECRYPT_FALSE);
+ else if (!strcasecmp(try_decrypt, "nostash"))
+    notmuch_indexopts_set_try_decrypt (ret, NOTMUCH_DECRYPT_NOSTASH);
     }
 
     free (try_decrypt);
diff --git a/lib/notmuch.h b/lib/notmuch.h
index 7b1c61ad..103a7091 100644
--- a/lib/notmuch.h
+++ b/lib/notmuch.h
@@ -2242,6 +2242,7 @@ typedef enum {
     NOTMUCH_DECRYPT_FALSE,
     NOTMUCH_DECRYPT_TRUE,
     NOTMUCH_DECRYPT_AUTO,
+    NOTMUCH_DECRYPT_NOSTASH,
 } notmuch_decryption_policy_t;
 
 /**
diff --git a/notmuch-reply.c b/notmuch-reply.c
index fd990a9a..5cdf642b 100644
--- a/notmuch-reply.c
+++ b/notmuch-reply.c
@@ -730,7 +730,7 @@ notmuch_reply_command (notmuch_config_t *config, int argc, char *argv[])
 
     notmuch_process_shared_options (argv[0]);
     if (decrypt_set)
- params.crypto.decrypt = decrypt ? NOTMUCH_DECRYPT_TRUE : NOTMUCH_DECRYPT_FALSE;
+ params.crypto.decrypt = decrypt ? NOTMUCH_DECRYPT_NOSTASH : NOTMUCH_DECRYPT_FALSE;
 
     notmuch_exit_if_unsupported_format ();
 
diff --git a/notmuch-show.c b/notmuch-show.c
index c8f5a48f..4e22424b 100644
--- a/notmuch-show.c
+++ b/notmuch-show.c
@@ -1121,7 +1121,8 @@ notmuch_show_command (notmuch_config_t *config, int argc, char *argv[])
 
     if (decrypt_set) {
  if (decrypt) {
-    params.crypto.decrypt = NOTMUCH_DECRYPT_TRUE;
+    /* we do not need or want to ask for session keys */
+    params.crypto.decrypt = NOTMUCH_DECRYPT_NOSTASH;
     /* decryption implies verification */
     params.crypto.verify = true;
  } else {
diff --git a/notmuch.c b/notmuch.c
index 62706748..2f43ad28 100644
--- a/notmuch.c
+++ b/notmuch.c
@@ -104,6 +104,7 @@ const notmuch_opt_desc_t  notmuch_shared_indexing_options [] = {
       (notmuch_keyword_t []){ { "false", NOTMUCH_DECRYPT_FALSE },
       { "true", NOTMUCH_DECRYPT_TRUE },
       { "auto", NOTMUCH_DECRYPT_AUTO },
+      { "nostash", NOTMUCH_DECRYPT_NOSTASH },
       { 0, 0 } },
       .name = "try-decrypt" },
     { }
diff --git a/test/T357-index-decryption.sh b/test/T357-index-decryption.sh
index 3ac8c43e..8aef4354 100755
--- a/test/T357-index-decryption.sh
+++ b/test/T357-index-decryption.sh
@@ -182,6 +182,32 @@ test_expect_equal \
     "$output" \
     "$expected"
 
+test_begin_subtest "index cleartext without keeping session keys"
+test_expect_success "notmuch reindex --try-decrypt=nostash tag:blarney"
+
+test_begin_subtest "Ensure that the indexed terms are present"
+output=$(notmuch search wumpus)
+test_expect_equal \
+    "$output" \
+    "$expected"
+
+test_begin_subtest "show one of the messages with --decrypt"
+output=$(notmuch show --decrypt thread:0000000000000001 | awk '/^\014part}/{ f=0 }; { if (f) { print $0 } } /^\014part{ ID: 3/{ f=1 }')
+expected='This is a test encrypted message with a wumpus.'
+test_expect_equal \
+    "$output" \
+    "$expected"
+
+test_begin_subtest "Ensure that we cannot show the message without --decrypt"
+output=$(notmuch show thread:0000000000000001 | awk '/^\014part}/{ f=0 }; { if (f) { print $0 } } /^\014part{ ID: 3/{ f=1 }')
+expected='Non-text part: application/octet-stream'
+test_expect_equal \
+    "$output" \
+    "$expected"
+
+
+
+
 add_email_corpus crypto
 
 test_begin_subtest "indexing message fails when secret key not available"
diff --git a/util/crypto.c b/util/crypto.c
index ba9bfa7b..ac018005 100644
--- a/util/crypto.c
+++ b/util/crypto.c
@@ -190,7 +190,7 @@ _notmuch_crypto_decrypt (bool *attempted,
 #if (GMIME_MAJOR_VERSION < 3)
 #if (GMIME_MAJOR_VERSION == 2 && GMIME_MINOR_VERSION == 6 && GMIME_MICRO_VERSION >= 21)
     gboolean oldgetsk = g_mime_crypto_context_get_retrieve_session_key (crypto_ctx);
-    gboolean newgetsk = (decrypt_result);
+    gboolean newgetsk = (decrypt == NOTMUCH_DECRYPT_TRUE && decrypt_result);
     if (newgetsk != oldgetsk)
  /* This could return an error, but we can't do anything about it, so ignore it */
  g_mime_crypto_context_set_retrieve_session_key (crypto_ctx, newgetsk, NULL);
@@ -203,7 +203,7 @@ _notmuch_crypto_decrypt (bool *attempted,
 #endif
 #else
     GMimeDecryptFlags flags = GMIME_DECRYPT_NONE;
-    if (decrypt_result)
+    if (decrypt == NOTMUCH_DECRYPT_TRUE && decrypt_result)
  flags |= GMIME_DECRYPT_EXPORT_SESSION_KEY;
     ret = g_mime_multipart_encrypted_decrypt(part, flags, NULL,
      decrypt_result, err);
--
2.14.2

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[PATCH 17/18] docs: clean up documentation about decryption policies

In reply to this post by Daniel Kahn Gillmor
Now that the range of sensible decryption policies has come into full
view, we take a bit of space to document the distinctions.

Most people will use either "auto" or "true" -- but we provide "false"
and "nostash" to handle use cases that might reasonably be requested.

Note also that these can be combined in sensible ways.  Like, if your
mail comes in regularly to a service that doesn't have access to your
secret keys, but does have access to your index, and you feel
comfortable adding selected encrypted messages to the index after
you've read them, you could stay in "auto" normally, and then when you
find yourself reading an indexable message (e.g. one you want to be
able to search for in the future, and that you don't mind exposing to
whatever entities have access to your inde), you can do:

    notmuch reindex --try-decrypt=true id:[hidden email]

That leaves your default the same (still "auto") but you get the
cleartext index and stashed session key benefits for that particular
message.
---
 doc/man1/notmuch-config.rst | 44 ++++++++++++++++++++++++++++++++++++++------
 1 file changed, 38 insertions(+), 6 deletions(-)

diff --git a/doc/man1/notmuch-config.rst b/doc/man1/notmuch-config.rst
index d9e22653..6b7d5db2 100644
--- a/doc/man1/notmuch-config.rst
+++ b/doc/man1/notmuch-config.rst
@@ -142,7 +142,9 @@ The available configuration items are described below.
 
         **[STORED IN DATABASE]**
 
-        One of ``false``, ``auto``, ``nostash``, or ``true``.
+        Policy for decrypting encrypted messages during indexing.
+        Must be one of: ``false``, ``auto``, ``nostash``, or
+        ``true``.
 
         When indexing an encrypted e-mail message, if this variable is
         set to ``true``, notmuch will try to decrypt the message and
@@ -156,11 +158,40 @@ The available configuration items are described below.
         ``nostash`` is the same as ``true`` except that it will not
         stash newly-discovered session keys in the database.
 
-        Be aware that the notmuch index is likely sufficient to
-        reconstruct the cleartext of the message itself, so please
-        ensure that the notmuch message index is adequately protected.
-        DO NOT USE ``index.try_decrypt=true`` or ``index-only``
-        without considering the security of your index.
+        From the command line (i.e. during **notmuch-new(1)**,
+        **notmuch-insert(1)**, or **notmuch-reindex**), the user can
+        override the database's stored decryption policy with the
+        ``--try-decrypt=`` option.
+
+        Here is a table that summarizes the functionality of each of
+        these policies:
+
+        +------------------------+-------+------+---------+------+
+        |                        | false | auto | nostash | true |
+        +========================+=======+======+=========+======+
+        | Index cleartext using  |       |  X   |    X    |  X   |
+        | stashed session keys   |       |      |         |      |
+        +------------------------+-------+------+---------+------+
+        | Index cleartext        |       |      |    X    |  X   |
+        | using secret keys      |       |      |         |      |
+        +------------------------+-------+------+---------+------+
+        | Stash session keys     |       |      |         |  X   |
+        +------------------------+-------+------+---------+------+
+        | Delete stashed session |   X   |      |         |      |
+        | keys on reindex        |       |      |         |      |
+        +------------------------+-------+------+---------+------+
+
+        Stashed session keys are kept in the database as properties
+        associated with the message.  See ``session-key`` in
+        **notmuch-properties(7)** for more details about how they can
+        be useful.
+
+        Be aware that the notmuch index itself (whether session keys
+        are stashed or not) is likely sufficient to reconstruct a
+        close approximation of the cleartext of the message itself, so
+        please ensure that the notmuch message index is adequately
+        protected.  DO NOT SET ``index.try_decrypt`` to ``true`` or
+        ``index-only`` without considering the security of your index.
 
         Default: ``auto``.
 
@@ -200,5 +231,6 @@ SEE ALSO
 **notmuch-restore(1)**,
 **notmuch-search(1)**,
 **notmuch-search-terms(7)**,
+**notmuch-properties(7)**,
 **notmuch-show(1)**,
 **notmuch-tag(1)**
--
2.14.2

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[PATCH 18/18] python: add try_decrypt argument to Database.index_file()

In reply to this post by Daniel Kahn Gillmor
We adopt a pythonic idiom here with an optional argument, rather than
exposing the user to the C indexopts object directly.
---
 bindings/python/notmuch/database.py | 46 +++++++++++++++++++++++++++++++++++--
 bindings/python/notmuch/globals.py  |  5 ++++
 2 files changed, 49 insertions(+), 2 deletions(-)

diff --git a/bindings/python/notmuch/database.py b/bindings/python/notmuch/database.py
index 1279804a..bbce5cc2 100644
--- a/bindings/python/notmuch/database.py
+++ b/bindings/python/notmuch/database.py
@@ -28,6 +28,7 @@ from .globals import (
     _str,
     NotmuchDatabaseP,
     NotmuchDirectoryP,
+    NotmuchIndexoptsP,
     NotmuchMessageP,
     NotmuchTagsP,
 )
@@ -72,6 +73,9 @@ class Database(object):
     MODE = Enum(['READ_ONLY', 'READ_WRITE'])
     """Constants: Mode in which to open the database"""
 
+    DECRYPTION_POLICY = Enum(['FALSE', 'TRUE', 'AUTO', 'NOSTASH'])
+    """Constants: policies for decrypting messages during indexing"""
+
     """notmuch_database_get_directory"""
     _get_directory = nmlib.notmuch_database_get_directory
     _get_directory.argtypes = [NotmuchDatabaseP, c_char_p, POINTER(NotmuchDirectoryP)]
@@ -400,13 +404,25 @@ class Database(object):
         # return the Directory, init it with the absolute path
         return Directory(abs_dirpath, dir_p, self)
 
+    _get_default_indexopts = nmlib.notmuch_database_get_default_indexopts
+    _get_default_indexopts.argtypes = [NotmuchDatabaseP]
+    _get_default_indexopts.restype = NotmuchIndexoptsP
+
+    _indexopts_set_try_decrypt = nmlib.notmuch_indexopts_set_try_decrypt
+    _indexopts_set_try_decrypt.argtypes = [NotmuchIndexoptsP, c_uint]
+    _indexopts_set_try_decrypt.restype = None
+
+    _indexopts_destroy = nmlib.notmuch_indexopts_destroy
+    _indexopts_destroy.argtypes = [NotmuchIndexoptsP]
+    _indexopts_destroy.restype = None
+
     _index_file = nmlib.notmuch_database_index_file
     _index_file.argtypes = [NotmuchDatabaseP, c_char_p,
                              c_void_p,
                              POINTER(NotmuchMessageP)]
     _index_file.restype = c_uint
 
-    def index_file(self, filename, sync_maildir_flags=False):
+    def index_file(self, filename, sync_maildir_flags=False, try_decrypt=None):
         """Adds a new message to the database
 
         :param filename: should be a path relative to the path of the
@@ -427,6 +443,23 @@ class Database(object):
             API. You might want to look into the underlying method
             :meth:`Message.maildir_flags_to_tags`.
 
+        :param try_decrypt: If the message contains any encrypted
+            parts, and try_decrypt is set to
+            :attr:`DECRYPTION_POLICY`.TRUE, notmuch will try to
+            decrypt the message and index the cleartext, stashing any
+            discovered session keys.  If it is set to
+            :attr:`DECRYPTION_POLICY`.FALSE, it will never try to
+            decrypt during indexing.  If it is set to
+            :attr:`DECRYPTION_POLICY`.AUTO, then it will try to use
+            any stashed session keys it knows about, but will not try
+            to access the user's secret keys.
+            :attr:`DECRYPTION_POLICY`.NOSTASH behaves the same as
+            :attr:`DECRYPTION_POLICY`.TRUE except that no session keys
+            are stashed in the database.  If try_decrypt is set to
+            None (the default), then the database itself will decide
+            whether to decrypt, based on the `index.try_decrypt`
+            configuration setting (see notmuch-config(1)).
+
         :returns: On success, we return
 
            1) a :class:`Message` object that can be used for things
@@ -454,10 +487,19 @@ class Database(object):
               :attr:`STATUS`.READ_ONLY_DATABASE
                       Database was opened in read-only mode so no message can
                       be added.
+
         """
         self._assert_db_is_initialized()
         msg_p = NotmuchMessageP()
-        status = self._index_file(self._db, _str(filename), c_void_p(None), byref(msg_p))
+        indexopts = c_void_p(None)
+        if try_decrypt is not None:
+            indexopts = self._get_default_indexopts(self._db)
+            self._indexopts_set_try_decrypt(indexopts, try_decrypt)
+
+        status = self._index_file(self._db, _str(filename), indexopts, byref(msg_p))
+
+        if indexopts:
+            self._indexopts_destroy(indexopts)
 
         if not status in [STATUS.SUCCESS, STATUS.DUPLICATE_MESSAGE_ID]:
             raise NotmuchError(status)
diff --git a/bindings/python/notmuch/globals.py b/bindings/python/notmuch/globals.py
index b1eec2cf..71426c84 100644
--- a/bindings/python/notmuch/globals.py
+++ b/bindings/python/notmuch/globals.py
@@ -88,3 +88,8 @@ NotmuchDirectoryP = POINTER(NotmuchDirectoryS)
 class NotmuchFilenamesS(Structure):
     pass
 NotmuchFilenamesP = POINTER(NotmuchFilenamesS)
+
+
+class NotmuchIndexoptsS(Structure):
+    pass
+NotmuchIndexoptsP = POINTER(NotmuchIndexoptsS)
--
2.14.2

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Daniel Kahn Gillmor Daniel Kahn Gillmor
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Re: [PATCH 16/18] crypto: add --try-decrypt=nostash to avoid stashing session keys

In reply to this post by Daniel Kahn Gillmor
On Wed 2017-10-25 02:52:01 -0400, Daniel Kahn Gillmor wrote:
> -        DO NOT USE ``index.try_decrypt=true`` without considering the
> -        security of your index.
> +        DO NOT USE ``index.try_decrypt=true`` or ``index-only``
> +        without considering the security of your index.

jrollins helpfully caught that i'd let the previous, worse name of
"nostash" ("index-only") sneak into this commit.  I've fixed it in my
local copy of this branch, which can be found as "session-keys" at
https://gitlab.com/dkg/notmuch (current commit ID
ac7a7bb931b68a17dff0b4b782a2bdeced4e779c)

I'll wait to send revised patches to the list once i've incorporated any
other reviews folks want to send my way.

      --dkg

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