crypto: add --decrypt=nostash to avoid stashing session keys

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

@@ -288,7 +288,7 @@ _notmuch_insert()
 	    return
 	    ;;
 	--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
 	--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
 	--decrypt)
-	    COMPREPLY=( $( compgen -W "true false auto" -- "${cur}" ) )
+	    COMPREPLY=( $( compgen -W "true false auto nostash" -- "${cur}" ) )
 	    return
 	    ;;
     esac

doc/man1/notmuch-config.rst

@@ -141,6 +141,9 @@ The available configuration items are described below.
     **index.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 +153,15 @@ The available configuration items are described below.
         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
-        ensure that the notmuch message index is adequately protected.
-        DO NOT USE ``index.decrypt=true`` without considering the
-        security of your index.
+        ``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 (and a
+        stashed session key is certainly sufficient) to reconstruct
+        the cleartext of the message itself, so please ensure that the
+        notmuch message index is adequately protected.  DO NOT USE
+        ``index.decrypt=true`` or ``index.decrypt=nostash`` without
+        considering the security of your index.
 
         Default: ``auto``.
 

doc/man1/notmuch-insert.rst

@@ -51,10 +51,10 @@ Supported options for **insert** include
     ``--no-hooks``
         Prevent hooks from being run.
 
-    ``--decrypt=(true|auto|false)``
+    ``--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
@@ -62,11 +62,15 @@ Supported options for **insert** include
         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
+        ``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 (and a stashed
+        session key is certainly sufficient) to reconstruct the
+        cleartext of the message itself, so please ensure that the
         notmuch message index is adequately protected. DO NOT USE
-        ``--decrypt=true`` without considering the security of
-        your index.
+        ``--decrypt=true`` or ``--decrypt=nostash`` without
+        considering the security of your index.
 
         See also ``index.decrypt`` in **notmuch-config(1)**.
 

doc/man1/notmuch-new.rst

@@ -43,10 +43,10 @@ Supported options for **new** include
     ``--quiet``
         Do not print progress or results.
 
-    ``--decrypt=(true|auto|false)``
+    ``--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
@@ -56,7 +56,8 @@ Supported options for **new** include
         key is certainly sufficient) to reconstruct the cleartext of
         the message itself, so please ensure that the notmuch message
         index is adequately protected.  DO NOT USE ``--decrypt=true``
-        without considering the security of your index.
+        or ``--decrypt=nostash`` without considering the security of
+        your index.
 
         See also ``index.decrypt`` in **notmuch-config(1)**.
 

doc/man1/notmuch-reindex.rst

@@ -21,23 +21,27 @@ messages using the supplied options.
 
 Supported options for **reindex** include
 
-    ``--decrypt=(true|auto|false)``
+    ``--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
+        Be aware that the index is likely sufficient (and a stashed
+        session key is certainly sufficient) to reconstruct the
+        cleartext of the message itself, so please ensure that the
         notmuch message index is adequately protected. DO NOT USE
-        ``--decrypt=true`` without considering the security of your
-        index.
+        ``--decrypt=true`` or ``--decrypt=nostash`` without
+        considering the security of your index.
 
         See also ``index.decrypt`` in **notmuch-config(1)**.
 

lib/indexopts.c

@@ -42,6 +42,8 @@ notmuch_database_get_default_indexopts (notmuch_database_t *db)
 		 (!(strcasecmp(decrypt_policy, "no"))) ||
 		 (!(strcasecmp(decrypt_policy, "0"))))
 	    notmuch_indexopts_set_decrypt_policy (ret, NOTMUCH_DECRYPT_FALSE);
+	else if (!strcasecmp(decrypt_policy, "nostash"))
+	    notmuch_indexopts_set_decrypt_policy (ret, NOTMUCH_DECRYPT_NOSTASH);
     }
 
     free (decrypt_policy);

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;
 
 /**

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 ();
 

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 {

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 = "decrypt" },
     { }

test/T357-index-decryption.sh

@@ -188,6 +188,29 @@ test_expect_equal \
     "$output" \
     "$expected"
 
+test_begin_subtest "index cleartext without keeping session keys"
+test_expect_success "notmuch reindex --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"

util/crypto.c

@@ -199,7 +199,7 @@ _notmuch_crypto_decrypt (bool *attempted,
 #if (GMIME_MAJOR_VERSION < 3)
 #if HAVE_GMIME_SESSION_KEYS
     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);
@@ -212,7 +212,7 @@ _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);