gpg: Improve passphrase caching.

* agent/cache.c (last_stored_cache_key): New.
(agent_get_cache): Allow NULL for KEY.
(agent_store_cache_hit): New.
* agent/findkey.c (unprotect): Call new function and try to use the
last stored key.

* g10/revoke.c (create_revocation): Add arg CACHE_NONCE and pass to
make_keysig_packet.
(gen_standard_revoke): Add arg CACHE_NONCE and pass to
create_revocation.
* g10/keygen.c (do_generate_keypair): Call gen_standard_revoke with
cache nonce.
--

This patch adds two features:

1. The key for the last passphrase successfully used for unprotecting
a key is stored away.  On a cache miss the stored away passphrase is
tried as well.  This helps for the common GPG use case of having a
signing and encryption (sub)key with the same passphrase.  See the
code for more comments.

2. The now auto-generated revocation certificate does not anymore
popup a passphrase prompt.  Thus for standard key generation the
passphrase needs to be given only once (well, two with the
confirmation).

1 files changed, 28 insertions, 1 deletions

diff --git a/agent/cache.c b/agent/cache.c
index d4deaeb8c..49402e434 100644
--- a/agent/cache.c
+++ b/agent/cache.c
@@ -65,6 +65,9 @@ struct cache_item_s {
 /* The cache himself.  */
 static ITEM thecache;
 
+/* NULL or the last cache key stored by agent_store_cache_hit.  */
+static char *last_stored_cache_key;
+
 
 /* This function must be called once to initialize this module. It
    has to be done before a second thread is spawned.  */
@@ -388,12 +391,24 @@ agent_get_cache (const char *key, cache_mode_t cache_mode)
   ITEM r;
   char *value = NULL;
   int res;
+  int last_stored = 0;
 
   if (cache_mode == CACHE_MODE_IGNORE)
     return NULL;
 
+  if (!key)
+    {
+      key = last_stored_cache_key;
+      if (!key)
+        return NULL;
+      last_stored = 1;
+    }
+
+
   if (DBG_CACHE)
-    log_debug ("agent_get_cache '%s' (mode %d) ...\n", key, cache_mode);
+    log_debug ("agent_get_cache '%s' (mode %d)%s ...\n",
+               key, cache_mode,
+               last_stored? " (stored cache key)":"");
   housekeeping ();
 
   for (r=thecache; r; r = r->next)
@@ -404,6 +419,7 @@ agent_get_cache (const char *key, cache_mode_t cache_mode)
               || r->cache_mode == cache_mode)
           && !strcmp (r->key, key))
         {
+          /* Note: To avoid races KEY may not be accessed anymore below.  */
           r->accessed = gnupg_get_time ();
           if (DBG_CACHE)
             log_debug ("... hit\n");
@@ -442,3 +458,14 @@ agent_get_cache (const char *key, cache_mode_t cache_mode)
 
   return NULL;
 }
+
+
+/* Store the key for the last successful cache hit.  That value is
+   used by agent_get_cache if the requested KEY is given as NULL.
+   NULL may be used to remove that key. */
+void
+agent_store_cache_hit (const char *key)
+{
+  xfree (last_stored_cache_key);
+  last_stored_cache_key = key? xtrystrdup (key) : NULL;
+}