gpg: Distinguish between missing and cleared key flags.

* include/cipher.h (PUBKEY_USAGE_NONE): New.
* g10/getkey.c (parse_key_usage): Set new flag.
--

We do not want to use the default capabilities (derived from the
algorithm) if any key flags are given in a signature.  Thus if key
flags are used in any way, the default key capabilities are never
used.

This allows to create a key with key flags set to all zero so it can't
be used.  This better reflects common sense.

1 files changed, 7 insertions, 1 deletions

diff --git a/g10/getkey.c b/g10/getkey.c
index 929427302..8cc560100 100644
--- a/g10/getkey.c
+++ b/g10/getkey.c
@@ -1276,13 +1276,19 @@ parse_key_usage (PKT_signature * sig)
 
       if (flags)
 	key_usage |= PUBKEY_USAGE_UNKNOWN;
+
+      if (!key_usage)
+	key_usage |= PUBKEY_USAGE_NONE;
     }
+  else if (p) /* Key flags of length zero.  */
+    key_usage |= PUBKEY_USAGE_NONE;
 
   /* We set PUBKEY_USAGE_UNKNOWN to indicate that this key has a
      capability that we do not handle.  This serves to distinguish
      between a zero key usage which we handle as the default
      capabilities for that algorithm, and a usage that we do not
-     handle. */
+     handle.  Likewise we use PUBKEY_USAGE_NONE to indicate that
+     key_flags have been given but they do not specify any usage.  */
 
   return key_usage;
 }