gpg: Implement AEAD for SKESK packets.

* g10/packet.h (PKT_symkey_enc): Add field aead_algo.
* g10/build-packet.c (do_symkey_enc): Support version 5 packets.
* g10/parse-packet.c (parse_symkeyenc): Ditto.
* g10/encrypt.c (encrypt_symmetric): Force using a random session
key in AEAD mode.
(encrypt_seskey): Add and support arg aead_algo.
(write_symkey_enc): Ditto.
(encrypt_simple): Adjust accordingly.
(encrypt_filter): Ditto.
* g10/gpgcompose.c (sk_esk): For now call encrypt_seskey without AEAD
support.
* g10/mainproc.c (symkey_decrypt_seskey): Support AEAD.  Nver call BUG
but return an error.
(proc_symkey_enc): Call symkey_decrypt_seskey in a bug compatible way.

* g10/import.c (check_prefs): Check AEAD preferences.
* g10/keyedit.c (show_prefs): Print AEAD preferences.
--

For easier debugging this patch also changes some diagnostics to also
print the encryption mode with the cipher algorithm.

Signed-off-by: Werner Koch <wk@gnupg.org>

1 files changed, 8 insertions, 5 deletions

diff --git a/g10/packet.h b/g10/packet.h
index 4d155746e..4f4569f66 100644
--- a/g10/packet.h
+++ b/g10/packet.h
@@ -94,12 +94,14 @@ typedef struct
 /* A symmetric-key encrypted session key packet as defined in RFC
    4880, Section 5.3.  All fields are serialized.  */
 typedef struct {
-  /* RFC 4880: this must be 4.  */
+  /* We support version 4 (rfc4880) and 5 (rfc4880bis).  */
   byte version;
-  /* The cipher algorithm used to encrypt the session key.  (This may
-     be different from the algorithm that is used to encrypt the SED
-     packet.)  */
+  /* The cipher algorithm used to encrypt the session key.  Note that
+   * this may be different from the algorithm that is used to encrypt
+   * bulk data.  */
   byte cipher_algo;
+  /* The AEAD algorithm or 0 for CFB encryption.  */
+  byte aead_algo;
   /* The string-to-key specifier.  */
   STRING2KEY s2k;
   /* The length of SESKEY in bytes or 0 if this packet does not
@@ -107,7 +109,8 @@ typedef struct {
      S2K function on the password is the session key. See RFC 4880,
      Section 5.3.)  */
   byte seskeylen;
-  /* The session key as encrypted by the S2K specifier.  */
+  /* The session key as encrypted by the S2K specifier.  For AEAD this
+   * includes the nonce and the authentication tag.  */
   byte seskey[1];
 } PKT_symkey_enc;