Add API to support AEAD cipher modes

* cipher/cipher.c (_gcry_cipher_authenticate, _gcry_cipher_checktag)
(_gcry_cipher_gettag): New.
* doc/gcrypt.texi: Add documentation for new API functions.
* src/visibility.c (gcry_cipher_authenticate, gcry_cipher_checktag)
(gcry_cipher_gettag): New.
* src/gcrypt.h.in, src/visibility.h: add declarations of these
functions.
* src/libgcrypt.defs, src/libgcrypt.vers: export functions.
--

Authenticated Encryption with Associated Data (AEAD) cipher modes
provide authentication tag that can be used to authenticate message. At
the same time it allows one to specify additional (unencrypted data)
that will be authenticated together with the message. This class of
cipher modes requires additional API present in this commit.

This patch is based on original patch by Dmitry Eremin-Solenikov.

Changes in v2:
 - Change gcry_cipher_tag to gcry_cipher_checktag and gcry_cipher_gettag
   for giving tag (checktag) for decryption and reading tag (gettag) after
   encryption.
 - Change gcry_cipher_authenticate to gcry_cipher_setaad, since
   additional parameters needed for some AEAD modes (in this case CCM,
   which needs the length of encrypted data and tag for MAC
   initialization).
 - Add some documentation.

Changes in v3:
 - Change gcry_cipher_setaad back to gcry_cipher_authenticate. Additional
   parameters (encrypt_len, tag_len, aad_len) for CCM will be given
   through GCRY_CTL_SET_CCM_LENGTHS.

Changes in v4:
 - log_fatal => log_error

Signed-off-by: Jussi Kivilinna <jussi.kivilinna@iki.fi>

1 files changed, 11 insertions, 0 deletions

diff --git a/src/gcrypt.h.in b/src/gcrypt.h.in
index 64cc0e4e..f0ae927a 100644
--- a/src/gcrypt.h.in
+++ b/src/gcrypt.h.in
@@ -953,6 +953,17 @@ gcry_error_t gcry_cipher_setkey (gcry_cipher_hd_t hd,
 gcry_error_t gcry_cipher_setiv (gcry_cipher_hd_t hd,
                                 const void *iv, size_t ivlen);
 
+/* Provide additional authentication data for AEAD modes/ciphers.  */
+gcry_error_t gcry_cipher_authenticate (gcry_cipher_hd_t hd, const void *abuf,
+                                       size_t abuflen);
+
+/* Get authentication tag for AEAD modes/ciphers.  */
+gcry_error_t gcry_cipher_gettag (gcry_cipher_hd_t hd, void *outtag,
+                                 size_t taglen);
+
+/* Check authentication tag for AEAD modes/ciphers.  */
+gcry_error_t gcry_cipher_checktag (gcry_cipher_hd_t hd, const void *intag,
+                                   size_t taglen);
 
 /* Reset the handle to the state after open.  */
 #define gcry_cipher_reset(h)  gcry_cipher_ctl ((h), GCRYCTL_RESET, NULL, 0)