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gpg: Fail decryption for AES etc message w/o MDC.

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* g10/mainproc.c (proc_encrypted): Fail for modern messages w/o MDC.
--

This change turns the missing MDC warning into an error if the message
has been encrypted using a cipher with a non-64 bit block length cipher
and it is not Twofish.

We can assume that such messages are created by code which should have
been able to create MDC packets.  AES was introduced with 1.0.3 on
2000-09-18 shortly after MDC (1.0.2 on 2000-07-12).  We need to
exclude Twofish because that might have been used before MDC.

Signed-off-by: Werner Koch <wk@gnupg.org>
This commit is contained in:
Werner Koch 2015-10-06 09:40:57 +02:00
parent 4a5bd1720f
commit 625e292108
No known key found for this signature in database
GPG Key ID: E3FDFF218E45B72B
1 changed files with 16 additions and 0 deletions
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16
g10/mainproc.c
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@ -607,6 +607,22 @@ proc_encrypted (CTX c, PACKET *pkt)
if (result == -1) if (result == -1)
; ;
else if (!result
&& !opt.ignore_mdc_error
&& !pkt->pkt.encrypted->mdc_method
&& openpgp_cipher_get_algo_blklen (c->dek->algo) != 8
&& c->dek->algo != CIPHER_ALGO_TWOFISH)
{
/* The message has been decrypted but has no MDC despite that a
modern cipher (blocklength != 64 bit, except for Twofish) is
used and the option to ignore MDC errors is not used: To
avoid attacks changing an MDC message to a non-MDC message,
we fail here. */
log_error (_("WARNING: message was not integrity protected\n"));
if (opt.verbose > 1)
log_info ("decryption forced to fail\n");
write_status (STATUS_DECRYPTION_FAILED);
}
else if (!result || (gpg_err_code (result) == GPG_ERR_BAD_SIGNATURE else if (!result || (gpg_err_code (result) == GPG_ERR_BAD_SIGNATURE
&& opt.ignore_mdc_error)) && opt.ignore_mdc_error))
{ {