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* sig-check.c (do_check): Code to try both the incorrect and correct

Browse source 
SHA-224 DER prefixes when verifying a signature.  See the change
itself for more discussion.

* main.h, seskey.c (do_encode_md): Rename to pkcs1_encode_md and make
non-static.
This commit is contained in:
David Shaw 2007-11-28 23:08:35 +00:00
parent 154407fd38
commit a92fa61c48
4 changed files with 49 additions and 16 deletions
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30
g10/sig-check.c
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@ -1,6 +1,6 @@
/* sig-check.c - Check a signature
* Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003,
* 2004 Free Software Foundation, Inc.
* Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006,
* 2007 Free Software Foundation, Inc.
*
* This file is part of GnuPG.
*
@ -280,6 +280,32 @@ do_check( PKT_public_key *pk, PKT_signature *sig, MD_HANDLE digest,
rc = pubkey_verify( pk->pubkey_algo, result, sig->data, pk->pkey );
mpi_free( result );
if(rc==G10ERR_BAD_SIGN && is_RSA(pk->pubkey_algo)
&& sig->digest_algo==DIGEST_ALGO_SHA224)
{
/* This code is to work around a SHA-224 problem. RFC-4880
and the drafts leading up to it were published with the
wrong DER prefix for SHA-224. Unfortunately, GPG pre-1.4.8
used this wrong prefix. What this code does is take all
bad RSA signatures that use SHA-224, and re-checks them
using the old, incorrect, DER prefix. Someday we should
remove this code, and when we do remove it, pkcs1_encode_md
can be made into a static function again. Note that GPG2
does not have this issue as it uses libgcrypt, which is
being fixed while it is still a development version. */
/* The incorrect SHA-224 DER prefix used in pre-1.4.8 */
static byte asn[]={0x30, 0x31, 0x30, 0x0d, 0x06, 0x09, 0x60, 0x86,
0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x04, 0x05,
0x00, 0x04, 0x20};
result=pkcs1_encode_md(digest,DIGEST_ALGO_SHA224,28,
mpi_get_nbits(pk->pkey[0]),asn,DIM(asn));
rc=pubkey_verify(pk->pubkey_algo,result,sig->data,pk->pkey);
mpi_free(result);
}
if( !rc && sig->flags.unknown_critical )
{
log_info(_("assuming bad signature from key %s"