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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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11
g10/ChangeLog
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@ -1,5 +1,12 @@
2007-11-28 David Shaw <dshaw@jabberwocky.com> 2007-11-28 David Shaw <dshaw@jabberwocky.com>
* sig-check.c (do_check): Code to try both the incorrect and
correct 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.
* gpg.c (print_algo_names): New. * gpg.c (print_algo_names): New.
(list_config): Use it here for the "ciphername" and "digestname" (list_config): Use it here for the "ciphername" and "digestname"
config items so we can get a script-parseable list of the names. config items so we can get a script-parseable list of the names.
@ -13210,8 +13217,8 @@ Thu Feb 12 22:24:42 1998 Werner Koch (wk@frodo)
* pubkey-enc.c (get_session_key): rewritten * pubkey-enc.c (get_session_key): rewritten
Copyright 1998, 1999, 2000, 2001, 2002, 2003, Copyright 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006,
2004, 2005, 2006 Free Software Foundation, Inc. 2007 Free Software Foundation, Inc.
This file is free software; as a special exception the author gives This file is free software; as a special exception the author gives
unlimited permission to copy and/or distribute it, with or without unlimited permission to copy and/or distribute it, with or without

6
g10/main.h
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@ -1,6 +1,6 @@
/* main.h /* main.h
* Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, * Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006,
* 2006 Free Software Foundation, Inc. * 2007 Free Software Foundation, Inc.
* *
* This file is part of GnuPG. * This file is part of GnuPG.
* *
@ -200,6 +200,8 @@ void try_make_homedir( const char *fname );
/*-- seskey.c --*/ /*-- seskey.c --*/
void make_session_key( DEK *dek ); void make_session_key( DEK *dek );
MPI encode_session_key( DEK *dek, unsigned nbits ); MPI encode_session_key( DEK *dek, unsigned nbits );
MPI pkcs1_encode_md( MD_HANDLE md, int algo, size_t len, unsigned nbits,
const byte *asn, size_t asnlen );
MPI encode_md_value( PKT_public_key *pk, PKT_secret_key *sk, MPI encode_md_value( PKT_public_key *pk, PKT_secret_key *sk,
MD_HANDLE md, int hash_algo ); MD_HANDLE md, int hash_algo );

18
g10/seskey.c
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@ -1,6 +1,6 @@
/* seskey.c - make sesssion keys etc. /* seskey.c - make sesssion keys etc.
* Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003, 2004, * Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2006,
* 2006 Free Software Foundation, Inc. * 2007 Free Software Foundation, Inc.
* *
* This file is part of GnuPG. * This file is part of GnuPG.
* *
@ -29,7 +29,6 @@
#include "main.h" #include "main.h"
#include "i18n.h" #include "i18n.h"
/**************** /****************
* Make a session key and put it into DEK * Make a session key and put it into DEK
*/ */
@ -142,10 +141,9 @@ encode_session_key( DEK *dek, unsigned nbits )
return a; return a;
} }
MPI
static MPI pkcs1_encode_md( MD_HANDLE md, int algo, size_t len, unsigned nbits,
do_encode_md( MD_HANDLE md, int algo, size_t len, unsigned nbits, const byte *asn, size_t asnlen )
const byte *asn, size_t asnlen )
{ {
int nframe = (nbits+7) / 8; int nframe = (nbits+7) / 8;
byte *frame; byte *frame;
@ -260,9 +258,9 @@ encode_md_value( PKT_public_key *pk, PKT_secret_key *sk,
size_t asnlen,mdlen; size_t asnlen,mdlen;
asn = md_asn_oid( hash_algo, &asnlen, &mdlen ); asn = md_asn_oid( hash_algo, &asnlen, &mdlen );
frame = do_encode_md( md, hash_algo, mdlen, frame = pkcs1_encode_md( md, hash_algo, mdlen,
mpi_get_nbits(pk?pk->pkey[0]:sk->skey[0]), mpi_get_nbits(pk?pk->pkey[0]:sk->skey[0]),
asn, asnlen ); asn, asnlen );
} }
return frame; return frame;

30
g10/sig-check.c
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@ -1,6 +1,6 @@
/* sig-check.c - Check a signature /* sig-check.c - Check a signature
* Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003, * Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006,
* 2004 Free Software Foundation, Inc. * 2007 Free Software Foundation, Inc.
* *
* This file is part of GnuPG. * 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 ); rc = pubkey_verify( pk->pubkey_algo, result, sig->data, pk->pkey );
mpi_free( result ); 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 ) if( !rc && sig->flags.unknown_critical )
{ {
log_info(_("assuming bad signature from key %s" log_info(_("assuming bad signature from key %s"