mirror of git://git.gnupg.org/gnupg.git
360 lines
11 KiB
C
360 lines
11 KiB
C
/* seskey.c - make session keys etc.
|
|
* Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003, 2004,
|
|
* 2006, 2009, 2010 Free Software Foundation, Inc.
|
|
*
|
|
* This file is part of GnuPG.
|
|
*
|
|
* GnuPG is free software; you can redistribute it and/or modify
|
|
* it under the terms of the GNU General Public License as published by
|
|
* the Free Software Foundation; either version 3 of the License, or
|
|
* (at your option) any later version.
|
|
*
|
|
* GnuPG is distributed in the hope that it will be useful,
|
|
* but WITHOUT ANY WARRANTY; without even the implied warranty of
|
|
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
|
|
* GNU General Public License for more details.
|
|
*
|
|
* You should have received a copy of the GNU General Public License
|
|
* along with this program; if not, see <https://www.gnu.org/licenses/>.
|
|
*/
|
|
|
|
#include <config.h>
|
|
#include <stdio.h>
|
|
#include <stdlib.h>
|
|
#include <string.h>
|
|
|
|
#include "gpg.h"
|
|
#include "../common/util.h"
|
|
#include "options.h"
|
|
#include "main.h"
|
|
#include "../common/i18n.h"
|
|
|
|
|
|
/* Generate a new session key in *DEK that is appropriate for the
|
|
* algorithm DEK->ALGO (i.e., ensure that the key is not weak).
|
|
*
|
|
* This function overwrites DEK->KEYLEN, DEK->KEY. The rest of the
|
|
* fields are left as is. */
|
|
void
|
|
make_session_key( DEK *dek )
|
|
{
|
|
gcry_cipher_hd_t chd;
|
|
int i, rc;
|
|
|
|
dek->keylen = openpgp_cipher_get_algo_keylen (dek->algo);
|
|
|
|
if (openpgp_cipher_open (&chd, dek->algo, GCRY_CIPHER_MODE_CFB,
|
|
(GCRY_CIPHER_SECURE
|
|
| (dek->algo >= 100 ?
|
|
0 : GCRY_CIPHER_ENABLE_SYNC))) )
|
|
BUG();
|
|
gcry_randomize (dek->key, dek->keylen, GCRY_STRONG_RANDOM );
|
|
for (i=0; i < 16; i++ )
|
|
{
|
|
rc = gcry_cipher_setkey (chd, dek->key, dek->keylen);
|
|
if (!rc)
|
|
{
|
|
gcry_cipher_close (chd);
|
|
return;
|
|
}
|
|
if (gpg_err_code (rc) != GPG_ERR_WEAK_KEY)
|
|
BUG();
|
|
log_info(_("weak key created - retrying\n") );
|
|
/* Renew the session key until we get a non-weak key. */
|
|
gcry_randomize (dek->key, dek->keylen, GCRY_STRONG_RANDOM);
|
|
}
|
|
log_fatal (_("cannot avoid weak key for symmetric cipher; "
|
|
"tried %d times!\n"), i);
|
|
}
|
|
|
|
|
|
/* Encode the session key stored in DEK as an MPI in preparation to
|
|
* encrypt it with the public key algorithm OPENPGP_PK_ALGO with a key
|
|
* whose length (the size of the public key) is NBITS.
|
|
*
|
|
* On success, returns an MPI, which the caller must free using
|
|
* gcry_mpi_release(). */
|
|
gcry_mpi_t
|
|
encode_session_key (int openpgp_pk_algo, DEK *dek, unsigned int nbits)
|
|
{
|
|
size_t nframe = (nbits+7) / 8;
|
|
byte *p;
|
|
byte *frame;
|
|
int i,n;
|
|
u16 csum;
|
|
gcry_mpi_t a;
|
|
|
|
if (DBG_CRYPTO)
|
|
log_debug ("encode_session_key: encoding %d byte DEK", dek->keylen);
|
|
|
|
csum = 0;
|
|
for (p = dek->key, i=0; i < dek->keylen; i++)
|
|
csum += *p++;
|
|
|
|
/* Shortcut for ECDH. It's padding is minimal to simply make the
|
|
output be a multiple of 8 bytes. */
|
|
if (openpgp_pk_algo == PUBKEY_ALGO_ECDH)
|
|
{
|
|
/* Pad to 8 byte granulatiry; the padding byte is the number of
|
|
* padded bytes.
|
|
*
|
|
* A DEK(k bytes) CSUM(2 bytes) 0x 0x 0x 0x ... 0x
|
|
* +---- x times ---+
|
|
*/
|
|
nframe = (( 1 + dek->keylen + 2 /* The value so far is always odd. */
|
|
+ 7 ) & (~7));
|
|
|
|
/* alg+key+csum fit and the size is congruent to 8. */
|
|
log_assert (!(nframe%8) && nframe > 1 + dek->keylen + 2 );
|
|
|
|
frame = xmalloc_secure (nframe);
|
|
n = 0;
|
|
frame[n++] = dek->algo;
|
|
memcpy (frame+n, dek->key, dek->keylen);
|
|
n += dek->keylen;
|
|
frame[n++] = csum >> 8;
|
|
frame[n++] = csum;
|
|
i = nframe - n; /* Number of padded bytes. */
|
|
memset (frame+n, i, i); /* Use it as the value of each padded byte. */
|
|
log_assert (n+i == nframe);
|
|
|
|
if (DBG_CRYPTO)
|
|
log_debug ("encode_session_key: "
|
|
"[%d] %02x %02x %02x ... %02x %02x %02x\n",
|
|
(int) nframe, frame[0], frame[1], frame[2],
|
|
frame[nframe-3], frame[nframe-2], frame[nframe-1]);
|
|
|
|
if (gcry_mpi_scan (&a, GCRYMPI_FMT_USG, frame, nframe, &nframe))
|
|
BUG();
|
|
xfree(frame);
|
|
return a;
|
|
}
|
|
|
|
/* The current limitation is that we can only use a session key
|
|
* whose length is a multiple of BITS_PER_MPI_LIMB
|
|
* I think we can live with that.
|
|
*/
|
|
if (dek->keylen + 7 > nframe || !nframe)
|
|
log_bug ("can't encode a %d bit key in a %d bits frame\n",
|
|
dek->keylen*8, nbits );
|
|
|
|
/* We encode the session key according to PKCS#1 v1.5 (see section
|
|
* 13.1.1 of RFC 4880):
|
|
*
|
|
* 0 2 RND(i bytes) 0 A DEK(k bytes) CSUM(2 bytes)
|
|
*
|
|
* (But how can we store the leading 0 - the external representaion
|
|
* of MPIs doesn't allow leading zeroes =:-)
|
|
*
|
|
* RND are (at least 1) non-zero random bytes.
|
|
* A is the cipher algorithm
|
|
* DEK is the encryption key (session key) length k depends on the
|
|
* cipher algorithm (20 is used with blowfish160).
|
|
* CSUM is the 16 bit checksum over the DEK
|
|
*/
|
|
|
|
frame = xmalloc_secure( nframe );
|
|
n = 0;
|
|
frame[n++] = 0;
|
|
frame[n++] = 2;
|
|
/* The number of random bytes are the number of otherwise unused
|
|
bytes. See diagram above. */
|
|
i = nframe - 6 - dek->keylen;
|
|
log_assert( i > 0 );
|
|
p = gcry_random_bytes_secure (i, GCRY_STRONG_RANDOM);
|
|
/* Replace zero bytes by new values. */
|
|
for (;;)
|
|
{
|
|
int j, k;
|
|
byte *pp;
|
|
|
|
/* Count the zero bytes. */
|
|
for (j=k=0; j < i; j++ )
|
|
if (!p[j])
|
|
k++;
|
|
if (!k)
|
|
break; /* Okay: no zero bytes. */
|
|
k += k/128 + 3; /* Better get some more. */
|
|
pp = gcry_random_bytes_secure (k, GCRY_STRONG_RANDOM);
|
|
for (j=0; j < i && k ;)
|
|
{
|
|
if (!p[j])
|
|
p[j] = pp[--k];
|
|
if (p[j])
|
|
j++;
|
|
}
|
|
xfree (pp);
|
|
}
|
|
memcpy (frame+n, p, i);
|
|
xfree (p);
|
|
n += i;
|
|
frame[n++] = 0;
|
|
frame[n++] = dek->algo;
|
|
memcpy (frame+n, dek->key, dek->keylen );
|
|
n += dek->keylen;
|
|
frame[n++] = csum >>8;
|
|
frame[n++] = csum;
|
|
log_assert (n == nframe);
|
|
if (gcry_mpi_scan( &a, GCRYMPI_FMT_USG, frame, n, &nframe))
|
|
BUG();
|
|
xfree (frame);
|
|
return a;
|
|
}
|
|
|
|
|
|
static gcry_mpi_t
|
|
do_encode_md( gcry_md_hd_t md, int algo, size_t len, unsigned nbits,
|
|
const byte *asn, size_t asnlen )
|
|
{
|
|
size_t nframe = (nbits+7) / 8;
|
|
byte *frame;
|
|
int i,n;
|
|
gcry_mpi_t a;
|
|
|
|
if (len + asnlen + 4 > nframe)
|
|
{
|
|
log_error ("can't encode a %d bit MD into a %d bits frame, algo=%d\n",
|
|
(int)(len*8), (int)nbits, algo);
|
|
return NULL;
|
|
}
|
|
|
|
/* We encode the MD in this way:
|
|
*
|
|
* 0 1 PAD(n bytes) 0 ASN(asnlen bytes) MD(len bytes)
|
|
*
|
|
* PAD consists of FF bytes.
|
|
*/
|
|
frame = gcry_md_is_secure (md)? xmalloc_secure (nframe) : xmalloc (nframe);
|
|
n = 0;
|
|
frame[n++] = 0;
|
|
frame[n++] = 1; /* block type */
|
|
i = nframe - len - asnlen -3 ;
|
|
log_assert( i > 1 );
|
|
memset( frame+n, 0xff, i ); n += i;
|
|
frame[n++] = 0;
|
|
memcpy( frame+n, asn, asnlen ); n += asnlen;
|
|
memcpy( frame+n, gcry_md_read (md, algo), len ); n += len;
|
|
log_assert( n == nframe );
|
|
|
|
if (gcry_mpi_scan( &a, GCRYMPI_FMT_USG, frame, n, &nframe ))
|
|
BUG();
|
|
xfree(frame);
|
|
|
|
/* Note that PGP before version 2.3 encoded the MD as:
|
|
*
|
|
* 0 1 MD(16 bytes) 0 PAD(n bytes) 1
|
|
*
|
|
* The MD is always 16 bytes here because it's always MD5. We do
|
|
* not support pre-v2.3 signatures, but I'm including this comment
|
|
* so the information is easily found in the future.
|
|
*/
|
|
|
|
return a;
|
|
}
|
|
|
|
|
|
/****************
|
|
* Encode a message digest into an MPI.
|
|
* If it's for a DSA signature, make sure that the hash is large
|
|
* enough to fill up q. If the hash is too big, take the leftmost
|
|
* bits.
|
|
*/
|
|
gcry_mpi_t
|
|
encode_md_value (PKT_public_key *pk, gcry_md_hd_t md, int hash_algo)
|
|
{
|
|
gcry_mpi_t frame;
|
|
size_t mdlen;
|
|
|
|
log_assert (hash_algo);
|
|
log_assert (pk);
|
|
|
|
if (pk->pubkey_algo == PUBKEY_ALGO_EDDSA)
|
|
{
|
|
/* EdDSA signs data of arbitrary length. Thus no special
|
|
treatment is required. */
|
|
frame = gcry_mpi_set_opaque_copy (NULL, gcry_md_read (md, hash_algo),
|
|
8*gcry_md_get_algo_dlen (hash_algo));
|
|
}
|
|
else if (pk->pubkey_algo == PUBKEY_ALGO_DSA
|
|
|| pk->pubkey_algo == PUBKEY_ALGO_ECDSA)
|
|
{
|
|
/* It's a DSA signature, so find out the size of q. */
|
|
|
|
size_t qbits = gcry_mpi_get_nbits (pk->pkey[1]);
|
|
|
|
/* pkey[1] is Q for ECDSA, which is an uncompressed point,
|
|
i.e. 04 <x> <y> */
|
|
if (pk->pubkey_algo == PUBKEY_ALGO_ECDSA)
|
|
qbits = ecdsa_qbits_from_Q (qbits);
|
|
|
|
/* Make sure it is a multiple of 8 bits. */
|
|
if ((qbits%8))
|
|
{
|
|
log_error(_("DSA requires the hash length to be a"
|
|
" multiple of 8 bits\n"));
|
|
return NULL;
|
|
}
|
|
|
|
/* Don't allow any q smaller than 160 bits. This might need a
|
|
revisit as the DSA2 design firms up, but for now, we don't
|
|
want someone to issue signatures from a key with a 16-bit q
|
|
or something like that, which would look correct but allow
|
|
trivial forgeries. Yes, I know this rules out using MD5 with
|
|
DSA. ;) */
|
|
if (qbits < 160)
|
|
{
|
|
log_error (_("%s key %s uses an unsafe (%zu bit) hash\n"),
|
|
openpgp_pk_algo_name (pk->pubkey_algo),
|
|
keystr_from_pk (pk), qbits);
|
|
return NULL;
|
|
}
|
|
|
|
|
|
/* ECDSA 521 is special has it is larger than the largest hash
|
|
we have (SHA-512). Thus we change the size for further
|
|
processing to 512. */
|
|
if (pk->pubkey_algo == PUBKEY_ALGO_ECDSA && qbits > 512)
|
|
qbits = 512;
|
|
|
|
/* Check if we're too short. Too long is safe as we'll
|
|
automatically left-truncate. */
|
|
mdlen = gcry_md_get_algo_dlen (hash_algo);
|
|
if (mdlen < qbits/8)
|
|
{
|
|
log_error (_("%s key %s requires a %zu bit or larger hash "
|
|
"(hash is %s)\n"),
|
|
openpgp_pk_algo_name (pk->pubkey_algo),
|
|
keystr_from_pk (pk), qbits,
|
|
gcry_md_algo_name (hash_algo));
|
|
return NULL;
|
|
}
|
|
|
|
/* Note that we do the truncation by passing QBITS/8 as length to
|
|
mpi_scan. */
|
|
if (gcry_mpi_scan (&frame, GCRYMPI_FMT_USG,
|
|
gcry_md_read (md, hash_algo), qbits/8, NULL))
|
|
BUG();
|
|
}
|
|
else
|
|
{
|
|
gpg_error_t rc;
|
|
byte *asn;
|
|
size_t asnlen;
|
|
|
|
rc = gcry_md_algo_info (hash_algo, GCRYCTL_GET_ASNOID, NULL, &asnlen);
|
|
if (rc)
|
|
log_fatal ("can't get OID of digest algorithm %d: %s\n",
|
|
hash_algo, gpg_strerror (rc));
|
|
asn = xtrymalloc (asnlen);
|
|
if (!asn)
|
|
return NULL;
|
|
if ( gcry_md_algo_info (hash_algo, GCRYCTL_GET_ASNOID, asn, &asnlen) )
|
|
BUG();
|
|
frame = do_encode_md (md, hash_algo, gcry_md_get_algo_dlen (hash_algo),
|
|
gcry_mpi_get_nbits (pk->pkey[0]), asn, asnlen);
|
|
xfree (asn);
|
|
}
|
|
|
|
return frame;
|
|
}
|