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-rw-r--r--g10/seskey.c244
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diff --git a/g10/seskey.c b/g10/seskey.c
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-/* seskey.c - make sesssion keys etc.
- * Copyright (C) 1998, 1999, 2000, 2001, 2003 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 2 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, write to the Free Software
- * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
- */
-
-#include <config.h>
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
-#include <assert.h>
-
-#include "gpg.h"
-#include "util.h"
-#include "cipher.h"
-#include "mpi.h"
-#include "main.h"
-#include "i18n.h"
-#include "options.h"
-
-/****************
- * Make a session key and put it into DEK
- */
-void
-make_session_key( DEK *dek )
-{
- gcry_cipher_hd_t chd;
- int i, rc;
-
- dek->keylen = gcry_cipher_get_algo_keylen (dek->algo);
-
- if (gcry_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. NBITS is the number of bits which should be used
- * for packing the session key.
- * returns: A mpi with the session key (caller must free)
- */
-gcry_mpi_t
-encode_session_key (DEK *dek, unsigned int nbits)
-{
- int nframe = (nbits+7) / 8;
- byte *p;
- byte *frame;
- int i,n;
- u16 csum;
- gcry_mpi_t 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 in this way:
- *
- * 0 2 RND(n 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 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
- */
- csum = 0;
- for( p = dek->key, i=0; i < dek->keylen; i++ )
- csum += *p++;
-
- frame = gcry_xmalloc_secure ( nframe );
- n = 0;
- frame[n++] = 0;
- frame[n++] = 2;
- i = nframe - 6 - dek->keylen;
- 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; /* better get some more */
- pp = gcry_random_bytes_secure( k, GCRY_STRONG_RANDOM);
- for(j=0; j < i && k ; j++ )
- if( !p[j] )
- p[j] = pp[--k];
- 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;
- assert (n == nframe);
-
- if (DBG_CIPHER)
- log_printhex ("encoded session key:", frame, 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, int v3compathack )
-{
- int nframe = (nbits+7) / 8;
- byte *frame;
- int i,n;
- gcry_mpi_t a;
-
- if( len + asnlen + 4 > nframe )
- log_bug("can't encode a %d bit MD into a %d bits frame\n",
- (int)(len*8), (int)nbits);
-
- /* We encode the MD in this way:
- *
- * 0 A 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++] = v3compathack? algo : 1; /* block type */
- i = nframe - len - asnlen -3 ;
- 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;
- assert( n == nframe );
- if (gcry_mpi_scan( &a, GCRYMPI_FMT_USG, frame, n, &nframe ))
- BUG();
- xfree (frame);
- return a;
-}
-
-
-/****************
- * Encode a message digest into an MPI.
- * v3compathack is used to work around a bug in old GnuPG versions
- * which did put the algo identifier inseatd of the block type 1 into
- * the encoded value. Setting this flag forces the old behaviour.
- */
-gcry_mpi_t
-encode_md_value (int pubkey_algo, gcry_md_hd_t md, int hash_algo,
- unsigned int nbits, int v3compathack )
-{
- int algo = hash_algo? hash_algo : gcry_md_get_algo (md);
- gcry_mpi_t frame;
-
- if (pubkey_algo == GCRY_PK_DSA)
- {
- size_t n = gcry_md_get_algo_dlen(hash_algo);
- if (n != 20)
- {
- log_error (_("DSA requires the use of a 160 bit hash algorithm\n"));
- return NULL;
- }
- if (gcry_mpi_scan( &frame, GCRYMPI_FMT_USG,
- gcry_md_read (md, hash_algo), n, &n ) )
- BUG();
- }
- else
- {
- gpg_error_t rc;
- byte *asn;
- size_t asnlen;
-
- rc = gcry_md_algo_info( algo, GCRYCTL_GET_ASNOID, NULL, &asnlen);
- if (rc)
- log_fatal("can't get OID of algo %d: %s\n",
- algo, gpg_strerror (rc));
- asn = xmalloc (asnlen);
- if( gcry_md_algo_info( algo, GCRYCTL_GET_ASNOID, asn, &asnlen ) )
- BUG();
- frame = do_encode_md( md, algo, gcry_md_get_algo_dlen( algo ),
- nbits, asn, asnlen, v3compathack );
- xfree (asn);
- }
- return frame;
-}
-
-
-
-
-
-
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