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/* seskey.c - make sesssion keys etc.
* Copyright (c) 1997 by Werner Koch (dd9jn)
*
* This file is part of G10.
*
* G10 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.
*
* G10 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 "util.h"
#include "cipher.h"
#include "mpi.h"
#include "main.h"
/****************
* Make a session key and put it into DEK
*/
void
make_session_key( DEK *dek )
{
switch( dek->algo ) {
case CIPHER_ALGO_BLOWFISH:
dek->keylen = 20;
randomize_buffer( dek->key, dek->keylen, 1 );
break;
case CIPHER_ALGO_BLOWFISH128:
dek->keylen = 16;
randomize_buffer( dek->key, dek->keylen, 1 );
break;
default: log_bug("invalid algo %d in make_session_key()\n");
}
}
/****************
* 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)
*/
MPI
encode_session_key( DEK *dek, unsigned nbits )
{
int nframe = (nbits+7) / 8;
byte *p;
MPI frame;
int i,n,c;
u16 csum;
/* the current limitation is, that we can only use a session key
* which length is a multiple of BITS_PER_MPI_LIMB
* I think we can live with that.
*/
if( dek->keylen + 7 > nframe || (nbits % BITS_PER_MPI_LIMB) || !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)
*
* 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 blowfish).
* CSUM is the 16 bit checksum over the DEK
*/
frame = mpi_alloc_secure( nframe / BYTES_PER_MPI_LIMB );
csum = 0;
for( p = dek->key, i=0; i < dek->keylen; i++ )
csum += *p++;
mpi_putbyte(frame, 0, csum );
mpi_putbyte(frame, 1, csum >> 8 );
for(n=2,i=dek->keylen-1, p = dek->key; i >= 0; i--, n++ )
mpi_putbyte(frame, n, p[i] );
mpi_putbyte(frame, n++, dek->algo );
mpi_putbyte(frame, n++, 0 );
while( n < nframe-2 ) {
while( !(c = get_random_byte(1)) )
;
mpi_putbyte(frame, n++, c );
}
mpi_putbyte(frame, n++, 2 );
mpi_putbyte(frame, n++, 0 );
assert( n == nframe );
return frame;
}
/****************
* Encode a ripemd160 message digest of LEN bytes into NBITS.
* returns: A mpi with the session key (caller must free)
* RMD160 Object ID is 1.3.36.3.2.1
*/
MPI
encode_rmd160_value( byte *md, unsigned len, unsigned nbits )
{
static byte asn[15] =
{ 0x30, 0x21, 0x30, 0x09, 0x06, 0x05, 0x2b, 0x24, 0x03,
0x02, 0x01, 0x05, 0x00, 0x04, 0x14 };
int nframe = (nbits+7) / 8;
byte *p;
MPI frame;
int i,n,c;
if( (nbits % BITS_PER_MPI_LIMB) || nframe < 42 || len != 20 )
log_bug("can't encode a %d bit MD into a %d bits frame\n",len*8, nbits);
/* We encode the MD in this way:
*
* 0 A PAD(n bytes) 0 ASN(15 bytes) MD(20 bytes)
*
* PAD consists of FF bytes.
*/
frame = mpi_alloc_secure( nframe / BYTES_PER_MPI_LIMB );
n = 0;
for(i=20-1; i >= 0; i--, n++ )
mpi_putbyte(frame, n, md[i] );
for( i=15-1; i >= 0; i--, n++ )
mpi_putbyte(frame, n, asn[i] );
mpi_putbyte(frame, n++, 0 );
while( n < nframe-2 )
mpi_putbyte(frame, n++, 0xff );
mpi_putbyte(frame, n++, DIGEST_ALGO_RMD160 );
mpi_putbyte(frame, n++, 0 );
assert( n == nframe );
return frame;
}
/****************
* Encode a sha-1 message digest of LEN bytes into NBITS.
* returns: A mpi with the session key (caller must free)
* SHA-1 Objet ID is 1.3.14.3.2.26
*/
MPI
encode_sha1_value( byte *md, unsigned len, unsigned nbits )
{
static byte asn[15] =
{ 0x30, 0x21, 0x30, 0x09, 0x06, 0x05, 0x2b, 0x0e, 0x03,
0x02, 0x1a, 0x05, 0x00, 0x04, 0x14 };
int nframe = (nbits+7) / 8;
byte *p;
MPI frame;
int i,n,c;
if( (nbits % BITS_PER_MPI_LIMB) || nframe < 42 || len != 20 )
log_bug("can't encode a %d bit MD into a %d bits frame\n",len*8, nbits);
/* We encode the MD in this way:
*
* 0 A PAD(n bytes) 0 ASN(15 bytes) MD(20 bytes)
*
* PAD consists of FF bytes.
*/
frame = mpi_alloc_secure( nframe / BYTES_PER_MPI_LIMB );
n = 0;
for(i=20-1; i >= 0; i--, n++ )
mpi_putbyte(frame, n, md[i] );
for( i=15-1; i >= 0; i--, n++ )
mpi_putbyte(frame, n, asn[i] );
mpi_putbyte(frame, n++, 0 );
while( n < nframe-2 )
mpi_putbyte(frame, n++, 0xff );
mpi_putbyte(frame, n++, DIGEST_ALGO_RMD160 );
mpi_putbyte(frame, n++, 0 );
assert( n == nframe );
return frame;
}
/****************
* Encode a md5 message digest of LEN bytes into NBITS.
* returns: A mpi with the session key (caller must free)
* MD5 Object ID is 1.2.840.113549.2.5
*/
MPI
encode_md5_value( byte *md, unsigned len, unsigned nbits )
{
static byte asn[18] =
{ 0x30, 0x20, 0x30, 0x0c, 0x06, 0x08, 0x2a, 0x86,0x48,
0x86, 0xf7, 0x0d, 0x02, 0x05, 0x05, 0x00, 0x04, 0x10 };
int nframe = (nbits+7) / 8;
byte *p;
MPI frame;
int i,n,c;
if( (nbits % BITS_PER_MPI_LIMB) || nframe < 38 || len != 16 )
log_bug("can't encode a %d bit MD into a %d bits frame\n",len*8, nbits);
/* We encode the MD in this way:
*
* 0 A PAD(n bytes) 0 ASN(18 bytes) MD(16 bytes)
*
* PAD consists of FF bytes.
*/
frame = mpi_alloc_secure( nframe / BYTES_PER_MPI_LIMB );
n = 0;
for(i=16-1; i >= 0; i--, n++ )
mpi_putbyte(frame, n, md[i] );
for( i=18-1; i >= 0; i--, n++ )
mpi_putbyte(frame, n, asn[i] );
mpi_putbyte(frame, n++, 0 );
while( n < nframe-2 )
mpi_putbyte(frame, n++, 0xff );
mpi_putbyte(frame, n++, DIGEST_ALGO_MD5 );
mpi_putbyte(frame, n++, 0 );
assert( n == nframe );
return frame;
}
MPI
encode_md_value( MD_HANDLE md, unsigned nbits )
{
switch( md_get_algo( md ) ) {
case DIGEST_ALGO_MD5:
return encode_md5_value( md_read(md, DIGEST_ALGO_MD5), 16, nbits );
case DIGEST_ALGO_RMD160:
return encode_rmd160_value( md_read(md, DIGEST_ALGO_RMD160), 20, nbits );
case DIGEST_ALGO_SHA1:
return encode_sha1_value( md_read(md, DIGEST_ALGO_SHA1), 20, nbits );
default:
log_bug(NULL);
}
}
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