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240 lines
6.8 KiB
C
240 lines
6.8 KiB
C
/* seskey.c - make sesssion keys etc.
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* Copyright (c) 1997 by Werner Koch (dd9jn)
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*
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* This file is part of G10.
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*
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* G10 is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* G10 is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
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*/
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#include <config.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <assert.h>
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#include "util.h"
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#include "cipher.h"
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#include "mpi.h"
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#include "main.h"
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/****************
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* Make a session key and put it into DEK
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*/
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void
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make_session_key( DEK *dek )
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{
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switch( dek->algo ) {
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case CIPHER_ALGO_BLOWFISH:
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dek->keylen = 20;
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randomize_buffer( dek->key, dek->keylen, 1 );
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break;
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case CIPHER_ALGO_BLOWFISH128:
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dek->keylen = 16;
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randomize_buffer( dek->key, dek->keylen, 1 );
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break;
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default: log_bug("invalid algo %d in make_session_key()\n", dek->algo);
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}
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}
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/****************
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* Encode the session key. NBITS is the number of bits which should be used
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* for packing the session key.
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* returns: A mpi with the session key (caller must free)
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*/
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MPI
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encode_session_key( DEK *dek, unsigned nbits )
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{
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int nframe = (nbits+7) / 8;
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byte *p;
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MPI frame;
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int i,n,c;
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u16 csum;
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/* the current limitation is, that we can only use a session key
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* which length is a multiple of BITS_PER_MPI_LIMB
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* I think we can live with that.
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*/
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if( dek->keylen + 7 > nframe || (nbits % BITS_PER_MPI_LIMB) || !nframe )
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log_bug("can't encode a %d bit key in a %d bits frame\n",
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dek->keylen*8, nbits );
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/* We encode the session key in this way:
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*
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* 0 2 RND(n bytes) 0 A DEK(k bytes) CSUM(2 bytes)
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*
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* RND are non-zero random bytes.
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* A is the cipher algorithm
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* DEK is the encryption key (session key) length k depends on the
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* cipher algorithm (20 is used with blowfish).
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* CSUM is the 16 bit checksum over the DEK
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*/
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frame = mpi_alloc_secure( nframe / BYTES_PER_MPI_LIMB );
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csum = 0;
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for( p = dek->key, i=0; i < dek->keylen; i++ )
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csum += *p++;
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mpi_putbyte(frame, 0, csum );
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mpi_putbyte(frame, 1, csum >> 8 );
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for(n=2,i=dek->keylen-1, p = dek->key; i >= 0; i--, n++ )
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mpi_putbyte(frame, n, p[i] );
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mpi_putbyte(frame, n++, dek->algo );
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mpi_putbyte(frame, n++, 0 );
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while( n < nframe-2 ) {
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while( !(c = get_random_byte(1)) )
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;
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mpi_putbyte(frame, n++, c );
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}
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mpi_putbyte(frame, n++, 2 );
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mpi_putbyte(frame, n++, 0 );
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assert( n == nframe );
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return frame;
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}
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/****************
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* Encode a ripemd160 message digest of LEN bytes into NBITS.
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* returns: A mpi with the session key (caller must free)
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* RMD160 Object ID is 1.3.36.3.2.1
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*/
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MPI
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encode_rmd160_value( byte *md, unsigned len, unsigned nbits )
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{
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static byte asn[15] =
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{ 0x30, 0x21, 0x30, 0x09, 0x06, 0x05, 0x2b, 0x24, 0x03,
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0x02, 0x01, 0x05, 0x00, 0x04, 0x14 };
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int nframe = (nbits+7) / 8;
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MPI frame;
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int i,n;
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if( (nbits % BITS_PER_MPI_LIMB) || nframe < 42 || len != 20 )
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log_bug("can't encode a %d bit MD into a %d bits frame\n",len*8, nbits);
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/* We encode the MD in this way:
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*
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* 0 A PAD(n bytes) 0 ASN(15 bytes) MD(20 bytes)
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*
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* PAD consists of FF bytes.
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*/
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frame = mpi_alloc_secure( nframe / BYTES_PER_MPI_LIMB );
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n = 0;
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for(i=20-1; i >= 0; i--, n++ )
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mpi_putbyte(frame, n, md[i] );
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for( i=15-1; i >= 0; i--, n++ )
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mpi_putbyte(frame, n, asn[i] );
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mpi_putbyte(frame, n++, 0 );
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while( n < nframe-2 )
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mpi_putbyte(frame, n++, 0xff );
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mpi_putbyte(frame, n++, DIGEST_ALGO_RMD160 );
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mpi_putbyte(frame, n++, 0 );
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assert( n == nframe );
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return frame;
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}
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/****************
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* Encode a sha-1 message digest of LEN bytes into NBITS.
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* returns: A mpi with the session key (caller must free)
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* SHA-1 Objet ID is 1.3.14.3.2.26
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*/
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MPI
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encode_sha1_value( byte *md, unsigned len, unsigned nbits )
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{
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static byte asn[15] =
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{ 0x30, 0x21, 0x30, 0x09, 0x06, 0x05, 0x2b, 0x0e, 0x03,
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0x02, 0x1a, 0x05, 0x00, 0x04, 0x14 };
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int nframe = (nbits+7) / 8;
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MPI frame;
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int i,n;
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if( (nbits % BITS_PER_MPI_LIMB) || nframe < 42 || len != 20 )
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log_bug("can't encode a %d bit MD into a %d bits frame\n",len*8, nbits);
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/* We encode the MD in this way:
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*
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* 0 A PAD(n bytes) 0 ASN(15 bytes) MD(20 bytes)
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*
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* PAD consists of FF bytes.
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*/
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frame = mpi_alloc_secure( nframe / BYTES_PER_MPI_LIMB );
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n = 0;
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for(i=20-1; i >= 0; i--, n++ )
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mpi_putbyte(frame, n, md[i] );
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for( i=15-1; i >= 0; i--, n++ )
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mpi_putbyte(frame, n, asn[i] );
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mpi_putbyte(frame, n++, 0 );
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while( n < nframe-2 )
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mpi_putbyte(frame, n++, 0xff );
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mpi_putbyte(frame, n++, DIGEST_ALGO_RMD160 );
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mpi_putbyte(frame, n++, 0 );
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assert( n == nframe );
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return frame;
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}
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/****************
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* Encode a md5 message digest of LEN bytes into NBITS.
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* returns: A mpi with the session key (caller must free)
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* MD5 Object ID is 1.2.840.113549.2.5
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*/
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MPI
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encode_md5_value( byte *md, unsigned len, unsigned nbits )
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{
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static byte asn[18] =
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{ 0x30, 0x20, 0x30, 0x0c, 0x06, 0x08, 0x2a, 0x86,0x48,
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0x86, 0xf7, 0x0d, 0x02, 0x05, 0x05, 0x00, 0x04, 0x10 };
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int nframe = (nbits+7) / 8;
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MPI frame;
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int i,n;
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if( (nbits % BITS_PER_MPI_LIMB) || nframe < 38 || len != 16 )
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log_bug("can't encode a %d bit MD into a %d bits frame\n",len*8, nbits);
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/* We encode the MD in this way:
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*
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* 0 A PAD(n bytes) 0 ASN(18 bytes) MD(16 bytes)
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*
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* PAD consists of FF bytes.
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*/
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frame = mpi_alloc_secure( nframe / BYTES_PER_MPI_LIMB );
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n = 0;
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for(i=16-1; i >= 0; i--, n++ )
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mpi_putbyte(frame, n, md[i] );
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for( i=18-1; i >= 0; i--, n++ )
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mpi_putbyte(frame, n, asn[i] );
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mpi_putbyte(frame, n++, 0 );
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while( n < nframe-2 )
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mpi_putbyte(frame, n++, 0xff );
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mpi_putbyte(frame, n++, DIGEST_ALGO_MD5 );
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mpi_putbyte(frame, n++, 0 );
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assert( n == nframe );
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return frame;
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}
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MPI
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encode_md_value( MD_HANDLE md, unsigned nbits )
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{
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switch( md_get_algo( md ) ) {
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case DIGEST_ALGO_MD5:
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return encode_md5_value( md_read(md, DIGEST_ALGO_MD5), 16, nbits );
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case DIGEST_ALGO_RMD160:
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return encode_rmd160_value( md_read(md, DIGEST_ALGO_RMD160), 20, nbits );
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case DIGEST_ALGO_SHA1:
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return encode_sha1_value( md_read(md, DIGEST_ALGO_SHA1), 20, nbits );
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default:
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BUG();
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}
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}
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