/* 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 #include #include #include #include #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; 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 ) { byte *p = md_final( md ); if( md->algo == DIGEST_ALGO_MD5 ) return encode_md5_value( p, 16, nbits ); else if( md->algo == DIGEST_ALGO_RMD160 ) return encode_rmd160_value( p, 20, nbits ); else if( md->algo == DIGEST_ALGO_SHA1 ) return encode_sha1_value( p, 20, nbits ); else log_bug(NULL); }