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Werner Koch
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392
mpi/mpicoder.c
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392
mpi/mpicoder.c
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/* mpicoder.c - Coder for the external representation of MPIs
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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 <assert.h>
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#include "mpi.h"
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#include "iobuf.h"
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#include "memory.h"
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#include "util.h"
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#ifdef M_DEBUG
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#undef mpi_decode
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#undef mpi_decode_buffer
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#endif
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#define MAX_EXTERN_MPI_BITS 16384
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/****************
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* write an mpi to out.
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*/
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int
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mpi_encode( IOBUF out, MPI a )
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{
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u16 dummy;
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return mpi_encode_csum( out, a, &dummy );
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}
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int
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mpi_encode_csum( IOBUF out, MPI a, u16 *csum )
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{
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int i;
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byte c;
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unsigned nbits = a->nlimbs * BITS_PER_MPI_LIMB;
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mpi_limb_t limb;
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#if BYTES_PER_MPI_LIMB != 4
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#error Make this function work with other LIMB sizes
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#endif
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if( nbits > MAX_EXTERN_MPI_BITS )
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log_bug("mpi_encode: mpi too large (%u bits)\n", nbits);
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iobuf_put(out, (c=nbits >>8) ); *csum += c;
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iobuf_put(out, (c=nbits) ); *csum += c;
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for(i=a->nlimbs-1; i >= 0; i-- ) {
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limb = a->d[i];
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iobuf_put(out, (c=limb >> 24) ); *csum += c;
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iobuf_put(out, (c=limb >> 16) ); *csum += c;
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iobuf_put(out, (c=limb >> 8) ); *csum += c;
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iobuf_put(out, (c=limb ) ); *csum += c;
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}
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return 0;
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}
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/****************
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* encode the MPI into a newly allocated buffer, the buffer is
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* so constructed, that it can be used for mpi_write. The caller
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* must free the returned buffer. The buffer is allocated in the same
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* type of memory space as A is.
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*/
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byte *
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mpi_encode_buffer( MPI a )
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{
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abort();
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return NULL;
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}
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/****************
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* write an mpi to out. This is a special function to handle
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* encrypted values. It simply writes the buffer a to OUT.
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* A is a special buffer, starting with 2 bytes giving it's length
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* (in big endian order) and 2 bytes giving it's length in bits (also
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* big endian)
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*/
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int
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mpi_write( IOBUF out, byte *a)
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{
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u16 dummy;
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return mpi_write_csum( out, a, &dummy );
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}
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int
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mpi_write_csum( IOBUF out, byte *a, u16 *csum)
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{
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int rc;
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unsigned n;
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n = *a++ << 8;
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n |= *a++;
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rc = iobuf_write(out, a, n );
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for( ; n; n--, a++ )
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*csum += *a;
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return rc;
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}
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/****************
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* Decode an external representation and return an MPI
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* The external format is a 16 bit unsigned value stored in network byte order,
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* giving the number of bits for the following integer. The integer is stored
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* with MSB first (left padded with zeroes to align on a byte boundary).
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*/
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MPI
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#ifdef M_DEBUG
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mpi_debug_decode(IOBUF inp, unsigned *ret_nread, const char *info)
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#else
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mpi_decode(IOBUF inp, unsigned *ret_nread)
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#endif
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{
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int c, i, j;
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unsigned nbits, nbytes, nlimbs, nread=0;
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mpi_limb_t a;
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MPI val = MPI_NULL;
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if( (c = iobuf_get(inp)) == -1 )
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goto leave;
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nbits = c << 8;
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if( (c = iobuf_get(inp)) == -1 )
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goto leave;
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nbits |= c;
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if( nbits > MAX_EXTERN_MPI_BITS ) {
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log_error("mpi too large (%u bits)\n", nbits);
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goto leave;
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}
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nread = 2;
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nbytes = (nbits+7) / 8;
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nlimbs = (nbytes+BYTES_PER_MPI_LIMB-1) / BYTES_PER_MPI_LIMB;
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#ifdef M_DEBUG
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val = mpi_debug_alloc( nlimbs, info );
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#else
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val = mpi_alloc( nlimbs );
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#endif
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i = BYTES_PER_MPI_LIMB - nbytes % BYTES_PER_MPI_LIMB;
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i %= BYTES_PER_MPI_LIMB;
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j= val->nlimbs = nlimbs;
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val->sign = 0;
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for( ; j > 0; j-- ) {
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a = 0;
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for(; i < BYTES_PER_MPI_LIMB; i++ ) {
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a <<= 8;
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a |= iobuf_get(inp) & 0xff; nread++;
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}
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i = 0;
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val->d[j-1] = a;
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}
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leave:
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if( nread > *ret_nread )
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log_error("Ooops: mpi crosses packet border");
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else
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*ret_nread = nread;
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return val;
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}
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/****************
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* Decode an MPI from the buffer, the buffer starts with two bytes giving
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* the length of the data to follow, the original data follows.
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* The MPI is alloced from secure MPI space
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*/
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MPI
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#ifdef M_DEBUG
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mpi_debug_decode_buffer(byte *buffer, const char *info )
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#else
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mpi_decode_buffer(byte *buffer )
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#endif
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{
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int i, j;
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u16 buflen;
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unsigned nbits, nbytes, nlimbs;
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mpi_limb_t a;
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byte *p = buffer;
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MPI val;
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if( !buffer )
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log_bug("mpi_decode_buffer: no buffer\n");
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buflen = *p++ << 8;
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buflen |= *p++;
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nbits = *p++ << 8;
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nbits |= *p++;
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nbytes = (nbits+7) / 8;
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if( nbytes+2 != buflen )
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log_bug("mpi_decode_buffer: length conflict\n");
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nlimbs = (nbytes+BYTES_PER_MPI_LIMB-1) / BYTES_PER_MPI_LIMB;
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#ifdef M_DEBUG
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val = mpi_debug_alloc_secure( nlimbs, info );
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#else
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val = mpi_alloc_secure( nlimbs );
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#endif
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i = BYTES_PER_MPI_LIMB - nbytes % BYTES_PER_MPI_LIMB;
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i %= BYTES_PER_MPI_LIMB;
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j= val->nlimbs = nlimbs;
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val->sign = 0;
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for( ; j > 0; j-- ) {
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a = 0;
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for(; i < BYTES_PER_MPI_LIMB; i++ ) {
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a <<= 8;
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a |= *p++;
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}
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i = 0;
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val->d[j-1] = a;
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}
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return val;
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}
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/****************
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* Read a MPI from the external medium and return it in a newly allocated
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* buffer (This buffer is allocated in the secure memory space, because
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* we properly need this to decipher this string).
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* Return: the allocated string and in RET_NREAD the number of bytes
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* read (including the 2 length bytes), the returned buffer will
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* be prefixed with two bytes describing the length of the following
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* data.
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*/
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byte *
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mpi_read(IOBUF inp, unsigned *ret_nread)
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{
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int c;
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u16 buflen;
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unsigned nbits, nbytes, nread;
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byte *p, *buf;
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if( (c = iobuf_get(inp)) == -1 )
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return NULL;
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nbits = c << 8;
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if( (c = iobuf_get(inp)) == -1 )
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return NULL;
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nbits |= c;
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if( nbits > MAX_EXTERN_MPI_BITS ) {
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log_error("mpi too large (%u bits)\n", nbits);
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return NULL;
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}
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nread = 2;
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nbytes = (nbits+7) / 8;
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buflen = nbytes + 2;
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p = buf = m_alloc_secure( buflen+2 );
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*p++ = buflen >> 8;
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*p++ = buflen & 0xff;
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*p++ = nbits >> 8;
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*p++ = nbits & 0xff;
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for( ; nbytes ; nbytes--, nread++ )
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*p++ = iobuf_get(inp) & 0xff;
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if( nread > *ret_nread )
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log_error("Ooops: mpi crosses packet border");
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else
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*ret_nread = nread;
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return buf;
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}
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/****************
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* Make a mpi from a character string.
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*/
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int
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mpi_fromstr(MPI val, const char *str)
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{
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int hexmode=0, sign=0, prepend_zero=0, i, j, c, c1, c2;
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unsigned nbits, nbytes, nlimbs;
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mpi_limb_t a;
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if( *str == '-' ) {
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sign = 1;
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str++;
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}
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if( *str == '0' && str[1] == 'x' )
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hexmode = 1;
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else
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return 1; /* other bases are not yet supported */
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str += 2;
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nbits = strlen(str)*4;
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if( nbits % 8 )
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prepend_zero = 1;
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nbytes = (nbits+7) / 8;
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nlimbs = (nbytes+BYTES_PER_MPI_LIMB-1) / BYTES_PER_MPI_LIMB;
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if( val->alloced < nlimbs )
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mpi_resize(val, nlimbs );
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i = BYTES_PER_MPI_LIMB - nbytes % BYTES_PER_MPI_LIMB;
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i %= BYTES_PER_MPI_LIMB;
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j= val->nlimbs = nlimbs;
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val->sign = sign;
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for( ; j > 0; j-- ) {
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a = 0;
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for(; i < BYTES_PER_MPI_LIMB; i++ ) {
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if( prepend_zero ) {
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c1 = '0';
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prepend_zero = 0;
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}
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else
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c1 = *str++;
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assert(c1);
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c2 = *str++;
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assert(c2);
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if( c1 >= '0' && c1 <= '9' )
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c = c1 - '0';
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else if( c1 >= 'a' && c1 <= 'f' )
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c = c1 - 'a' + 10;
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else if( c1 >= 'A' && c1 <= 'F' )
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c = c1 - 'A' + 10;
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else {
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mpi_clear(val);
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return 1;
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}
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c <<= 4;
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if( c2 >= '0' && c2 <= '9' )
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c |= c2 - '0';
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else if( c2 >= 'a' && c2 <= 'f' )
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c |= c2 - 'a' + 10;
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else if( c2 >= 'A' && c2 <= 'F' )
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c |= c2 - 'A' + 10;
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else {
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mpi_clear(val);
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return 1;
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}
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a <<= 8;
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a |= c;
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}
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i = 0;
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val->d[j-1] = a;
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}
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return 0;
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}
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/****************
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* print an MPI to the give stream and return the number of characters
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* printed.
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*/
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int
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mpi_print( FILE *fp, MPI a, int mode )
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{
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int i, n=0;
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if( a == MPI_NULL )
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return fprintf(fp, "[MPI_NULL]");
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if( !mode )
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n += fprintf(fp, "[%d bits]", a->nlimbs * BITS_PER_MPI_LIMB );
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else {
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if( a->sign )
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putc('-', fp);
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for(i=a->nlimbs; i > 0 ; i-- ) {
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n += fprintf(fp, i!=a->nlimbs? "%0" STR2(BYTES_PER_MPI_LIMB2)
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"lX":"%lX", (unsigned long)a->d[i-1] );
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}
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if( !a->nlimbs )
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putc('0', fp );
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}
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return n;
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}
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/****************
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* Special function to get the low 8 bytes from a mpi,
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* this can be used as a keyid, KEYID is an 2 element array.
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* Does return the low 4 bytes.
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*/
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u32
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mpi_get_keyid( MPI a, u32 *keyid )
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{
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#if BYTES_PER_MPI_LIMB != 4
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#error Make this function work with other LIMB sizes
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#endif
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if( keyid ) {
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keyid[0] = a->nlimbs >= 2? a->d[1] : 0;
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keyid[1] = a->nlimbs >= 1? a->d[0] : 0;
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}
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return a->nlimbs >= 1? a->d[0] : 0;
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}
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