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/* pkcs1.c
*
* PKCS1 embedding.
*/
/* nettle, low-level cryptographics library
*
* Copyright (C) 2003 Niels Möller
*
* The nettle library is free software; you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as published by
* the Free Software Foundation; either version 2.1 of the License, or (at your
* option) any later version.
*
* The nettle library 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 Lesser General Public
* License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with the nettle library; see the file COPYING.LIB. If not, write to
* the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
* MA 02111-1301, USA.
*/
#if HAVE_CONFIG_H
# include "config.h"
#endif
#include <assert.h>
#include <string.h>
#include "pkcs1.h"
/* Formats the PKCS#1 padding, of the form
*
* 0x00 0x01 0xff ... 0xff 0x00 id ...digest...
*
* where the 0xff ... 0xff part consists of at least 8 octets. The
* total size equals the octet size of n.
*/
uint8_t *
_pkcs1_signature_prefix(unsigned key_size,
uint8_t *buffer,
unsigned id_size,
const uint8_t *id,
unsigned digest_size)
{
unsigned j;
if (key_size < 11 + id_size + digest_size)
return NULL;
j = key_size - digest_size - id_size;
memcpy (buffer + j, id, id_size);
buffer[0] = 0;
buffer[1] = 1;
buffer[j-1] = 0;
assert(j >= 11);
memset(buffer + 2, 0xff, j - 3);
return buffer + j + id_size;
}
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