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/*
* Gaim-Encryption PSS signature routines, from PKCS#1 v2.1
*
* Copyright (C) 2003 William Tompkins
*
* This program 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.
*
* This program 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 "pk11func.h"
#include "keyhi.h"
/* for g_assert; PORT_Assert seems disabled... */
#include <glib.h>
#include <debug.h>
#include "nss_mgf1.h"
#include "nss_pss.h"
static const SECOidTag Hash_OID = SEC_OID_SHA1;
static const unsigned int hlen = 20; /* SHA1 hash length */
/* Generate a signature block (not including the msg) in the specified space */
/* salt_len is typically = hlen, or 0 */
int pss_generate_sig(unsigned char* sig, unsigned int sig_len,
const unsigned char* msg, unsigned int msg_len, int salt_len) {
/* see PKCS#1 v2.1 for a pretty picture. We construct the signature */
/* left to right, in a very straightforward way. */
/* Since the (variably sized) padding is on the left, we first figure */
/* out where everything is, going right to left. */
unsigned char* bc_pos = sig + sig_len - 1;
unsigned char* final_hash_pos = bc_pos - hlen;
unsigned char* salt_pos = final_hash_pos - salt_len;
int padding2_size = (salt_pos - sig);
unsigned char* m_prime;
SECStatus rv;
/* assuming a modulus size that is a multiple of 8 bits, PS must have at */
/* least one 0 starting off, plus the 1 that denotes the end of PS */
if (padding2_size <= 1) return 0;
/* Construct PS */
PORT_Memset(sig, 0, padding2_size - 1);
sig[padding2_size - 1] = 1;
/* Construct Salt */
rv = PK11_GenerateRandom(salt_pos, salt_len);
g_assert(rv == SECSuccess);
/* Construct M': */
/* If we were clever and had an easy way to incrementally hash things, */
/* we could avoid actually making M' and just use the pieces parts */
/* where they lie. Oh well. */
m_prime = PORT_Alloc(8 + hlen + salt_len);
g_assert(m_prime != 0);
/* Padding1 inside M' */
PORT_Memset(m_prime, 0, 8);
/* mHash inside M' */
rv = PK11_HashBuf(Hash_OID, m_prime + 8, (unsigned char*)msg, msg_len);
g_assert(rv == SECSuccess);
/* salt inside M' */
PORT_Memcpy(m_prime + 8 + hlen, salt_pos, salt_len);
/* Hash M' into final_hash_pos */
rv = PK11_HashBuf(Hash_OID, final_hash_pos, m_prime, 8 + hlen + salt_len);
g_assert(rv == SECSuccess);
PORT_Free(m_prime);
/* Why 0xbc? One of the great mysteries...*/
*bc_pos = 0xbc;
/* Almost done: mask everything before the hash with the hash */
mgf1(sig, final_hash_pos - sig, final_hash_pos, hlen);
/* Mask probably screwed up our starting zero byte, zero it */
sig[0] = 0;
return 1;
}
/* Destructively verify that the the signature block corresponds to */
/* the given message */
int pss_check_sig(unsigned char* sig, unsigned int sig_len,
const unsigned char* msg, unsigned int msg_len) {
unsigned char* bc_pos = sig + sig_len - 1;
unsigned char* final_hash_pos = bc_pos - hlen;
unsigned char* salt_pos;
int salt_len;
unsigned char* m_prime;
unsigned char* check_hash;
int hashcmp;
SECStatus rv;
if (sig[sig_len - 1] != 0xbc) {
gaim_debug(GAIM_DEBUG_ERROR, "gaim-encryption", "No 0xBC in sig\n");
return 0;
}
if (sig[0] != 0) {
gaim_debug(GAIM_DEBUG_ERROR, "gaim-encryption", "First byte of sig nonzero\n");
return 0;
}
mgf1(sig, final_hash_pos - sig, final_hash_pos, hlen);
/* Walk down the padding looking for the 01 that marks the salt */
salt_pos = sig+1;
while ((salt_pos < final_hash_pos) && (*salt_pos == 0)) {
++salt_pos;
}
if (salt_pos == final_hash_pos) {
gaim_debug(GAIM_DEBUG_ERROR, "gaim-encryption", "no 0x01 for salt\n");
return 0;
}
if (*salt_pos != 1) {
gaim_debug(GAIM_DEBUG_ERROR, "gaim-encryption", "no 0x01 for salt (2)\n");
return 0;
}
++salt_pos;
salt_len = final_hash_pos - salt_pos;
/* Construct M' using the salt we just regained */
m_prime = PORT_Alloc(8 + hlen + salt_len);
g_assert(m_prime != 0);
/* Padding1 inside M' */
PORT_Memset(m_prime, 0, 8);
/* mHash inside M' */
rv = PK11_HashBuf(Hash_OID, m_prime + 8, (unsigned char*)msg, msg_len);
g_assert(rv == SECSuccess);
/* salt inside M' */
PORT_Memcpy(m_prime + 8 + hlen, salt_pos, salt_len);
/* Hash M' into check_hash */
check_hash = PORT_Alloc(hlen);
g_assert(m_prime != 0);
rv = PK11_HashBuf(Hash_OID, check_hash, m_prime, 8 + hlen + salt_len);
g_assert(rv == SECSuccess);
PORT_Free(m_prime);
hashcmp = memcmp(check_hash, final_hash_pos, hlen);
PORT_Free(check_hash);
if (hashcmp != 0) {
gaim_debug(GAIM_DEBUG_ERROR, "gaim-encryption", "bad hash in sig\n");
return 0;
}
return 1;
}
void pss_test() {
int mod_size = 512/8;
unsigned char data[4096/8];
unsigned char sig[4096/8];
int data_size;
SECStatus rv;
/* overkill, but what the hey. */
while (mod_size <= 4096/8) {
rv = PK11_GenerateRandom(data, sizeof(data));
g_assert(rv == SECSuccess);
for (data_size = 0; data_size <= 1000; ++data_size) {
g_assert( pss_generate_sig(sig, mod_size, data, data_size, hlen) );
g_assert( pss_check_sig(sig, mod_size, data, data_size) );
g_assert( pss_generate_sig(sig, mod_size, data, data_size, 0) );
g_assert( pss_check_sig(sig, mod_size, data, data_size) );
}
mod_size *= 2;
}
}
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