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/* Copyright (c) 2011 The Chromium OS Authors. All rights reserved.
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
*/
/* Implementation of RSA signature verification which uses a pre-processed
* key for computation. The code extends Android's RSA verification code to
* support multiple RSA key lengths and hash digest algorithms.
*/
#include "sysincludes.h"
#include "cryptolib.h"
#include "vboot_api.h"
#include "utility.h"
/* a[] -= mod */
static void subM(const RSAPublicKey *key, uint32_t *a) {
int64_t A = 0;
uint32_t i;
for (i = 0; i < key->len; ++i) {
A += (uint64_t)a[i] - key->n[i];
a[i] = (uint32_t)A;
A >>= 32;
}
}
/* return a[] >= mod */
static int geM(const RSAPublicKey *key, uint32_t *a) {
uint32_t i;
for (i = key->len; i;) {
--i;
if (a[i] < key->n[i]) return 0;
if (a[i] > key->n[i]) return 1;
}
return 1; /* equal */
}
/* montgomery c[] += a * b[] / R % mod */
static void montMulAdd(const RSAPublicKey *key,
uint32_t* c,
const uint32_t a,
const uint32_t* b) {
uint64_t A = (uint64_t)a * b[0] + c[0];
uint32_t d0 = (uint32_t)A * key->n0inv;
uint64_t B = (uint64_t)d0 * key->n[0] + (uint32_t)A;
uint32_t i;
for (i = 1; i < key->len; ++i) {
A = (A >> 32) + (uint64_t)a * b[i] + c[i];
B = (B >> 32) + (uint64_t)d0 * key->n[i] + (uint32_t)A;
c[i - 1] = (uint32_t)B;
}
A = (A >> 32) + (B >> 32);
c[i - 1] = (uint32_t)A;
if (A >> 32) {
subM(key, c);
}
}
/* montgomery c[] = a[] * b[] / R % mod */
static void montMul(const RSAPublicKey *key,
uint32_t* c,
uint32_t* a,
uint32_t* b) {
uint32_t i;
for (i = 0; i < key->len; ++i) {
c[i] = 0;
}
for (i = 0; i < key->len; ++i) {
montMulAdd(key, c, a[i], b);
}
}
/* In-place public exponentiation. (65537}
* Input and output big-endian byte array in inout.
*/
static void modpowF4(const RSAPublicKey *key,
uint8_t* inout) {
uint32_t* a = (uint32_t*) VbExMalloc(key->len * sizeof(uint32_t));
uint32_t* aR = (uint32_t*) VbExMalloc(key->len * sizeof(uint32_t));
uint32_t* aaR = (uint32_t*) VbExMalloc(key->len * sizeof(uint32_t));
uint32_t* aaa = aaR; /* Re-use location. */
int i;
/* Convert from big endian byte array to little endian word array. */
for (i = 0; i < (int)key->len; ++i) {
uint32_t tmp =
(inout[((key->len - 1 - i) * 4) + 0] << 24) |
(inout[((key->len - 1 - i) * 4) + 1] << 16) |
(inout[((key->len - 1 - i) * 4) + 2] << 8) |
(inout[((key->len - 1 - i) * 4) + 3] << 0);
a[i] = tmp;
}
montMul(key, aR, a, key->rr); /* aR = a * RR / R mod M */
for (i = 0; i < 16; i+=2) {
montMul(key, aaR, aR, aR); /* aaR = aR * aR / R mod M */
montMul(key, aR, aaR, aaR); /* aR = aaR * aaR / R mod M */
}
montMul(key, aaa, aR, a); /* aaa = aR * a / R mod M */
/* Make sure aaa < mod; aaa is at most 1x mod too large. */
if (geM(key, aaa)) {
subM(key, aaa);
}
/* Convert to bigendian byte array */
for (i = (int)key->len - 1; i >= 0; --i) {
uint32_t tmp = aaa[i];
*inout++ = (uint8_t)(tmp >> 24);
*inout++ = (uint8_t)(tmp >> 16);
*inout++ = (uint8_t)(tmp >> 8);
*inout++ = (uint8_t)(tmp >> 0);
}
VbExFree(a);
VbExFree(aR);
VbExFree(aaR);
}
/* Verify a RSA PKCS1.5 signature against an expected hash.
* Returns 0 on failure, 1 on success.
*/
int RSAVerify(const RSAPublicKey *key,
const uint8_t *sig,
const uint32_t sig_len,
const uint8_t sig_type,
const uint8_t *hash) {
uint8_t* buf;
const uint8_t* padding;
int padding_len;
int success = 1;
if (!key || !sig || !hash)
return 0;
if (sig_len != (key->len * sizeof(uint32_t))) {
VBDEBUG(("Signature is of incorrect length!\n"));
return 0;
}
if (sig_type >= kNumAlgorithms) {
VBDEBUG(("Invalid signature type!\n"));
return 0;
}
if (key->len != siglen_map[sig_type] / sizeof(uint32_t)) {
VBDEBUG(("Wrong key passed in!\n"));
return 0;
}
buf = (uint8_t*) VbExMalloc(sig_len);
if (!buf)
return 0;
Memcpy(buf, sig, sig_len);
modpowF4(key, buf);
/* Determine padding to use depending on the signature type. */
padding = padding_map[sig_type];
padding_len = padding_size_map[sig_type];
/* Even though there are probably no timing issues here, we use
* SafeMemcmp() just to be on the safe side. */
/* Check pkcs1.5 padding bytes. */
if (SafeMemcmp(buf, padding, padding_len)) {
VBDEBUG(("In RSAVerify(): Padding check failed!\n"));
success = 0;
}
/* Check hash. */
if (SafeMemcmp(buf + padding_len, hash, sig_len - padding_len)) {
VBDEBUG(("In RSAVerify(): Hash check failed!\n"));
success = 0;
}
VbExFree(buf);
return success;
}
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