276 lines
7.1 KiB
C
276 lines
7.1 KiB
C
// SPDX-License-Identifier: MIT OR BSD-3-Clause
|
|
/*
|
|
* Copyright (C) 2016 The Android Open Source Project
|
|
*/
|
|
|
|
/* Implementation of RSA signature verification which uses a pre-processed
|
|
* key for computation. The code extends libmincrypt RSA verification code to
|
|
* support multiple RSA key lengths and hash digest algorithms.
|
|
*/
|
|
|
|
#include "avb_rsa.h"
|
|
#include "avb_sha.h"
|
|
#include "avb_util.h"
|
|
#include "avb_vbmeta_image.h"
|
|
|
|
typedef struct IAvbKey {
|
|
unsigned int len; /* Length of n[] in number of uint32_t */
|
|
uint32_t n0inv; /* -1 / n[0] mod 2^32 */
|
|
uint32_t* n; /* modulus as array (host-byte order) */
|
|
uint32_t* rr; /* R^2 as array (host-byte order) */
|
|
} IAvbKey;
|
|
|
|
static IAvbKey* iavb_parse_key_data(const uint8_t* data, size_t length) {
|
|
AvbRSAPublicKeyHeader h;
|
|
IAvbKey* key = NULL;
|
|
size_t expected_length;
|
|
unsigned int i;
|
|
const uint8_t* n;
|
|
const uint8_t* rr;
|
|
|
|
if (!avb_rsa_public_key_header_validate_and_byteswap(
|
|
(const AvbRSAPublicKeyHeader*)data, &h)) {
|
|
avb_error("Invalid key.\n");
|
|
goto fail;
|
|
}
|
|
|
|
if (!(h.key_num_bits == 2048 || h.key_num_bits == 4096 ||
|
|
h.key_num_bits == 8192)) {
|
|
avb_error("Unexpected key length.\n");
|
|
goto fail;
|
|
}
|
|
|
|
expected_length = sizeof(AvbRSAPublicKeyHeader) + 2 * h.key_num_bits / 8;
|
|
if (length != expected_length) {
|
|
avb_error("Key does not match expected length.\n");
|
|
goto fail;
|
|
}
|
|
|
|
n = data + sizeof(AvbRSAPublicKeyHeader);
|
|
rr = data + sizeof(AvbRSAPublicKeyHeader) + h.key_num_bits / 8;
|
|
|
|
/* Store n and rr following the key header so we only have to do one
|
|
* allocation.
|
|
*/
|
|
key = (IAvbKey*)(avb_malloc(sizeof(IAvbKey) + 2 * h.key_num_bits / 8));
|
|
if (key == NULL) {
|
|
goto fail;
|
|
}
|
|
|
|
key->len = h.key_num_bits / 32;
|
|
key->n0inv = h.n0inv;
|
|
key->n = (uint32_t*)(key + 1); /* Skip ahead sizeof(IAvbKey) bytes. */
|
|
key->rr = key->n + key->len;
|
|
|
|
/* Crypto-code below (modpowF4() and friends) expects the key in
|
|
* little-endian format (rather than the format we're storing the
|
|
* key in), so convert it.
|
|
*/
|
|
for (i = 0; i < key->len; i++) {
|
|
key->n[i] = avb_be32toh(((uint32_t*)n)[key->len - i - 1]);
|
|
key->rr[i] = avb_be32toh(((uint32_t*)rr)[key->len - i - 1]);
|
|
}
|
|
return key;
|
|
|
|
fail:
|
|
if (key != NULL) {
|
|
avb_free(key);
|
|
}
|
|
return NULL;
|
|
}
|
|
|
|
static void iavb_free_parsed_key(IAvbKey* key) {
|
|
avb_free(key);
|
|
}
|
|
|
|
/* a[] -= mod */
|
|
static void subM(const IAvbKey* 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 IAvbKey* 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 IAvbKey* 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 IAvbKey* 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 IAvbKey* key, uint8_t* inout) {
|
|
uint32_t* a = (uint32_t*)avb_malloc(key->len * sizeof(uint32_t));
|
|
uint32_t* aR = (uint32_t*)avb_malloc(key->len * sizeof(uint32_t));
|
|
uint32_t* aaR = (uint32_t*)avb_malloc(key->len * sizeof(uint32_t));
|
|
if (a == NULL || aR == NULL || aaR == NULL) {
|
|
goto out;
|
|
}
|
|
|
|
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);
|
|
}
|
|
|
|
out:
|
|
if (a != NULL) {
|
|
avb_free(a);
|
|
}
|
|
if (aR != NULL) {
|
|
avb_free(aR);
|
|
}
|
|
if (aaR != NULL) {
|
|
avb_free(aaR);
|
|
}
|
|
}
|
|
|
|
/* Verify a RSA PKCS1.5 signature against an expected hash.
|
|
* Returns false on failure, true on success.
|
|
*/
|
|
bool avb_rsa_verify(const uint8_t* key,
|
|
size_t key_num_bytes,
|
|
const uint8_t* sig,
|
|
size_t sig_num_bytes,
|
|
const uint8_t* hash,
|
|
size_t hash_num_bytes,
|
|
const uint8_t* padding,
|
|
size_t padding_num_bytes) {
|
|
uint8_t* buf = NULL;
|
|
IAvbKey* parsed_key = NULL;
|
|
bool success = false;
|
|
|
|
if (key == NULL || sig == NULL || hash == NULL || padding == NULL) {
|
|
avb_error("Invalid input.\n");
|
|
goto out;
|
|
}
|
|
|
|
parsed_key = iavb_parse_key_data(key, key_num_bytes);
|
|
if (parsed_key == NULL) {
|
|
avb_error("Error parsing key.\n");
|
|
goto out;
|
|
}
|
|
|
|
if (sig_num_bytes != (parsed_key->len * sizeof(uint32_t))) {
|
|
avb_error("Signature length does not match key length.\n");
|
|
goto out;
|
|
}
|
|
|
|
if (padding_num_bytes != sig_num_bytes - hash_num_bytes) {
|
|
avb_error("Padding length does not match hash and signature lengths.\n");
|
|
goto out;
|
|
}
|
|
|
|
buf = (uint8_t*)avb_malloc(sig_num_bytes);
|
|
if (buf == NULL) {
|
|
avb_error("Error allocating memory.\n");
|
|
goto out;
|
|
}
|
|
avb_memcpy(buf, sig, sig_num_bytes);
|
|
|
|
modpowF4(parsed_key, buf);
|
|
|
|
/* Check padding bytes.
|
|
*
|
|
* Even though there are probably no timing issues here, we use
|
|
* avb_safe_memcmp() just to be on the safe side.
|
|
*/
|
|
if (avb_safe_memcmp(buf, padding, padding_num_bytes)) {
|
|
avb_error("Padding check failed.\n");
|
|
goto out;
|
|
}
|
|
|
|
/* Check hash. */
|
|
if (avb_safe_memcmp(buf + padding_num_bytes, hash, hash_num_bytes)) {
|
|
avb_error("Hash check failed.\n");
|
|
goto out;
|
|
}
|
|
|
|
success = true;
|
|
|
|
out:
|
|
if (parsed_key != NULL) {
|
|
iavb_free_parsed_key(parsed_key);
|
|
}
|
|
if (buf != NULL) {
|
|
avb_free(buf);
|
|
}
|
|
return success;
|
|
}
|