/*
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* Copyright (C) 2016 The Android Open Source Project
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*
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* Permission is hereby granted, free of charge, to any person
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* obtaining a copy of this software and associated documentation
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* files (the "Software"), to deal in the Software without
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* restriction, including without limitation the rights to use, copy,
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* modify, merge, publish, distribute, sublicense, and/or sell copies
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* of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be
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* included in all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
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* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
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* BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
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* ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
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* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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* SOFTWARE.
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*/
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/* Copyright (c) 2011 The Chromium OS Authors. All rights reserved.
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* Use of this source code is governed by a BSD-style license that can be
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* found in the LICENSE file.
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*/
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/* Implementation of RSA signature verification which uses a pre-processed
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* key for computation. The code extends libmincrypt RSA verification code to
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* support multiple RSA key lengths and hash digest algorithms.
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*/
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#include "avb_rsa.h"
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#include "avb_sha.h"
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#include "avb_util.h"
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#include "avb_vbmeta_image.h"
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typedef struct IAvbKey {
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unsigned int len; /* Length of n[] in number of uint32_t */
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uint32_t n0inv; /* -1 / n[0] mod 2^32 */
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uint32_t* n; /* modulus as array (host-byte order) */
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uint32_t* rr; /* R^2 as array (host-byte order) */
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} IAvbKey;
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static IAvbKey* iavb_parse_key_data(const uint8_t* data, size_t length) {
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AvbRSAPublicKeyHeader h;
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IAvbKey* key = NULL;
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size_t expected_length;
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unsigned int i;
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const uint8_t* n;
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const uint8_t* rr;
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if (!avb_rsa_public_key_header_validate_and_byteswap(
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(const AvbRSAPublicKeyHeader*)data, &h)) {
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avb_error("Invalid key.\n");
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goto fail;
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}
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if (!(h.key_num_bits == 2048 || h.key_num_bits == 4096 ||
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h.key_num_bits == 8192)) {
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avb_error("Unexpected key length.\n");
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goto fail;
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}
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expected_length = sizeof(AvbRSAPublicKeyHeader) + 2 * h.key_num_bits / 8;
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if (length != expected_length) {
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avb_error("Key does not match expected length.\n");
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goto fail;
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}
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n = data + sizeof(AvbRSAPublicKeyHeader);
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rr = data + sizeof(AvbRSAPublicKeyHeader) + h.key_num_bits / 8;
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/* Store n and rr following the key header so we only have to do one
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* allocation.
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*/
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key = (IAvbKey*)(avb_malloc(sizeof(IAvbKey) + 2 * h.key_num_bits / 8));
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if (key == NULL) {
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goto fail;
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}
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key->len = h.key_num_bits / 32;
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key->n0inv = h.n0inv;
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key->n = (uint32_t*)(key + 1); /* Skip ahead sizeof(IAvbKey) bytes. */
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key->rr = key->n + key->len;
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/* Crypto-code below (modpowF4() and friends) expects the key in
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* little-endian format (rather than the format we're storing the
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* key in), so convert it.
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*/
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for (i = 0; i < key->len; i++) {
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key->n[i] = avb_be32toh(((uint32_t*)n)[key->len - i - 1]);
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key->rr[i] = avb_be32toh(((uint32_t*)rr)[key->len - i - 1]);
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}
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return key;
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fail:
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if (key != NULL) {
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avb_free(key);
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}
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return NULL;
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}
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static void iavb_free_parsed_key(IAvbKey* key) {
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avb_free(key);
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}
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/* a[] -= mod */
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static void subM(const IAvbKey* key, uint32_t* a) {
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int64_t A = 0;
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uint32_t i;
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for (i = 0; i < key->len; ++i) {
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A += (uint64_t)a[i] - key->n[i];
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a[i] = (uint32_t)A;
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A >>= 32;
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}
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}
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/* return a[] >= mod */
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static int geM(const IAvbKey* key, uint32_t* a) {
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uint32_t i;
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for (i = key->len; i;) {
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--i;
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if (a[i] < key->n[i]) {
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return 0;
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}
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if (a[i] > key->n[i]) {
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return 1;
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}
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}
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return 1; /* equal */
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}
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/* montgomery c[] += a * b[] / R % mod */
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static void montMulAdd(const IAvbKey* key,
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uint32_t* c,
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const uint32_t a,
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const uint32_t* b) {
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uint64_t A = (uint64_t)a * b[0] + c[0];
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uint32_t d0 = (uint32_t)A * key->n0inv;
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uint64_t B = (uint64_t)d0 * key->n[0] + (uint32_t)A;
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uint32_t i;
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for (i = 1; i < key->len; ++i) {
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A = (A >> 32) + (uint64_t)a * b[i] + c[i];
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B = (B >> 32) + (uint64_t)d0 * key->n[i] + (uint32_t)A;
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c[i - 1] = (uint32_t)B;
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}
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A = (A >> 32) + (B >> 32);
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c[i - 1] = (uint32_t)A;
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if (A >> 32) {
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subM(key, c);
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}
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}
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/* montgomery c[] = a[] * b[] / R % mod */
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static void montMul(const IAvbKey* key, uint32_t* c, uint32_t* a, uint32_t* b) {
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uint32_t i;
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for (i = 0; i < key->len; ++i) {
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c[i] = 0;
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}
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for (i = 0; i < key->len; ++i) {
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montMulAdd(key, c, a[i], b);
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}
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}
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/* In-place public exponentiation. (65537}
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* Input and output big-endian byte array in inout.
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*/
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static void modpowF4(const IAvbKey* key, uint8_t* inout) {
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uint32_t* a = (uint32_t*)avb_malloc(key->len * sizeof(uint32_t));
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uint32_t* aR = (uint32_t*)avb_malloc(key->len * sizeof(uint32_t));
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uint32_t* aaR = (uint32_t*)avb_malloc(key->len * sizeof(uint32_t));
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if (a == NULL || aR == NULL || aaR == NULL) {
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goto out;
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}
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uint32_t* aaa = aaR; /* Re-use location. */
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int i;
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/* Convert from big endian byte array to little endian word array. */
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for (i = 0; i < (int)key->len; ++i) {
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uint32_t tmp = (inout[((key->len - 1 - i) * 4) + 0] << 24) |
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(inout[((key->len - 1 - i) * 4) + 1] << 16) |
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(inout[((key->len - 1 - i) * 4) + 2] << 8) |
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(inout[((key->len - 1 - i) * 4) + 3] << 0);
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a[i] = tmp;
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}
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montMul(key, aR, a, key->rr); /* aR = a * RR / R mod M */
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for (i = 0; i < 16; i += 2) {
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montMul(key, aaR, aR, aR); /* aaR = aR * aR / R mod M */
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montMul(key, aR, aaR, aaR); /* aR = aaR * aaR / R mod M */
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}
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montMul(key, aaa, aR, a); /* aaa = aR * a / R mod M */
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/* Make sure aaa < mod; aaa is at most 1x mod too large. */
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if (geM(key, aaa)) {
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subM(key, aaa);
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}
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/* Convert to bigendian byte array */
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for (i = (int)key->len - 1; i >= 0; --i) {
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uint32_t tmp = aaa[i];
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*inout++ = (uint8_t)(tmp >> 24);
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*inout++ = (uint8_t)(tmp >> 16);
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*inout++ = (uint8_t)(tmp >> 8);
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*inout++ = (uint8_t)(tmp >> 0);
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}
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out:
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if (a != NULL) {
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avb_free(a);
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}
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if (aR != NULL) {
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avb_free(aR);
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}
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if (aaR != NULL) {
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avb_free(aaR);
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}
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}
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/* Verify a RSA PKCS1.5 signature against an expected hash.
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* Returns false on failure, true on success.
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*/
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bool avb_rsa_verify(const uint8_t* key,
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size_t key_num_bytes,
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const uint8_t* sig,
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size_t sig_num_bytes,
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const uint8_t* hash,
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size_t hash_num_bytes,
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const uint8_t* padding,
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size_t padding_num_bytes) {
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uint8_t* buf = NULL;
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IAvbKey* parsed_key = NULL;
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bool success = false;
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if (key == NULL || sig == NULL || hash == NULL || padding == NULL) {
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avb_error("Invalid input.\n");
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goto out;
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}
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parsed_key = iavb_parse_key_data(key, key_num_bytes);
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if (parsed_key == NULL) {
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avb_error("Error parsing key.\n");
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goto out;
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}
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if (sig_num_bytes != (parsed_key->len * sizeof(uint32_t))) {
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avb_error("Signature length does not match key length.\n");
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goto out;
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}
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if (padding_num_bytes != sig_num_bytes - hash_num_bytes) {
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avb_error("Padding length does not match hash and signature lengths.\n");
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goto out;
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}
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buf = (uint8_t*)avb_malloc(sig_num_bytes);
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if (buf == NULL) {
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avb_error("Error allocating memory.\n");
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goto out;
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}
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avb_memcpy(buf, sig, sig_num_bytes);
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modpowF4(parsed_key, buf);
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/* Check padding bytes.
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*
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* Even though there are probably no timing issues here, we use
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* avb_safe_memcmp() just to be on the safe side.
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*/
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if (avb_safe_memcmp(buf, padding, padding_num_bytes)) {
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avb_error("Padding check failed.\n");
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goto out;
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}
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/* Check hash. */
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if (avb_safe_memcmp(buf + padding_num_bytes, hash, hash_num_bytes)) {
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avb_error("Hash check failed.\n");
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goto out;
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}
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success = true;
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out:
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if (parsed_key != NULL) {
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iavb_free_parsed_key(parsed_key);
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}
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if (buf != NULL) {
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avb_free(buf);
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}
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return success;
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}
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