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- // 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"
- #include <malloc.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;
- }
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