mincrypt: merge the two RSA verifiers
The e=3 and e=65537 implementations are nearly identical, refactor
them down into one.
Change-Id: I537a368a6cc195f373b9354d7472957fd683beea
diff --git a/libmincrypt/rsa.c b/libmincrypt/rsa.c
index 0cdbaa2..9061b3a 100644
--- a/libmincrypt/rsa.c
+++ b/libmincrypt/rsa.c
@@ -26,32 +26,283 @@
*/
#include "mincrypt/rsa.h"
+#include "mincrypt/sha.h"
+#include "mincrypt/sha256.h"
-int RSA_e_f4_verify(const RSAPublicKey* key,
- const uint8_t* signature,
- const int len,
- const uint8_t* hash,
- const int hash_len);
+// a[] -= mod
+static void subM(const RSAPublicKey* key,
+ uint32_t* a) {
+ int64_t A = 0;
+ int i;
+ for (i = 0; i < key->len; ++i) {
+ A += (uint64_t)a[i] - key->n[i];
+ a[i] = (uint32_t)A;
+ A >>= 32;
+ }
+}
-int RSA_e_3_verify(const RSAPublicKey *key,
- const uint8_t *signature,
- const int len,
- const uint8_t *hash,
- const int hash_len);
+// return a[] >= mod
+static int geM(const RSAPublicKey* key,
+ const uint32_t* a) {
+ int 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;
+ int 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,
+ const uint32_t* a,
+ const uint32_t* b) {
+ int 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.
+// Input and output big-endian byte array in inout.
+static void modpow(const RSAPublicKey* key,
+ uint8_t* inout) {
+ uint32_t a[RSANUMWORDS];
+ uint32_t aR[RSANUMWORDS];
+ uint32_t aaR[RSANUMWORDS];
+ uint32_t* aaa = 0;
+ int i;
+
+ // Convert from big endian byte array to little endian word array.
+ for (i = 0; i < 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;
+ }
+
+ if (key->exponent == 65537) {
+ aaa = aaR; // Re-use location.
+ 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
+ } else if (key->exponent == 3) {
+ aaa = aR; // Re-use location.
+ montMul(key, aR, a, key->rr); /* aR = a * RR / R mod M */
+ montMul(key, aaR, aR, aR); /* aaR = aR * aR / R mod M */
+ montMul(key, aaa, aaR, a); /* aaa = aaR * 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 = key->len - 1; i >= 0; --i) {
+ uint32_t tmp = aaa[i];
+ *inout++ = tmp >> 24;
+ *inout++ = tmp >> 16;
+ *inout++ = tmp >> 8;
+ *inout++ = tmp >> 0;
+ }
+}
+
+// Expected PKCS1.5 signature padding bytes, for a keytool RSA signature.
+// Has the 0-length optional parameter encoded in the ASN1 (as opposed to the
+// other flavor which omits the optional parameter entirely). This code does not
+// accept signatures without the optional parameter.
+
+/*
+static const uint8_t sha_padding[RSANUMBYTES] = {
+ 0x00, 0x01, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0x00, 0x30, 0x21, 0x30,
+ 0x09, 0x06, 0x05, 0x2b, 0x0e, 0x03, 0x02, 0x1a,
+ 0x05, 0x00, 0x04, 0x14,
+
+ // 20 bytes of hash go here.
+ 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
+};
+*/
+
+// SHA-1 of PKCS1.5 signature sha_padding for 2048 bit, as above.
+// At the location of the bytes of the hash all 00 are hashed.
+static const uint8_t kExpectedPadShaRsa2048[SHA_DIGEST_SIZE] = {
+ 0xdc, 0xbd, 0xbe, 0x42, 0xd5, 0xf5, 0xa7, 0x2e,
+ 0x6e, 0xfc, 0xf5, 0x5d, 0xaf, 0x9d, 0xea, 0x68,
+ 0x7c, 0xfb, 0xf1, 0x67
+};
+
+/*
+static const uint8_t sha256_padding[RSANUMBYTES] = {
+ 0x00, 0x01, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0x00, 0x30, 0x31, 0x30,
+ 0x0d, 0x06, 0x09, 0x60, 0x86, 0x48, 0x01, 0x65,
+ 0x03, 0x04, 0x02, 0x01, 0x05, 0x00, 0x04, 0x20,
+
+ // 32 bytes of hash go here.
+ 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
+ 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
+};
+*/
+
+// SHA-256 of PKCS1.5 signature sha256_padding for 2048 bit, as above.
+// At the location of the bytes of the hash all 00 are hashed.
+static const uint8_t kExpectedPadSha256Rsa2048[SHA256_DIGEST_SIZE] = {
+ 0xab, 0x28, 0x8d, 0x8a, 0xd7, 0xd9, 0x59, 0x92,
+ 0xba, 0xcc, 0xf8, 0x67, 0x20, 0xe1, 0x15, 0x2e,
+ 0x39, 0x8d, 0x80, 0x36, 0xd6, 0x6f, 0xf0, 0xfd,
+ 0x90, 0xe8, 0x7d, 0x8b, 0xe1, 0x7c, 0x87, 0x59,
+};
+
+// Verify a 2048-bit RSA PKCS1.5 signature against an expected hash.
+// Both e=3 and e=65537 are supported. hash_len may be
+// SHA_DIGEST_SIZE (== 20) to indicate a SHA-1 hash, or
+// SHA256_DIGEST_SIZE (== 32) to indicate a SHA-256 hash. No other
+// values are supported.
+//
+// Returns 1 on successful verification, 0 on failure.
int RSA_verify(const RSAPublicKey *key,
const uint8_t *signature,
const int len,
const uint8_t *hash,
const int hash_len) {
- switch (key->exponent) {
- case 3:
- return RSA_e_3_verify(key, signature, len, hash, hash_len);
+ uint8_t buf[RSANUMBYTES];
+ int i;
+ const uint8_t* padding_hash;
+
+ if (key->len != RSANUMWORDS) {
+ return 0; // Wrong key passed in.
+ }
+
+ if (len != sizeof(buf)) {
+ return 0; // Wrong input length.
+ }
+
+ if (hash_len != SHA_DIGEST_SIZE &&
+ hash_len != SHA256_DIGEST_SIZE) {
+ return 0; // Unsupported hash.
+ }
+
+ if (key->exponent != 3 && key->exponent != 65537) {
+ return 0; // Unsupported exponent.
+ }
+
+ for (i = 0; i < len; ++i) { // Copy input to local workspace.
+ buf[i] = signature[i];
+ }
+
+ modpow(key, buf); // In-place exponentiation.
+
+ // Xor sha portion, so it all becomes 00 iff equal.
+ for (i = len - hash_len; i < len; ++i) {
+ buf[i] ^= *hash++;
+ }
+
+ // Hash resulting buf, in-place.
+ switch (hash_len) {
+ case SHA_DIGEST_SIZE:
+ padding_hash = kExpectedPadShaRsa2048;
+ SHA_hash(buf, len, buf);
break;
- case 65537:
- return RSA_e_f4_verify(key, signature, len, hash, hash_len);
+ case SHA256_DIGEST_SIZE:
+ padding_hash = kExpectedPadSha256Rsa2048;
+ SHA256_hash(buf, len, buf);
break;
default:
return 0;
}
+
+ // Compare against expected hash value.
+ for (i = 0; i < hash_len; ++i) {
+ if (buf[i] != padding_hash[i]) {
+ return 0;
+ }
+ }
+
+ return 1; // All checked out OK.
}