-int PKCS1_MGF1(unsigned char *mask, long len,
- const unsigned char *seed, long seedlen, const EVP_MD *dgst)
- {
- long i, outlen = 0;
- unsigned char cnt[4];
- EVP_MD_CTX c;
- unsigned char md[EVP_MAX_MD_SIZE];
- int mdlen;
- int rv = -1;
-
- EVP_MD_CTX_init(&c);
- mdlen = M_EVP_MD_size(dgst);
- if (mdlen < 0)
- goto err;
- for (i = 0; outlen < len; i++)
- {
- cnt[0] = (unsigned char)((i >> 24) & 255);
- cnt[1] = (unsigned char)((i >> 16) & 255);
- cnt[2] = (unsigned char)((i >> 8)) & 255;
- cnt[3] = (unsigned char)(i & 255);
- if (!EVP_DigestInit_ex(&c,dgst, NULL)
- || !EVP_DigestUpdate(&c, seed, seedlen)
- || !EVP_DigestUpdate(&c, cnt, 4))
- goto err;
- if (outlen + mdlen <= len)
- {
- if (!EVP_DigestFinal_ex(&c, mask + outlen, NULL))
- goto err;
- outlen += mdlen;
- }
- else
- {
- if (!EVP_DigestFinal_ex(&c, md, NULL))
- goto err;
- memcpy(mask + outlen, md, len - outlen);
- outlen = len;
- }
- }
- rv = 0;
- err:
- EVP_MD_CTX_cleanup(&c);
- return rv;
- }
-
-static int MGF1(unsigned char *mask, long len, const unsigned char *seed,
- long seedlen)
- {
- return PKCS1_MGF1(mask, len, seed, seedlen, EVP_sha1());
- }
+int RSA_padding_check_PKCS1_OAEP_mgf1(unsigned char *to, int tlen,
+ const unsigned char *from, int flen,
+ int num, const unsigned char *param,
+ int plen, const EVP_MD *md,
+ const EVP_MD *mgf1md)
+{
+ int i, dblen = 0, mlen = -1, one_index = 0, msg_index;
+ unsigned int good = 0, found_one_byte, mask;
+ const unsigned char *maskedseed, *maskeddb;
+ /*
+ * |em| is the encoded message, zero-padded to exactly |num| bytes: em =
+ * Y || maskedSeed || maskedDB
+ */
+ unsigned char *db = NULL, *em = NULL, seed[EVP_MAX_MD_SIZE],
+ phash[EVP_MAX_MD_SIZE];
+ int mdlen;
+
+ if (md == NULL) {
+#ifndef FIPS_MODE
+ md = EVP_sha1();
+#else
+ RSAerr(0, ERR_R_PASSED_NULL_PARAMETER);
+ return -1;
+#endif
+ }
+
+ if (mgf1md == NULL)
+ mgf1md = md;
+
+ mdlen = EVP_MD_size(md);
+
+ if (tlen <= 0 || flen <= 0)
+ return -1;
+ /*
+ * |num| is the length of the modulus; |flen| is the length of the
+ * encoded message. Therefore, for any |from| that was obtained by
+ * decrypting a ciphertext, we must have |flen| <= |num|. Similarly,
+ * |num| >= 2 * |mdlen| + 2 must hold for the modulus irrespective of
+ * the ciphertext, see PKCS #1 v2.2, section 7.1.2.
+ * This does not leak any side-channel information.
+ */
+ if (num < flen || num < 2 * mdlen + 2) {
+ RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1,
+ RSA_R_OAEP_DECODING_ERROR);
+ return -1;
+ }
+
+ dblen = num - mdlen - 1;
+ db = OPENSSL_malloc(dblen);
+ if (db == NULL) {
+ RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1, ERR_R_MALLOC_FAILURE);
+ goto cleanup;
+ }
+
+ em = OPENSSL_malloc(num);
+ if (em == NULL) {
+ RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1,
+ ERR_R_MALLOC_FAILURE);
+ goto cleanup;
+ }
+
+ /*
+ * Caller is encouraged to pass zero-padded message created with
+ * BN_bn2binpad. Trouble is that since we can't read out of |from|'s
+ * bounds, it's impossible to have an invariant memory access pattern
+ * in case |from| was not zero-padded in advance.
+ */
+ for (from += flen, em += num, i = 0; i < num; i++) {
+ mask = ~constant_time_is_zero(flen);
+ flen -= 1 & mask;
+ from -= 1 & mask;
+ *--em = *from & mask;
+ }
+
+ /*
+ * The first byte must be zero, however we must not leak if this is
+ * true. See James H. Manger, "A Chosen Ciphertext Attack on RSA
+ * Optimal Asymmetric Encryption Padding (OAEP) [...]", CRYPTO 2001).
+ */
+ good = constant_time_is_zero(em[0]);
+
+ maskedseed = em + 1;
+ maskeddb = em + 1 + mdlen;
+
+ if (PKCS1_MGF1(seed, mdlen, maskeddb, dblen, mgf1md))
+ goto cleanup;
+ for (i = 0; i < mdlen; i++)
+ seed[i] ^= maskedseed[i];
+
+ if (PKCS1_MGF1(db, dblen, seed, mdlen, mgf1md))
+ goto cleanup;
+ for (i = 0; i < dblen; i++)
+ db[i] ^= maskeddb[i];
+
+ if (!EVP_Digest((void *)param, plen, phash, NULL, md, NULL))
+ goto cleanup;
+
+ good &= constant_time_is_zero(CRYPTO_memcmp(db, phash, mdlen));
+
+ found_one_byte = 0;
+ for (i = mdlen; i < dblen; i++) {
+ /*
+ * Padding consists of a number of 0-bytes, followed by a 1.
+ */
+ unsigned int equals1 = constant_time_eq(db[i], 1);
+ unsigned int equals0 = constant_time_is_zero(db[i]);
+ one_index = constant_time_select_int(~found_one_byte & equals1,
+ i, one_index);
+ found_one_byte |= equals1;
+ good &= (found_one_byte | equals0);
+ }
+
+ good &= found_one_byte;
+
+ /*
+ * At this point |good| is zero unless the plaintext was valid,
+ * so plaintext-awareness ensures timing side-channels are no longer a
+ * concern.
+ */
+ msg_index = one_index + 1;
+ mlen = dblen - msg_index;
+
+ /*
+ * For good measure, do this check in constant time as well.
+ */
+ good &= constant_time_ge(tlen, mlen);
+
+ /*
+ * Move the result in-place by |dblen|-|mdlen|-1-|mlen| bytes to the left.
+ * Then if |good| move |mlen| bytes from |db|+|mdlen|+1 to |to|.
+ * Otherwise leave |to| unchanged.
+ * Copy the memory back in a way that does not reveal the size of
+ * the data being copied via a timing side channel. This requires copying
+ * parts of the buffer multiple times based on the bits set in the real
+ * length. Clear bits do a non-copy with identical access pattern.
+ * The loop below has overall complexity of O(N*log(N)).
+ */
+ tlen = constant_time_select_int(constant_time_lt(dblen - mdlen - 1, tlen),
+ dblen - mdlen - 1, tlen);
+ for (msg_index = 1; msg_index < dblen - mdlen - 1; msg_index <<= 1) {
+ mask = ~constant_time_eq(msg_index & (dblen - mdlen - 1 - mlen), 0);
+ for (i = mdlen + 1; i < dblen - msg_index; i++)
+ db[i] = constant_time_select_8(mask, db[i + msg_index], db[i]);
+ }
+ for (i = 0; i < tlen; i++) {
+ mask = good & constant_time_lt(i, mlen);
+ to[i] = constant_time_select_8(mask, db[i + mdlen + 1], to[i]);
+ }
+
+#ifndef FIPS_MODE
+ /*
+ * To avoid chosen ciphertext attacks, the error message should not
+ * reveal which kind of decoding error happened.
+ *
+ * This trick doesn't work in the FIPS provider because libcrypto manages
+ * the error stack. Instead we opt not to put an error on the stack at all
+ * in case of padding failure in the FIPS provider.
+ */
+ RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1,
+ RSA_R_OAEP_DECODING_ERROR);
+ err_clear_last_constant_time(1 & good);