- 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, mlen = -1, one_index = 0, msg_index;
- unsigned int good, found_one_byte;
- 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)
- md = EVP_sha1();
- 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)
- goto decoding_err;
-
- dblen = num - mdlen - 1;
- db = OPENSSL_malloc(dblen);
- em = OPENSSL_malloc(num);
- if (db == NULL || em == NULL)
- {
- RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1, ERR_R_MALLOC_FAILURE);
- goto cleanup;
- }
-
- /*
- * Always do this zero-padding copy (even when num == flen) to avoid
- * leaking that information. The copy still leaks some side-channel
- * information, but it's impossible to have a fixed memory access
- * pattern since we can't read out of the bounds of |from|.
- *
- * TODO(emilia): Consider porting BN_bn2bin_padded from BoringSSL.
- */
- memset(em, 0, num);
- memcpy(em + num - flen, from, flen);
-
- /*
- * 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.
- */
- if (!good)
- goto decoding_err;
-
- msg_index = one_index + 1;
- mlen = dblen - msg_index;
-
- if (tlen < mlen)
- {
- RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1, RSA_R_DATA_TOO_LARGE);
- mlen = -1;
- }
- else
- {
- memcpy(to, db + msg_index, mlen);
- goto cleanup;
- }
-
-decoding_err:
- /* To avoid chosen ciphertext attacks, the error message should not reveal
- * which kind of decoding error happened. */
- RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1, RSA_R_OAEP_DECODING_ERROR);
-cleanup:
- if (db != NULL) OPENSSL_free(db);
- if (em != NULL) OPENSSL_free(em);
- return mlen;
- }
+ 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, mlen = -1, one_index = 0, msg_index;
+ unsigned int good, found_one_byte;
+ 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)
+ md = EVP_sha1();
+ 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)
+ goto decoding_err;
+
+ dblen = num - mdlen - 1;
+ db = OPENSSL_malloc(dblen);
+ em = OPENSSL_malloc(num);
+ if (db == NULL || em == NULL) {
+ RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1, ERR_R_MALLOC_FAILURE);
+ goto cleanup;
+ }
+
+ /*
+ * Always do this zero-padding copy (even when num == flen) to avoid
+ * leaking that information. The copy still leaks some side-channel
+ * information, but it's impossible to have a fixed memory access
+ * pattern since we can't read out of the bounds of |from|.
+ *
+ * TODO(emilia): Consider porting BN_bn2bin_padded from BoringSSL.
+ */
+ memset(em, 0, num);
+ memcpy(em + num - flen, from, flen);
+
+ /*
+ * 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.
+ */
+ if (!good)
+ goto decoding_err;
+
+ msg_index = one_index + 1;
+ mlen = dblen - msg_index;
+
+ if (tlen < mlen) {
+ RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1, RSA_R_DATA_TOO_LARGE);
+ mlen = -1;
+ } else {
+ memcpy(to, db + msg_index, mlen);
+ goto cleanup;
+ }
+
+ decoding_err:
+ /*
+ * To avoid chosen ciphertext attacks, the error message should not
+ * reveal which kind of decoding error happened.
+ */
+ RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1,
+ RSA_R_OAEP_DECODING_ERROR);
+ cleanup:
+ OPENSSL_free(db);
+ OPENSSL_free(em);
+ return mlen;
+}