* <URL: http://www.shoup.net/papers/oaep.ps.Z>
* for problems with the security proof for the
* original OAEP scheme, which EME-OAEP is based on.
- *
- * Note that for RSA OAEP a security proof in the
- * random oracle model *does* exist if 160 < log_2(N/e);
- * cf. section 7.2 ("But RSA-OAEP with exponent 3 is
- * provably secure") of Shoup's paper. (The slight
- * differences between the OAEP definition used by Shoup
- * and OAEP as defined in RFC 2437 should not affect
- * this result.)
+ *
+ * A new proof can be found in E. Fujisaki, T. Okamoto,
+ * D. Pointcheval, J. Stern, "RSA-OEAP is Still Alive!",
+ * Dec. 2000, <URL: http://eprint.iacr.org/2000/061/>.
+ * The new proof has stronger requirements for the
+ * underlying permutation: "partial-one-wayness" instead
+ * of one-wayness. For the RSA function, this is
+ * an equivalent notion.
*/
+#include "constant_time_locl.h"
-#if !defined(NO_SHA) && !defined(NO_SHA1)
+#if !defined(OPENSSL_NO_SHA) && !defined(OPENSSL_NO_SHA1)
#include <stdio.h>
#include "cryptlib.h"
#include <openssl/bn.h>
#include <openssl/rsa.h>
-#include <openssl/sha.h>
+#include <openssl/evp.h>
#include <openssl/rand.h>
+#include <openssl/sha.h>
-int MGF1(unsigned char *mask, long len,
+static int MGF1(unsigned char *mask, long len,
const unsigned char *seed, long seedlen);
int RSA_padding_add_PKCS1_OAEP(unsigned char *to, int tlen,
const unsigned char *from, int flen,
const unsigned char *param, int plen)
- {
- int i, emlen = tlen - 1;
- unsigned char *db, *seed;
- unsigned char *dbmask, seedmask[SHA_DIGEST_LENGTH];
-
- if (flen > emlen - 2 * SHA_DIGEST_LENGTH - 1)
{
- RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP,
- RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE);
- return (0);
- }
+ int i, emlen = tlen - 1;
+ unsigned char *db, *seed;
+ unsigned char *dbmask, seedmask[SHA_DIGEST_LENGTH];
- if (emlen < 2 * SHA_DIGEST_LENGTH + 1)
- {
- RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP, RSA_R_KEY_SIZE_TOO_SMALL);
- return (0);
- }
-
- dbmask = OPENSSL_malloc(emlen - SHA_DIGEST_LENGTH);
- if (dbmask == NULL)
- {
- RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP, ERR_R_MALLOC_FAILURE);
- return (0);
- }
+ if (flen > emlen - 2 * SHA_DIGEST_LENGTH - 1)
+ {
+ RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP,
+ RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE);
+ return 0;
+ }
+
+ if (emlen < 2 * SHA_DIGEST_LENGTH + 1)
+ {
+ RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP, RSA_R_KEY_SIZE_TOO_SMALL);
+ return 0;
+ }
+
+ to[0] = 0;
+ seed = to + 1;
+ db = to + SHA_DIGEST_LENGTH + 1;
- to[0] = 0;
- seed = to + 1;
- db = to + SHA_DIGEST_LENGTH + 1;
-
- SHA1(param, plen, db);
- memset(db + SHA_DIGEST_LENGTH, 0,
- emlen - flen - 2 * SHA_DIGEST_LENGTH - 1);
- db[emlen - flen - SHA_DIGEST_LENGTH - 1] = 0x01;
- memcpy(db + emlen - flen - SHA_DIGEST_LENGTH, from, (unsigned int) flen);
- if (RAND_bytes(seed, SHA_DIGEST_LENGTH) <= 0)
- return (0);
+ if (!EVP_Digest((void *)param, plen, db, NULL, EVP_sha1(), NULL))
+ return 0;
+ memset(db + SHA_DIGEST_LENGTH, 0,
+ emlen - flen - 2 * SHA_DIGEST_LENGTH - 1);
+ db[emlen - flen - SHA_DIGEST_LENGTH - 1] = 0x01;
+ memcpy(db + emlen - flen - SHA_DIGEST_LENGTH, from, (unsigned int) flen);
+ if (RAND_bytes(seed, SHA_DIGEST_LENGTH) <= 0)
+ return 0;
#ifdef PKCS_TESTVECT
- memcpy(seed,
+ memcpy(seed,
"\xaa\xfd\x12\xf6\x59\xca\xe6\x34\x89\xb4\x79\xe5\x07\x6d\xde\xc2\xf0\x6c\xb5\x8f",
20);
#endif
- MGF1(dbmask, emlen - SHA_DIGEST_LENGTH, seed, SHA_DIGEST_LENGTH);
- for (i = 0; i < emlen - SHA_DIGEST_LENGTH; i++)
- db[i] ^= dbmask[i];
+ dbmask = OPENSSL_malloc(emlen - SHA_DIGEST_LENGTH);
+ if (dbmask == NULL)
+ {
+ RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP, ERR_R_MALLOC_FAILURE);
+ return 0;
+ }
- MGF1(seedmask, SHA_DIGEST_LENGTH, db, emlen - SHA_DIGEST_LENGTH);
- for (i = 0; i < SHA_DIGEST_LENGTH; i++)
- seed[i] ^= seedmask[i];
+ if (MGF1(dbmask, emlen - SHA_DIGEST_LENGTH, seed, SHA_DIGEST_LENGTH) < 0)
+ return 0;
+ for (i = 0; i < emlen - SHA_DIGEST_LENGTH; i++)
+ db[i] ^= dbmask[i];
- OPENSSL_free(dbmask);
- return (1);
- }
+ if (MGF1(seedmask, SHA_DIGEST_LENGTH, db, emlen - SHA_DIGEST_LENGTH) < 0)
+ return 0;
+ for (i = 0; i < SHA_DIGEST_LENGTH; i++)
+ seed[i] ^= seedmask[i];
+
+ OPENSSL_free(dbmask);
+ return 1;
+ }
int RSA_padding_check_PKCS1_OAEP(unsigned char *to, int tlen,
const unsigned char *from, int flen, int num,
const unsigned char *param, int plen)
- {
- int i, dblen, mlen = -1;
- const unsigned char *maskeddb;
- int lzero;
- unsigned char *db, seed[SHA_DIGEST_LENGTH], phash[SHA_DIGEST_LENGTH];
-
- if (--num < 2 * SHA_DIGEST_LENGTH + 1)
{
- RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP, RSA_R_OAEP_DECODING_ERROR);
- return (-1);
- }
+ 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];
- dblen = num - SHA_DIGEST_LENGTH;
- db = OPENSSL_malloc(dblen);
- if (db == NULL)
- {
- RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP, ERR_R_MALLOC_FAILURE);
- return (-1);
- }
+ if (tlen <= 0 || flen <= 0)
+ return -1;
- lzero = num - flen;
- maskeddb = from - lzero + SHA_DIGEST_LENGTH;
-
- MGF1(seed, SHA_DIGEST_LENGTH, maskeddb, dblen);
- for (i = lzero; i < SHA_DIGEST_LENGTH; i++)
- seed[i] ^= from[i - lzero];
-
- MGF1(db, dblen, seed, SHA_DIGEST_LENGTH);
- for (i = 0; i < dblen; i++)
- db[i] ^= maskeddb[i];
+ /*
+ * |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 * SHA_DIGEST_LENGTH + 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 * SHA_DIGEST_LENGTH + 2)
+ goto decoding_err;
- SHA1(param, plen, phash);
+ dblen = num - SHA_DIGEST_LENGTH - 1;
+ db = OPENSSL_malloc(dblen);
+ em = OPENSSL_malloc(num);
+ if (db == NULL || em == NULL)
+ {
+ RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP, ERR_R_MALLOC_FAILURE);
+ goto cleanup;
+ }
- if (memcmp(db, phash, SHA_DIGEST_LENGTH) != 0)
- RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP, RSA_R_OAEP_DECODING_ERROR);
- else
- {
+ /*
+ * 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 + SHA_DIGEST_LENGTH;
+
+ if (MGF1(seed, SHA_DIGEST_LENGTH, maskeddb, dblen))
+ goto cleanup;
+ for (i = 0; i < SHA_DIGEST_LENGTH; i++)
+ seed[i] ^= maskedseed[i];
+
+ if (MGF1(db, dblen, seed, SHA_DIGEST_LENGTH))
+ goto cleanup;
+ for (i = 0; i < dblen; i++)
+ db[i] ^= maskeddb[i];
+
+ if (!EVP_Digest((void *)param, plen, phash, NULL, EVP_sha1(), NULL))
+ goto cleanup;
+
+ good &= constant_time_is_zero(CRYPTO_memcmp(db, phash, SHA_DIGEST_LENGTH));
+
+ found_one_byte = 0;
for (i = SHA_DIGEST_LENGTH; i < dblen; i++)
- if (db[i] != 0x00)
- break;
- if (db[i] != 0x01 || i++ >= dblen)
- RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP,
- RSA_R_OAEP_DECODING_ERROR);
- else
- {
- mlen = dblen - i;
- if (tlen < mlen)
{
- RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP, RSA_R_DATA_TOO_LARGE);
+ /* 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, RSA_R_DATA_TOO_LARGE);
mlen = -1;
}
- else
- memcpy(to, db + i, mlen);
- }
+ 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, RSA_R_OAEP_DECODING_ERROR);
+cleanup:
+ if (db != NULL) OPENSSL_free(db);
+ if (em != NULL) OPENSSL_free(em);
+ return mlen;
}
- OPENSSL_free(db);
- return (mlen);
- }
-
-int MGF1(unsigned char *mask, long len,
- const unsigned char *seed, long seedlen)
- {
- long i, outlen = 0;
- unsigned char cnt[4];
- SHA_CTX c;
- unsigned char md[SHA_DIGEST_LENGTH];
-
- for (i = 0; outlen < len; i++)
+
+int PKCS1_MGF1(unsigned char *mask, long len,
+ const unsigned char *seed, long seedlen, const EVP_MD *dgst)
{
- cnt[0] = (i >> 24) & 255, cnt[1] = (i >> 16) & 255,
- cnt[2] = (i >> 8) & 255, cnt[3] = i & 255;
- SHA1_Init(&c);
- SHA1_Update(&c, seed, seedlen);
- SHA1_Update(&c, cnt, 4);
- if (outlen + SHA_DIGEST_LENGTH <= len)
- {
- SHA1_Final(mask + outlen, &c);
- outlen += SHA_DIGEST_LENGTH;
- }
- else
- {
- SHA1_Final(md, &c);
- memcpy(mask + outlen, md, len - outlen);
- outlen = len;
- }
+ 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 = 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());
}
- return (0);
- }
#endif
projects / openssl.git / blobdiff