/* crypto/rsa/rsa_oaep.c */ /* * Written by Ulf Moeller. This software is distributed on an "AS IS" basis, * WITHOUT WARRANTY OF ANY KIND, either express or implied. */ /* EME-OAEP as defined in RFC 2437 (PKCS #1 v2.0) */ /* * See Victor Shoup, "OAEP reconsidered," Nov. 2000, <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. 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(OPENSSL_NO_SHA) && !defined(OPENSSL_NO_SHA1) # include <stdio.h> # include "cryptlib.h" # include <openssl/bn.h> # include <openssl/rsa.h> # include <openssl/evp.h> # include <openssl/rand.h> # include <openssl/sha.h> int RSA_padding_add_PKCS1_OAEP(unsigned char *to, int tlen, const unsigned char *from, int flen, const unsigned char *param, int plen) { return RSA_padding_add_PKCS1_OAEP_mgf1(to, tlen, from, flen, param, plen, NULL, NULL); } int RSA_padding_add_PKCS1_OAEP_mgf1(unsigned char *to, int tlen, const unsigned char *from, int flen, const unsigned char *param, int plen, const EVP_MD *md, const EVP_MD *mgf1md) { int i, emlen = tlen - 1; unsigned char *db, *seed; unsigned char *dbmask, seedmask[EVP_MAX_MD_SIZE]; int mdlen; if (md == NULL) md = EVP_sha1(); if (mgf1md == NULL) mgf1md = md; mdlen = EVP_MD_size(md); if (flen > emlen - 2 * mdlen - 1) { RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP_MGF1, RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE); return 0; } if (emlen < 2 * mdlen + 1) { RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP_MGF1, RSA_R_KEY_SIZE_TOO_SMALL); return 0; } to[0] = 0; seed = to + 1; db = to + mdlen + 1; if (!EVP_Digest((void *)param, plen, db, NULL, md, NULL)) return 0; memset(db + mdlen, 0, emlen - flen - 2 * mdlen - 1); db[emlen - flen - mdlen - 1] = 0x01; memcpy(db + emlen - flen - mdlen, from, (unsigned int)flen); if (RAND_bytes(seed, mdlen) <= 0) return 0; # ifdef PKCS_TESTVECT memcpy(seed, "\xaa\xfd\x12\xf6\x59\xca\xe6\x34\x89\xb4\x79\xe5\x07\x6d\xde\xc2\xf0\x6c\xb5\x8f", 20); # endif dbmask = OPENSSL_malloc(emlen - mdlen); if (dbmask == NULL) { RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP_MGF1, ERR_R_MALLOC_FAILURE); return 0; } if (PKCS1_MGF1(dbmask, emlen - mdlen, seed, mdlen, mgf1md) < 0) return 0; for (i = 0; i < emlen - mdlen; i++) db[i] ^= dbmask[i]; if (PKCS1_MGF1(seedmask, mdlen, db, emlen - mdlen, mgf1md) < 0) return 0; for (i = 0; i < mdlen; 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) { return RSA_padding_check_PKCS1_OAEP_mgf1(to, tlen, from, flen, num, param, plen, NULL, NULL); } 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, 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; } 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 = 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; } #endif