/* $OpenBSD: rsa_oaep.c,v 1.22 2014/07/10 22:45:57 jsing Exp $ */ /* 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, * * 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, . * 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 #include #include #if !defined(OPENSSL_NO_SHA) && !defined(OPENSSL_NO_SHA1) #include #include #include #include #include #include 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; } 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; 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, flen); if (RAND_bytes(seed, SHA_DIGEST_LENGTH) <= 0) return 0; dbmask = malloc(emlen - SHA_DIGEST_LENGTH); if (dbmask == NULL) { RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP, ERR_R_MALLOC_FAILURE); return 0; } 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]; 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]; 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 = NULL; unsigned char seed[SHA_DIGEST_LENGTH], phash[SHA_DIGEST_LENGTH]; unsigned char *padded_from; int bad = 0; if (--num < 2 * SHA_DIGEST_LENGTH + 1) /* * 'num' is the length of the modulus, i.e. does not depend * on the particular ciphertext. */ goto decoding_err; lzero = num - flen; if (lzero < 0) { /* * signalling this error immediately after detection might allow * for side-channel attacks (e.g. timing if 'plen' is huge * -- cf. James H. Manger, "A Chosen Ciphertext Attack on RSA * Optimal Asymmetric Encryption Padding (OAEP) [...]", * CRYPTO 2001), so we use a 'bad' flag */ bad = 1; lzero = 0; flen = num; /* don't overflow the memcpy to padded_from */ } dblen = num - SHA_DIGEST_LENGTH; db = malloc(dblen + num); if (db == NULL) { RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP, ERR_R_MALLOC_FAILURE); return -1; } /* * Always do this zero-padding copy (even when lzero == 0) * to avoid leaking timing info about the value of lzero. */ padded_from = db + dblen; memset(padded_from, 0, lzero); memcpy(padded_from + lzero, from, flen); maskeddb = padded_from + SHA_DIGEST_LENGTH; if (MGF1(seed, SHA_DIGEST_LENGTH, maskeddb, dblen)) return -1; for (i = 0; i < SHA_DIGEST_LENGTH; i++) seed[i] ^= padded_from[i]; if (MGF1(db, dblen, seed, SHA_DIGEST_LENGTH)) return -1; for (i = 0; i < dblen; i++) db[i] ^= maskeddb[i]; if (!EVP_Digest((void *)param, plen, phash, NULL, EVP_sha1(), NULL)) return -1; if (CRYPTO_memcmp(db, phash, SHA_DIGEST_LENGTH) != 0 || bad) goto decoding_err; else { for (i = SHA_DIGEST_LENGTH; i < dblen; i++) if (db[i] != 0x00) break; if (i == dblen || db[i] != 0x01) goto decoding_err; else { /* everything looks OK */ mlen = dblen - ++i; if (tlen < mlen) { RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP, RSA_R_DATA_TOO_LARGE); mlen = -1; } else memcpy(to, db + i, mlen); } } free(db); return mlen; 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); free(db); return -1; } 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; } static int MGF1(unsigned char *mask, long len, const unsigned char *seed, long seedlen) { return PKCS1_MGF1(mask, len, seed, seedlen, EVP_sha1()); } #endif