/* * Copyright 1999-2021 The OpenSSL Project Authors. All Rights Reserved. * * Licensed under the Apache License 2.0 (the "License"). You may not use * this file except in compliance with the License. You can obtain a copy * in the file LICENSE in the source distribution or at * https://www.openssl.org/source/license.html */ /* 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. */ /* * RSA low level APIs are deprecated for public use, but still ok for * internal use. */ #include "internal/deprecated.h" #include "internal/constant_time.h" #include #include "internal/cryptlib.h" #include #include #include #include #include "rsa_local.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 ossl_rsa_padding_add_PKCS1_OAEP_mgf1_ex(NULL, to, tlen, from, flen, param, plen, NULL, NULL); } /* * Perform the padding as per NIST 800-56B 7.2.2.3 * from (K) is the key material. * param (A) is the additional input. * Step numbers are included here but not in the constant time inverse below * to avoid complicating an already difficult enough function. */ int ossl_rsa_padding_add_PKCS1_OAEP_mgf1_ex(OSSL_LIB_CTX *libctx, 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 rv = 0; int i, emlen = tlen - 1; unsigned char *db, *seed; unsigned char *dbmask = NULL; unsigned char seedmask[EVP_MAX_MD_SIZE]; int mdlen, dbmask_len = 0; if (md == NULL) { #ifndef FIPS_MODULE md = EVP_sha1(); #else ERR_raise(ERR_LIB_RSA, ERR_R_PASSED_NULL_PARAMETER); return 0; #endif } if (mgf1md == NULL) mgf1md = md; mdlen = EVP_MD_get_size(md); if (mdlen <= 0) { ERR_raise(ERR_LIB_RSA, RSA_R_INVALID_LENGTH); return 0; } /* step 2b: check KLen > nLen - 2 HLen - 2 */ if (flen > emlen - 2 * mdlen - 1) { ERR_raise(ERR_LIB_RSA, RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE); return 0; } if (emlen < 2 * mdlen + 1) { ERR_raise(ERR_LIB_RSA, RSA_R_KEY_SIZE_TOO_SMALL); return 0; } /* step 3i: EM = 00000000 || maskedMGF || maskedDB */ to[0] = 0; seed = to + 1; db = to + mdlen + 1; /* step 3a: hash the additional input */ if (!EVP_Digest((void *)param, plen, db, NULL, md, NULL)) goto err; /* step 3b: zero bytes array of length nLen - KLen - 2 HLen -2 */ memset(db + mdlen, 0, emlen - flen - 2 * mdlen - 1); /* step 3c: DB = HA || PS || 00000001 || K */ db[emlen - flen - mdlen - 1] = 0x01; memcpy(db + emlen - flen - mdlen, from, (unsigned int)flen); /* step 3d: generate random byte string */ if (RAND_bytes_ex(libctx, seed, mdlen, 0) <= 0) goto err; dbmask_len = emlen - mdlen; dbmask = OPENSSL_malloc(dbmask_len); if (dbmask == NULL) goto err; /* step 3e: dbMask = MGF(mgfSeed, nLen - HLen - 1) */ if (PKCS1_MGF1(dbmask, dbmask_len, seed, mdlen, mgf1md) < 0) goto err; /* step 3f: maskedDB = DB XOR dbMask */ for (i = 0; i < dbmask_len; i++) db[i] ^= dbmask[i]; /* step 3g: mgfSeed = MGF(maskedDB, HLen) */ if (PKCS1_MGF1(seedmask, mdlen, db, dbmask_len, mgf1md) < 0) goto err; /* stepo 3h: maskedMGFSeed = mgfSeed XOR mgfSeedMask */ for (i = 0; i < mdlen; i++) seed[i] ^= seedmask[i]; rv = 1; err: OPENSSL_cleanse(seedmask, sizeof(seedmask)); OPENSSL_clear_free(dbmask, dbmask_len); return rv; } 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) { return ossl_rsa_padding_add_PKCS1_OAEP_mgf1_ex(NULL, to, tlen, from, flen, param, plen, md, mgf1md); } 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 = 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_MODULE md = EVP_sha1(); #else ERR_raise(ERR_LIB_RSA, ERR_R_PASSED_NULL_PARAMETER); return -1; #endif } if (mgf1md == NULL) mgf1md = md; mdlen = EVP_MD_get_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) { ERR_raise(ERR_LIB_RSA, RSA_R_OAEP_DECODING_ERROR); return -1; } dblen = num - mdlen - 1; db = OPENSSL_malloc(dblen); if (db == NULL) goto cleanup; em = OPENSSL_malloc(num); if (em == NULL) 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_MODULE /* * 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. */ ERR_raise(ERR_LIB_RSA, RSA_R_OAEP_DECODING_ERROR); err_clear_last_constant_time(1 & good); #endif cleanup: OPENSSL_cleanse(seed, sizeof(seed)); OPENSSL_clear_free(db, dblen); OPENSSL_clear_free(em, num); return constant_time_select_int(good, mlen, -1); } /* * Mask Generation Function corresponding to section 7.2.2.2 of NIST SP 800-56B. * The variables are named differently to NIST: * mask (T) and len (maskLen)are the returned mask. * seed (mgfSeed). * The range checking steps inm the process are performed outside. */ 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 = EVP_MD_CTX_new(); unsigned char md[EVP_MAX_MD_SIZE]; int mdlen; int rv = -1; if (c == NULL) goto err; mdlen = EVP_MD_get_size(dgst); if (mdlen < 0) goto err; /* step 4 */ for (i = 0; outlen < len; i++) { /* step 4a: D = I2BS(counter, 4) */ 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); /* step 4b: T =T || hash(mgfSeed || D) */ 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: OPENSSL_cleanse(md, sizeof(md)); EVP_MD_CTX_free(c); return rv; }