156083Skris/* crypto/rsa/rsa_oaep.c */ 2296465Sdelphij/* 3296465Sdelphij * Written by Ulf Moeller. This software is distributed on an "AS IS" basis, 4296465Sdelphij * WITHOUT WARRANTY OF ANY KIND, either express or implied. 5296465Sdelphij */ 656083Skris 789837Skris/* EME-OAEP as defined in RFC 2437 (PKCS #1 v2.0) */ 856083Skris 9296465Sdelphij/* 10296465Sdelphij * See Victor Shoup, "OAEP reconsidered," Nov. 2000, <URL: 11296465Sdelphij * http://www.shoup.net/papers/oaep.ps.Z> for problems with the security 12296465Sdelphij * proof for the original OAEP scheme, which EME-OAEP is based on. A new 13296465Sdelphij * proof can be found in E. Fujisaki, T. Okamoto, D. Pointcheval, J. Stern, 14296465Sdelphij * "RSA-OEAP is Still Alive!", Dec. 2000, <URL: 15296465Sdelphij * http://eprint.iacr.org/2000/061/>. The new proof has stronger requirements 16296465Sdelphij * for the underlying permutation: "partial-one-wayness" instead of 17296465Sdelphij * one-wayness. For the RSA function, this is an equivalent notion. 1889837Skris */ 1989837Skris 20279265Sdelphij#include "constant_time_locl.h" 2189837Skris 22109998Smarkm#if !defined(OPENSSL_NO_SHA) && !defined(OPENSSL_NO_SHA1) 23296465Sdelphij# include <stdio.h> 24296465Sdelphij# include "cryptlib.h" 25296465Sdelphij# include <openssl/bn.h> 26296465Sdelphij# include <openssl/rsa.h> 27296465Sdelphij# include <openssl/evp.h> 28296465Sdelphij# include <openssl/rand.h> 29296465Sdelphij# include <openssl/sha.h> 3056083Skris 3189837Skrisint MGF1(unsigned char *mask, long len, 32296465Sdelphij const unsigned char *seed, long seedlen); 3356083Skris 3456083Skrisint RSA_padding_add_PKCS1_OAEP(unsigned char *to, int tlen, 35296465Sdelphij const unsigned char *from, int flen, 36296465Sdelphij const unsigned char *param, int plen) 37296465Sdelphij{ 38296465Sdelphij int i, emlen = tlen - 1; 39296465Sdelphij unsigned char *db, *seed; 40296465Sdelphij unsigned char *dbmask, seedmask[SHA_DIGEST_LENGTH]; 4156083Skris 42296465Sdelphij if (flen > emlen - 2 * SHA_DIGEST_LENGTH - 1) { 43296465Sdelphij RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP, 44296465Sdelphij RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE); 45296465Sdelphij return 0; 46296465Sdelphij } 4756083Skris 48296465Sdelphij if (emlen < 2 * SHA_DIGEST_LENGTH + 1) { 49296465Sdelphij RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP, RSA_R_KEY_SIZE_TOO_SMALL); 50296465Sdelphij return 0; 51296465Sdelphij } 5256083Skris 53296465Sdelphij to[0] = 0; 54296465Sdelphij seed = to + 1; 55296465Sdelphij db = to + SHA_DIGEST_LENGTH + 1; 5689837Skris 57296465Sdelphij EVP_Digest((void *)param, plen, db, NULL, EVP_sha1(), NULL); 58296465Sdelphij memset(db + SHA_DIGEST_LENGTH, 0, 59296465Sdelphij emlen - flen - 2 * SHA_DIGEST_LENGTH - 1); 60296465Sdelphij db[emlen - flen - SHA_DIGEST_LENGTH - 1] = 0x01; 61296465Sdelphij memcpy(db + emlen - flen - SHA_DIGEST_LENGTH, from, (unsigned int)flen); 62296465Sdelphij if (RAND_bytes(seed, SHA_DIGEST_LENGTH) <= 0) 63296465Sdelphij return 0; 64296465Sdelphij# ifdef PKCS_TESTVECT 65296465Sdelphij memcpy(seed, 66296465Sdelphij "\xaa\xfd\x12\xf6\x59\xca\xe6\x34\x89\xb4\x79\xe5\x07\x6d\xde\xc2\xf0\x6c\xb5\x8f", 67296465Sdelphij 20); 68296465Sdelphij# endif 6956083Skris 70296465Sdelphij dbmask = OPENSSL_malloc(emlen - SHA_DIGEST_LENGTH); 71296465Sdelphij if (dbmask == NULL) { 72296465Sdelphij RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP, ERR_R_MALLOC_FAILURE); 73296465Sdelphij return 0; 74296465Sdelphij } 75205128Ssimon 76296465Sdelphij MGF1(dbmask, emlen - SHA_DIGEST_LENGTH, seed, SHA_DIGEST_LENGTH); 77296465Sdelphij for (i = 0; i < emlen - SHA_DIGEST_LENGTH; i++) 78296465Sdelphij db[i] ^= dbmask[i]; 7956083Skris 80296465Sdelphij MGF1(seedmask, SHA_DIGEST_LENGTH, db, emlen - SHA_DIGEST_LENGTH); 81296465Sdelphij for (i = 0; i < SHA_DIGEST_LENGTH; i++) 82296465Sdelphij seed[i] ^= seedmask[i]; 8356083Skris 84296465Sdelphij OPENSSL_free(dbmask); 85296465Sdelphij return 1; 86296465Sdelphij} 8756083Skris 8856083Skrisint RSA_padding_check_PKCS1_OAEP(unsigned char *to, int tlen, 89296465Sdelphij const unsigned char *from, int flen, int num, 90296465Sdelphij const unsigned char *param, int plen) 91296465Sdelphij{ 92296465Sdelphij int i, dblen, mlen = -1, one_index = 0, msg_index; 93296465Sdelphij unsigned int good, found_one_byte; 94296465Sdelphij const unsigned char *maskedseed, *maskeddb; 95296465Sdelphij /* 96296465Sdelphij * |em| is the encoded message, zero-padded to exactly |num| bytes: em = 97296465Sdelphij * Y || maskedSeed || maskedDB 98296465Sdelphij */ 99296465Sdelphij unsigned char *db = NULL, *em = NULL, seed[EVP_MAX_MD_SIZE], 100296465Sdelphij phash[EVP_MAX_MD_SIZE]; 10156083Skris 102296465Sdelphij if (tlen <= 0 || flen <= 0) 103296465Sdelphij return -1; 104279265Sdelphij 105296465Sdelphij /* 106296465Sdelphij * |num| is the length of the modulus; |flen| is the length of the 107296465Sdelphij * encoded message. Therefore, for any |from| that was obtained by 108296465Sdelphij * decrypting a ciphertext, we must have |flen| <= |num|. Similarly, 109296465Sdelphij * num < 2 * SHA_DIGEST_LENGTH + 2 must hold for the modulus 110296465Sdelphij * irrespective of the ciphertext, see PKCS #1 v2.2, section 7.1.2. 111296465Sdelphij * This does not leak any side-channel information. 112296465Sdelphij */ 113296465Sdelphij if (num < flen || num < 2 * SHA_DIGEST_LENGTH + 2) 114296465Sdelphij goto decoding_err; 11556083Skris 116296465Sdelphij dblen = num - SHA_DIGEST_LENGTH - 1; 117296465Sdelphij db = OPENSSL_malloc(dblen); 118296465Sdelphij em = OPENSSL_malloc(num); 119296465Sdelphij if (db == NULL || em == NULL) { 120296465Sdelphij RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP, ERR_R_MALLOC_FAILURE); 121296465Sdelphij goto cleanup; 122296465Sdelphij } 12356083Skris 124296465Sdelphij /* 125296465Sdelphij * Always do this zero-padding copy (even when num == flen) to avoid 126296465Sdelphij * leaking that information. The copy still leaks some side-channel 127296465Sdelphij * information, but it's impossible to have a fixed memory access 128296465Sdelphij * pattern since we can't read out of the bounds of |from|. 129296465Sdelphij * 130296465Sdelphij * TODO(emilia): Consider porting BN_bn2bin_padded from BoringSSL. 131296465Sdelphij */ 132296465Sdelphij memset(em, 0, num); 133296465Sdelphij memcpy(em + num - flen, from, flen); 134194206Ssimon 135296465Sdelphij /* 136296465Sdelphij * The first byte must be zero, however we must not leak if this is 137296465Sdelphij * true. See James H. Manger, "A Chosen Ciphertext Attack on RSA 138296465Sdelphij * Optimal Asymmetric Encryption Padding (OAEP) [...]", CRYPTO 2001). 139296465Sdelphij */ 140296465Sdelphij good = constant_time_is_zero(em[0]); 141194206Ssimon 142296465Sdelphij maskedseed = em + 1; 143296465Sdelphij maskeddb = em + 1 + SHA_DIGEST_LENGTH; 144279265Sdelphij 145296465Sdelphij MGF1(seed, SHA_DIGEST_LENGTH, maskeddb, dblen); 146296465Sdelphij for (i = 0; i < SHA_DIGEST_LENGTH; i++) 147296465Sdelphij seed[i] ^= maskedseed[i]; 148279265Sdelphij 149296465Sdelphij MGF1(db, dblen, seed, SHA_DIGEST_LENGTH); 150296465Sdelphij for (i = 0; i < dblen; i++) 151296465Sdelphij db[i] ^= maskeddb[i]; 15289837Skris 153296465Sdelphij EVP_Digest((void *)param, plen, phash, NULL, EVP_sha1(), NULL); 15489837Skris 155296465Sdelphij good &= 156296465Sdelphij constant_time_is_zero(CRYPTO_memcmp(db, phash, SHA_DIGEST_LENGTH)); 157279265Sdelphij 158296465Sdelphij found_one_byte = 0; 159296465Sdelphij for (i = SHA_DIGEST_LENGTH; i < dblen; i++) { 160296465Sdelphij /* 161296465Sdelphij * Padding consists of a number of 0-bytes, followed by a 1. 162296465Sdelphij */ 163296465Sdelphij unsigned int equals1 = constant_time_eq(db[i], 1); 164296465Sdelphij unsigned int equals0 = constant_time_is_zero(db[i]); 165296465Sdelphij one_index = constant_time_select_int(~found_one_byte & equals1, 166296465Sdelphij i, one_index); 167296465Sdelphij found_one_byte |= equals1; 168296465Sdelphij good &= (found_one_byte | equals0); 169296465Sdelphij } 170279265Sdelphij 171296465Sdelphij good &= found_one_byte; 172279265Sdelphij 173296465Sdelphij /* 174296465Sdelphij * At this point |good| is zero unless the plaintext was valid, 175296465Sdelphij * so plaintext-awareness ensures timing side-channels are no longer a 176296465Sdelphij * concern. 177296465Sdelphij */ 178296465Sdelphij if (!good) 179296465Sdelphij goto decoding_err; 180279265Sdelphij 181296465Sdelphij msg_index = one_index + 1; 182296465Sdelphij mlen = dblen - msg_index; 183279265Sdelphij 184296465Sdelphij if (tlen < mlen) { 185296465Sdelphij RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP, RSA_R_DATA_TOO_LARGE); 186296465Sdelphij mlen = -1; 187296465Sdelphij } else { 188296465Sdelphij memcpy(to, db + msg_index, mlen); 189296465Sdelphij goto cleanup; 190296465Sdelphij } 19179998Skris 192296465Sdelphij decoding_err: 193296465Sdelphij /* 194296465Sdelphij * To avoid chosen ciphertext attacks, the error message should not 195296465Sdelphij * reveal which kind of decoding error happened. 196296465Sdelphij */ 197296465Sdelphij RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP, RSA_R_OAEP_DECODING_ERROR); 198296465Sdelphij cleanup: 199296465Sdelphij if (db != NULL) 200296465Sdelphij OPENSSL_free(db); 201296465Sdelphij if (em != NULL) 202296465Sdelphij OPENSSL_free(em); 203296465Sdelphij return mlen; 204296465Sdelphij} 20556083Skris 206160814Ssimonint PKCS1_MGF1(unsigned char *mask, long len, 207296465Sdelphij const unsigned char *seed, long seedlen, const EVP_MD *dgst) 208296465Sdelphij{ 209296465Sdelphij long i, outlen = 0; 210296465Sdelphij unsigned char cnt[4]; 211296465Sdelphij EVP_MD_CTX c; 212296465Sdelphij unsigned char md[EVP_MAX_MD_SIZE]; 213296465Sdelphij int mdlen; 21456083Skris 215296465Sdelphij EVP_MD_CTX_init(&c); 216296465Sdelphij mdlen = M_EVP_MD_size(dgst); 217296465Sdelphij for (i = 0; outlen < len; i++) { 218296465Sdelphij cnt[0] = (unsigned char)((i >> 24) & 255); 219296465Sdelphij cnt[1] = (unsigned char)((i >> 16) & 255); 220296465Sdelphij cnt[2] = (unsigned char)((i >> 8)) & 255; 221296465Sdelphij cnt[3] = (unsigned char)(i & 255); 222296465Sdelphij EVP_DigestInit_ex(&c, dgst, NULL); 223296465Sdelphij EVP_DigestUpdate(&c, seed, seedlen); 224296465Sdelphij EVP_DigestUpdate(&c, cnt, 4); 225296465Sdelphij if (outlen + mdlen <= len) { 226296465Sdelphij EVP_DigestFinal_ex(&c, mask + outlen, NULL); 227296465Sdelphij outlen += mdlen; 228296465Sdelphij } else { 229296465Sdelphij EVP_DigestFinal_ex(&c, md, NULL); 230296465Sdelphij memcpy(mask + outlen, md, len - outlen); 231296465Sdelphij outlen = len; 232296465Sdelphij } 233296465Sdelphij } 234296465Sdelphij EVP_MD_CTX_cleanup(&c); 235296465Sdelphij return 0; 236296465Sdelphij} 237160814Ssimon 238296465Sdelphijint MGF1(unsigned char *mask, long len, const unsigned char *seed, 239296465Sdelphij long seedlen) 240296465Sdelphij{ 241296465Sdelphij return PKCS1_MGF1(mask, len, seed, seedlen, EVP_sha1()); 242296465Sdelphij} 24356083Skris#endif 244