rsa_oaep.c revision 348343
10SN/A/* crypto/rsa/rsa_oaep.c */ 22362SN/A/* 30SN/A * Written by Ulf Moeller. This software is distributed on an "AS IS" basis, 40SN/A * WITHOUT WARRANTY OF ANY KIND, either express or implied. 50SN/A */ 60SN/A 72362SN/A/* EME-OAEP as defined in RFC 2437 (PKCS #1 v2.0) */ 80SN/A 92362SN/A/* 100SN/A * See Victor Shoup, "OAEP reconsidered," Nov. 2000, <URL: 110SN/A * http://www.shoup.net/papers/oaep.ps.Z> for problems with the security 120SN/A * proof for the original OAEP scheme, which EME-OAEP is based on. A new 130SN/A * proof can be found in E. Fujisaki, T. Okamoto, D. Pointcheval, J. Stern, 140SN/A * "RSA-OEAP is Still Alive!", Dec. 2000, <URL: 150SN/A * http://eprint.iacr.org/2000/061/>. The new proof has stronger requirements 160SN/A * for the underlying permutation: "partial-one-wayness" instead of 170SN/A * one-wayness. For the RSA function, this is an equivalent notion. 180SN/A */ 190SN/A 200SN/A#include "constant_time_locl.h" 212362SN/A 222362SN/A#if !defined(OPENSSL_NO_SHA) && !defined(OPENSSL_NO_SHA1) 232362SN/A# include <stdio.h> 240SN/A# include "cryptlib.h" 250SN/A# include <openssl/bn.h> 260SN/A# include <openssl/rsa.h> 270SN/A# include <openssl/evp.h> 280SN/A# include <openssl/rand.h> 290SN/A# include <openssl/sha.h> 300SN/A 310SN/Aint RSA_padding_add_PKCS1_OAEP(unsigned char *to, int tlen, 320SN/A const unsigned char *from, int flen, 330SN/A const unsigned char *param, int plen) 340SN/A{ 350SN/A return RSA_padding_add_PKCS1_OAEP_mgf1(to, tlen, from, flen, 360SN/A param, plen, NULL, NULL); 370SN/A} 380SN/A 390SN/Aint RSA_padding_add_PKCS1_OAEP_mgf1(unsigned char *to, int tlen, 400SN/A const unsigned char *from, int flen, 410SN/A const unsigned char *param, int plen, 420SN/A const EVP_MD *md, const EVP_MD *mgf1md) 430SN/A{ 440SN/A int i, emlen = tlen - 1; 450SN/A unsigned char *db, *seed; 460SN/A unsigned char *dbmask, seedmask[EVP_MAX_MD_SIZE]; 470SN/A int mdlen; 480SN/A 490SN/A if (md == NULL) 500SN/A md = EVP_sha1(); 510SN/A if (mgf1md == NULL) 520SN/A mgf1md = md; 530SN/A 540SN/A mdlen = EVP_MD_size(md); 550SN/A 560SN/A if (flen > emlen - 2 * mdlen - 1) { 570SN/A RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP_MGF1, 580SN/A RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE); 590SN/A return 0; 600SN/A } 610SN/A 620SN/A if (emlen < 2 * mdlen + 1) { 630SN/A RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP_MGF1, 640SN/A RSA_R_KEY_SIZE_TOO_SMALL); 650SN/A return 0; 660SN/A } 670SN/A 680SN/A to[0] = 0; 690SN/A seed = to + 1; 700SN/A db = to + mdlen + 1; 710SN/A 720SN/A if (!EVP_Digest((void *)param, plen, db, NULL, md, NULL)) 730SN/A return 0; 740SN/A memset(db + mdlen, 0, emlen - flen - 2 * mdlen - 1); 750SN/A db[emlen - flen - mdlen - 1] = 0x01; 760SN/A memcpy(db + emlen - flen - mdlen, from, (unsigned int)flen); 770SN/A if (RAND_bytes(seed, mdlen) <= 0) 780SN/A return 0; 790SN/A# ifdef PKCS_TESTVECT 800SN/A memcpy(seed, 810SN/A "\xaa\xfd\x12\xf6\x59\xca\xe6\x34\x89\xb4\x79\xe5\x07\x6d\xde\xc2\xf0\x6c\xb5\x8f", 820SN/A 20); 830SN/A# endif 840SN/A 8512489Savstepan dbmask = OPENSSL_malloc(emlen - mdlen); 860SN/A if (dbmask == NULL) { 870SN/A RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP_MGF1, ERR_R_MALLOC_FAILURE); 880SN/A return 0; 890SN/A } 900SN/A 910SN/A if (PKCS1_MGF1(dbmask, emlen - mdlen, seed, mdlen, mgf1md) < 0) 920SN/A goto err; 930SN/A for (i = 0; i < emlen - mdlen; i++) 940SN/A db[i] ^= dbmask[i]; 950SN/A 960SN/A if (PKCS1_MGF1(seedmask, mdlen, db, emlen - mdlen, mgf1md) < 0) 970SN/A goto err; 980SN/A for (i = 0; i < mdlen; i++) 990SN/A seed[i] ^= seedmask[i]; 1000SN/A 1010SN/A OPENSSL_free(dbmask); 1020SN/A return 1; 1030SN/A 1040SN/A err: 1050SN/A OPENSSL_free(dbmask); 1060SN/A return 0; 1070SN/A} 1080SN/A 1090SN/Aint RSA_padding_check_PKCS1_OAEP(unsigned char *to, int tlen, 1100SN/A const unsigned char *from, int flen, int num, 1110SN/A const unsigned char *param, int plen) 1120SN/A{ 1130SN/A return RSA_padding_check_PKCS1_OAEP_mgf1(to, tlen, from, flen, num, 1140SN/A param, plen, NULL, NULL); 1150SN/A} 1160SN/A 1170SN/Aint RSA_padding_check_PKCS1_OAEP_mgf1(unsigned char *to, int tlen, 1180SN/A const unsigned char *from, int flen, 1190SN/A int num, const unsigned char *param, 1200SN/A int plen, const EVP_MD *md, 1210SN/A const EVP_MD *mgf1md) 1220SN/A{ 1230SN/A int i, dblen = 0, mlen = -1, one_index = 0, msg_index; 1240SN/A unsigned int good = 0, found_one_byte, mask; 1250SN/A const unsigned char *maskedseed, *maskeddb; 1260SN/A /* 1270SN/A * |em| is the encoded message, zero-padded to exactly |num| bytes: em = 1280SN/A * Y || maskedSeed || maskedDB 1290SN/A */ 1300SN/A unsigned char *db = NULL, *em = NULL, seed[EVP_MAX_MD_SIZE], 1310SN/A phash[EVP_MAX_MD_SIZE]; 1320SN/A int mdlen; 1330SN/A 1340SN/A if (md == NULL) 1350SN/A md = EVP_sha1(); 1360SN/A if (mgf1md == NULL) 1370SN/A mgf1md = md; 1380SN/A 1390SN/A mdlen = EVP_MD_size(md); 1400SN/A 1410SN/A if (tlen <= 0 || flen <= 0) 1420SN/A return -1; 1430SN/A /* 1440SN/A * |num| is the length of the modulus; |flen| is the length of the 1450SN/A * encoded message. Therefore, for any |from| that was obtained by 1460SN/A * decrypting a ciphertext, we must have |flen| <= |num|. Similarly, 1470SN/A * |num| >= 2 * |mdlen| + 2 must hold for the modulus irrespective of 1480SN/A * the ciphertext, see PKCS #1 v2.2, section 7.1.2. 1490SN/A * This does not leak any side-channel information. 1500SN/A */ 1510SN/A if (num < flen || num < 2 * mdlen + 2) { 1520SN/A RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1, 1530SN/A RSA_R_OAEP_DECODING_ERROR); 1540SN/A return -1; 1550SN/A } 1560SN/A 1570SN/A dblen = num - mdlen - 1; 1580SN/A db = OPENSSL_malloc(dblen); 1590SN/A if (db == NULL) { 1600SN/A RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1, ERR_R_MALLOC_FAILURE); 1610SN/A goto cleanup; 1620SN/A } 1630SN/A 1640SN/A em = OPENSSL_malloc(num); 1650SN/A if (em == NULL) { 1660SN/A RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1, 1670SN/A ERR_R_MALLOC_FAILURE); 1680SN/A goto cleanup; 1690SN/A } 1700SN/A 1710SN/A /* 1720SN/A * Caller is encouraged to pass zero-padded message created with 1730SN/A * BN_bn2binpad. Trouble is that since we can't read out of |from|'s 1740SN/A * bounds, it's impossible to have an invariant memory access pattern 1750SN/A * in case |from| was not zero-padded in advance. 1760SN/A */ 1770SN/A for (from += flen, em += num, i = 0; i < num; i++) { 1780SN/A mask = ~constant_time_is_zero(flen); 1790SN/A flen -= 1 & mask; 1800SN/A from -= 1 & mask; 1810SN/A *--em = *from & mask; 1820SN/A } 1830SN/A 1840SN/A /* 1850SN/A * The first byte must be zero, however we must not leak if this is 1860SN/A * true. See James H. Manger, "A Chosen Ciphertext Attack on RSA 1870SN/A * Optimal Asymmetric Encryption Padding (OAEP) [...]", CRYPTO 2001). 1880SN/A */ 1890SN/A good = constant_time_is_zero(em[0]); 1900SN/A 1910SN/A maskedseed = em + 1; 1920SN/A maskeddb = em + 1 + mdlen; 1930SN/A 1940SN/A if (PKCS1_MGF1(seed, mdlen, maskeddb, dblen, mgf1md)) 1950SN/A goto cleanup; 1960SN/A for (i = 0; i < mdlen; i++) 1970SN/A seed[i] ^= maskedseed[i]; 1980SN/A 1990SN/A if (PKCS1_MGF1(db, dblen, seed, mdlen, mgf1md)) 2000SN/A goto cleanup; 2010SN/A for (i = 0; i < dblen; i++) 2020SN/A db[i] ^= maskeddb[i]; 2030SN/A 2040SN/A if (!EVP_Digest((void *)param, plen, phash, NULL, md, NULL)) 2050SN/A goto cleanup; 2060SN/A 2070SN/A good &= constant_time_is_zero(CRYPTO_memcmp(db, phash, mdlen)); 2080SN/A 2090SN/A found_one_byte = 0; 2100SN/A for (i = mdlen; i < dblen; i++) { 2110SN/A /* 2120SN/A * Padding consists of a number of 0-bytes, followed by a 1. 2130SN/A */ 2140SN/A unsigned int equals1 = constant_time_eq(db[i], 1); 2150SN/A unsigned int equals0 = constant_time_is_zero(db[i]); 2160SN/A one_index = constant_time_select_int(~found_one_byte & equals1, 2170SN/A i, one_index); 2180SN/A found_one_byte |= equals1; 2190SN/A good &= (found_one_byte | equals0); 2200SN/A } 2210SN/A 2220SN/A good &= found_one_byte; 2230SN/A 2240SN/A /* 2250SN/A * At this point |good| is zero unless the plaintext was valid, 2260SN/A * so plaintext-awareness ensures timing side-channels are no longer a 2270SN/A * concern. 2280SN/A */ 2290SN/A msg_index = one_index + 1; 2300SN/A mlen = dblen - msg_index; 2310SN/A 2320SN/A /* 2330SN/A * For good measure, do this check in constant time as well. 2340SN/A */ 2350SN/A good &= constant_time_ge(tlen, mlen); 2360SN/A 2370SN/A /* 2380SN/A * Move the result in-place by |dblen|-|mdlen|-1-|mlen| bytes to the left. 2390SN/A * Then if |good| move |mlen| bytes from |db|+|mdlen|+1 to |to|. 2400SN/A * Otherwise leave |to| unchanged. 2410SN/A * Copy the memory back in a way that does not reveal the size of 2420SN/A * the data being copied via a timing side channel. This requires copying 2430SN/A * parts of the buffer multiple times based on the bits set in the real 2440SN/A * length. Clear bits do a non-copy with identical access pattern. 2450SN/A * The loop below has overall complexity of O(N*log(N)). 2460SN/A */ 2470SN/A tlen = constant_time_select_int(constant_time_lt(dblen - mdlen - 1, tlen), 2480SN/A dblen - mdlen - 1, tlen); 2490SN/A for (msg_index = 1; msg_index < dblen - mdlen - 1; msg_index <<= 1) { 2500SN/A mask = ~constant_time_eq(msg_index & (dblen - mdlen - 1 - mlen), 0); 2510SN/A for (i = mdlen + 1; i < dblen - msg_index; i++) 2520SN/A db[i] = constant_time_select_8(mask, db[i + msg_index], db[i]); 2530SN/A } 2540SN/A for (i = 0; i < tlen; i++) { 2550SN/A mask = good & constant_time_lt(i, mlen); 2560SN/A to[i] = constant_time_select_8(mask, db[i + mdlen + 1], to[i]); 2570SN/A } 2580SN/A 2590SN/A /* 2600SN/A * To avoid chosen ciphertext attacks, the error message should not 2610SN/A * reveal which kind of decoding error happened. 2620SN/A */ 2630SN/A RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1, 2640SN/A RSA_R_OAEP_DECODING_ERROR); 2650SN/A err_clear_last_constant_time(1 & good); 2660SN/A cleanup: 2670SN/A OPENSSL_cleanse(seed, sizeof(seed)); 2680SN/A OPENSSL_cleanse(db, dblen); 2690SN/A OPENSSL_free(db); 2700SN/A OPENSSL_cleanse(em, num); 2710SN/A OPENSSL_free(em); 2720SN/A 2730SN/A return constant_time_select_int(good, mlen, -1); 2740SN/A} 2750SN/A 2760SN/Aint PKCS1_MGF1(unsigned char *mask, long len, 2770SN/A const unsigned char *seed, long seedlen, const EVP_MD *dgst) 2780SN/A{ 2790SN/A long i, outlen = 0; 2800SN/A unsigned char cnt[4]; 2810SN/A EVP_MD_CTX c; 2820SN/A unsigned char md[EVP_MAX_MD_SIZE]; 2830SN/A int mdlen; 2840SN/A int rv = -1; 2850SN/A 2860SN/A EVP_MD_CTX_init(&c); 2870SN/A mdlen = EVP_MD_size(dgst); 2880SN/A if (mdlen < 0) 2890SN/A goto err; 2900SN/A for (i = 0; outlen < len; i++) { 2910SN/A cnt[0] = (unsigned char)((i >> 24) & 255); 2920SN/A cnt[1] = (unsigned char)((i >> 16) & 255); 2930SN/A cnt[2] = (unsigned char)((i >> 8)) & 255; 2940SN/A cnt[3] = (unsigned char)(i & 255); 2950SN/A if (!EVP_DigestInit_ex(&c, dgst, NULL) 2960SN/A || !EVP_DigestUpdate(&c, seed, seedlen) 2970SN/A || !EVP_DigestUpdate(&c, cnt, 4)) 2980SN/A goto err; 2990SN/A if (outlen + mdlen <= len) { 3000SN/A if (!EVP_DigestFinal_ex(&c, mask + outlen, NULL)) 3010SN/A goto err; 3020SN/A outlen += mdlen; 3030SN/A } else { 3040SN/A if (!EVP_DigestFinal_ex(&c, md, NULL)) 3050SN/A goto err; 3060SN/A memcpy(mask + outlen, md, len - outlen); 3070SN/A outlen = len; 3080SN/A } 3090SN/A } 3100SN/A rv = 0; 3110SN/A err: 3120SN/A EVP_MD_CTX_cleanup(&c); 3130SN/A return rv; 3140SN/A} 3150SN/A 3160SN/A#endif 3170SN/A