1/* 2 * Copyright 1999-2021 The OpenSSL Project Authors. All Rights Reserved. 3 * 4 * Licensed under the Apache License 2.0 (the "License"). You may not use 5 * this file except in compliance with the License. You can obtain a copy 6 * in the file LICENSE in the source distribution or at 7 * https://www.openssl.org/source/license.html 8 */ 9 10/* EME-OAEP as defined in RFC 2437 (PKCS #1 v2.0) */ 11 12/* 13 * See Victor Shoup, "OAEP reconsidered," Nov. 2000, <URL: 14 * http://www.shoup.net/papers/oaep.ps.Z> for problems with the security 15 * proof for the original OAEP scheme, which EME-OAEP is based on. A new 16 * proof can be found in E. Fujisaki, T. Okamoto, D. Pointcheval, J. Stern, 17 * "RSA-OEAP is Still Alive!", Dec. 2000, <URL: 18 * http://eprint.iacr.org/2000/061/>. The new proof has stronger requirements 19 * for the underlying permutation: "partial-one-wayness" instead of 20 * one-wayness. For the RSA function, this is an equivalent notion. 21 */ 22 23/* 24 * RSA low level APIs are deprecated for public use, but still ok for 25 * internal use. 26 */ 27#include "internal/deprecated.h" 28 29#include "internal/constant_time.h" 30 31#include <stdio.h> 32#include "internal/cryptlib.h" 33#include <openssl/bn.h> 34#include <openssl/evp.h> 35#include <openssl/rand.h> 36#include <openssl/sha.h> 37#include "rsa_local.h" 38 39int RSA_padding_add_PKCS1_OAEP(unsigned char *to, int tlen, 40 const unsigned char *from, int flen, 41 const unsigned char *param, int plen) 42{ 43 return ossl_rsa_padding_add_PKCS1_OAEP_mgf1_ex(NULL, to, tlen, from, flen, 44 param, plen, NULL, NULL); 45} 46 47/* 48 * Perform the padding as per NIST 800-56B 7.2.2.3 49 * from (K) is the key material. 50 * param (A) is the additional input. 51 * Step numbers are included here but not in the constant time inverse below 52 * to avoid complicating an already difficult enough function. 53 */ 54int ossl_rsa_padding_add_PKCS1_OAEP_mgf1_ex(OSSL_LIB_CTX *libctx, 55 unsigned char *to, int tlen, 56 const unsigned char *from, int flen, 57 const unsigned char *param, 58 int plen, const EVP_MD *md, 59 const EVP_MD *mgf1md) 60{ 61 int rv = 0; 62 int i, emlen = tlen - 1; 63 unsigned char *db, *seed; 64 unsigned char *dbmask = NULL; 65 unsigned char seedmask[EVP_MAX_MD_SIZE]; 66 int mdlen, dbmask_len = 0; 67 68 if (md == NULL) { 69#ifndef FIPS_MODULE 70 md = EVP_sha1(); 71#else 72 ERR_raise(ERR_LIB_RSA, ERR_R_PASSED_NULL_PARAMETER); 73 return 0; 74#endif 75 } 76 if (mgf1md == NULL) 77 mgf1md = md; 78 79 mdlen = EVP_MD_get_size(md); 80 if (mdlen <= 0) { 81 ERR_raise(ERR_LIB_RSA, RSA_R_INVALID_LENGTH); 82 return 0; 83 } 84 85 /* step 2b: check KLen > nLen - 2 HLen - 2 */ 86 if (flen > emlen - 2 * mdlen - 1) { 87 ERR_raise(ERR_LIB_RSA, RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE); 88 return 0; 89 } 90 91 if (emlen < 2 * mdlen + 1) { 92 ERR_raise(ERR_LIB_RSA, RSA_R_KEY_SIZE_TOO_SMALL); 93 return 0; 94 } 95 96 /* step 3i: EM = 00000000 || maskedMGF || maskedDB */ 97 to[0] = 0; 98 seed = to + 1; 99 db = to + mdlen + 1; 100 101 /* step 3a: hash the additional input */ 102 if (!EVP_Digest((void *)param, plen, db, NULL, md, NULL)) 103 goto err; 104 /* step 3b: zero bytes array of length nLen - KLen - 2 HLen -2 */ 105 memset(db + mdlen, 0, emlen - flen - 2 * mdlen - 1); 106 /* step 3c: DB = HA || PS || 00000001 || K */ 107 db[emlen - flen - mdlen - 1] = 0x01; 108 memcpy(db + emlen - flen - mdlen, from, (unsigned int)flen); 109 /* step 3d: generate random byte string */ 110 if (RAND_bytes_ex(libctx, seed, mdlen, 0) <= 0) 111 goto err; 112 113 dbmask_len = emlen - mdlen; 114 dbmask = OPENSSL_malloc(dbmask_len); 115 if (dbmask == NULL) { 116 ERR_raise(ERR_LIB_RSA, ERR_R_MALLOC_FAILURE); 117 goto err; 118 } 119 120 /* step 3e: dbMask = MGF(mgfSeed, nLen - HLen - 1) */ 121 if (PKCS1_MGF1(dbmask, dbmask_len, seed, mdlen, mgf1md) < 0) 122 goto err; 123 /* step 3f: maskedDB = DB XOR dbMask */ 124 for (i = 0; i < dbmask_len; i++) 125 db[i] ^= dbmask[i]; 126 127 /* step 3g: mgfSeed = MGF(maskedDB, HLen) */ 128 if (PKCS1_MGF1(seedmask, mdlen, db, dbmask_len, mgf1md) < 0) 129 goto err; 130 /* stepo 3h: maskedMGFSeed = mgfSeed XOR mgfSeedMask */ 131 for (i = 0; i < mdlen; i++) 132 seed[i] ^= seedmask[i]; 133 rv = 1; 134 135 err: 136 OPENSSL_cleanse(seedmask, sizeof(seedmask)); 137 OPENSSL_clear_free(dbmask, dbmask_len); 138 return rv; 139} 140 141int RSA_padding_add_PKCS1_OAEP_mgf1(unsigned char *to, int tlen, 142 const unsigned char *from, int flen, 143 const unsigned char *param, int plen, 144 const EVP_MD *md, const EVP_MD *mgf1md) 145{ 146 return ossl_rsa_padding_add_PKCS1_OAEP_mgf1_ex(NULL, to, tlen, from, flen, 147 param, plen, md, mgf1md); 148} 149 150int RSA_padding_check_PKCS1_OAEP(unsigned char *to, int tlen, 151 const unsigned char *from, int flen, int num, 152 const unsigned char *param, int plen) 153{ 154 return RSA_padding_check_PKCS1_OAEP_mgf1(to, tlen, from, flen, num, 155 param, plen, NULL, NULL); 156} 157 158int RSA_padding_check_PKCS1_OAEP_mgf1(unsigned char *to, int tlen, 159 const unsigned char *from, int flen, 160 int num, const unsigned char *param, 161 int plen, const EVP_MD *md, 162 const EVP_MD *mgf1md) 163{ 164 int i, dblen = 0, mlen = -1, one_index = 0, msg_index; 165 unsigned int good = 0, found_one_byte, mask; 166 const unsigned char *maskedseed, *maskeddb; 167 /* 168 * |em| is the encoded message, zero-padded to exactly |num| bytes: em = 169 * Y || maskedSeed || maskedDB 170 */ 171 unsigned char *db = NULL, *em = NULL, seed[EVP_MAX_MD_SIZE], 172 phash[EVP_MAX_MD_SIZE]; 173 int mdlen; 174 175 if (md == NULL) { 176#ifndef FIPS_MODULE 177 md = EVP_sha1(); 178#else 179 ERR_raise(ERR_LIB_RSA, ERR_R_PASSED_NULL_PARAMETER); 180 return -1; 181#endif 182 } 183 184 if (mgf1md == NULL) 185 mgf1md = md; 186 187 mdlen = EVP_MD_get_size(md); 188 189 if (tlen <= 0 || flen <= 0) 190 return -1; 191 /* 192 * |num| is the length of the modulus; |flen| is the length of the 193 * encoded message. Therefore, for any |from| that was obtained by 194 * decrypting a ciphertext, we must have |flen| <= |num|. Similarly, 195 * |num| >= 2 * |mdlen| + 2 must hold for the modulus irrespective of 196 * the ciphertext, see PKCS #1 v2.2, section 7.1.2. 197 * This does not leak any side-channel information. 198 */ 199 if (num < flen || num < 2 * mdlen + 2) { 200 ERR_raise(ERR_LIB_RSA, RSA_R_OAEP_DECODING_ERROR); 201 return -1; 202 } 203 204 dblen = num - mdlen - 1; 205 db = OPENSSL_malloc(dblen); 206 if (db == NULL) { 207 ERR_raise(ERR_LIB_RSA, ERR_R_MALLOC_FAILURE); 208 goto cleanup; 209 } 210 211 em = OPENSSL_malloc(num); 212 if (em == NULL) { 213 ERR_raise(ERR_LIB_RSA, ERR_R_MALLOC_FAILURE); 214 goto cleanup; 215 } 216 217 /* 218 * Caller is encouraged to pass zero-padded message created with 219 * BN_bn2binpad. Trouble is that since we can't read out of |from|'s 220 * bounds, it's impossible to have an invariant memory access pattern 221 * in case |from| was not zero-padded in advance. 222 */ 223 for (from += flen, em += num, i = 0; i < num; i++) { 224 mask = ~constant_time_is_zero(flen); 225 flen -= 1 & mask; 226 from -= 1 & mask; 227 *--em = *from & mask; 228 } 229 230 /* 231 * The first byte must be zero, however we must not leak if this is 232 * true. See James H. Manger, "A Chosen Ciphertext Attack on RSA 233 * Optimal Asymmetric Encryption Padding (OAEP) [...]", CRYPTO 2001). 234 */ 235 good = constant_time_is_zero(em[0]); 236 237 maskedseed = em + 1; 238 maskeddb = em + 1 + mdlen; 239 240 if (PKCS1_MGF1(seed, mdlen, maskeddb, dblen, mgf1md)) 241 goto cleanup; 242 for (i = 0; i < mdlen; i++) 243 seed[i] ^= maskedseed[i]; 244 245 if (PKCS1_MGF1(db, dblen, seed, mdlen, mgf1md)) 246 goto cleanup; 247 for (i = 0; i < dblen; i++) 248 db[i] ^= maskeddb[i]; 249 250 if (!EVP_Digest((void *)param, plen, phash, NULL, md, NULL)) 251 goto cleanup; 252 253 good &= constant_time_is_zero(CRYPTO_memcmp(db, phash, mdlen)); 254 255 found_one_byte = 0; 256 for (i = mdlen; i < dblen; i++) { 257 /* 258 * Padding consists of a number of 0-bytes, followed by a 1. 259 */ 260 unsigned int equals1 = constant_time_eq(db[i], 1); 261 unsigned int equals0 = constant_time_is_zero(db[i]); 262 one_index = constant_time_select_int(~found_one_byte & equals1, 263 i, one_index); 264 found_one_byte |= equals1; 265 good &= (found_one_byte | equals0); 266 } 267 268 good &= found_one_byte; 269 270 /* 271 * At this point |good| is zero unless the plaintext was valid, 272 * so plaintext-awareness ensures timing side-channels are no longer a 273 * concern. 274 */ 275 msg_index = one_index + 1; 276 mlen = dblen - msg_index; 277 278 /* 279 * For good measure, do this check in constant time as well. 280 */ 281 good &= constant_time_ge(tlen, mlen); 282 283 /* 284 * Move the result in-place by |dblen|-|mdlen|-1-|mlen| bytes to the left. 285 * Then if |good| move |mlen| bytes from |db|+|mdlen|+1 to |to|. 286 * Otherwise leave |to| unchanged. 287 * Copy the memory back in a way that does not reveal the size of 288 * the data being copied via a timing side channel. This requires copying 289 * parts of the buffer multiple times based on the bits set in the real 290 * length. Clear bits do a non-copy with identical access pattern. 291 * The loop below has overall complexity of O(N*log(N)). 292 */ 293 tlen = constant_time_select_int(constant_time_lt(dblen - mdlen - 1, tlen), 294 dblen - mdlen - 1, tlen); 295 for (msg_index = 1; msg_index < dblen - mdlen - 1; msg_index <<= 1) { 296 mask = ~constant_time_eq(msg_index & (dblen - mdlen - 1 - mlen), 0); 297 for (i = mdlen + 1; i < dblen - msg_index; i++) 298 db[i] = constant_time_select_8(mask, db[i + msg_index], db[i]); 299 } 300 for (i = 0; i < tlen; i++) { 301 mask = good & constant_time_lt(i, mlen); 302 to[i] = constant_time_select_8(mask, db[i + mdlen + 1], to[i]); 303 } 304 305#ifndef FIPS_MODULE 306 /* 307 * To avoid chosen ciphertext attacks, the error message should not 308 * reveal which kind of decoding error happened. 309 * 310 * This trick doesn't work in the FIPS provider because libcrypto manages 311 * the error stack. Instead we opt not to put an error on the stack at all 312 * in case of padding failure in the FIPS provider. 313 */ 314 ERR_raise(ERR_LIB_RSA, RSA_R_OAEP_DECODING_ERROR); 315 err_clear_last_constant_time(1 & good); 316#endif 317 cleanup: 318 OPENSSL_cleanse(seed, sizeof(seed)); 319 OPENSSL_clear_free(db, dblen); 320 OPENSSL_clear_free(em, num); 321 322 return constant_time_select_int(good, mlen, -1); 323} 324 325/* 326 * Mask Generation Function corresponding to section 7.2.2.2 of NIST SP 800-56B. 327 * The variables are named differently to NIST: 328 * mask (T) and len (maskLen)are the returned mask. 329 * seed (mgfSeed). 330 * The range checking steps inm the process are performed outside. 331 */ 332int PKCS1_MGF1(unsigned char *mask, long len, 333 const unsigned char *seed, long seedlen, const EVP_MD *dgst) 334{ 335 long i, outlen = 0; 336 unsigned char cnt[4]; 337 EVP_MD_CTX *c = EVP_MD_CTX_new(); 338 unsigned char md[EVP_MAX_MD_SIZE]; 339 int mdlen; 340 int rv = -1; 341 342 if (c == NULL) 343 goto err; 344 mdlen = EVP_MD_get_size(dgst); 345 if (mdlen < 0) 346 goto err; 347 /* step 4 */ 348 for (i = 0; outlen < len; i++) { 349 /* step 4a: D = I2BS(counter, 4) */ 350 cnt[0] = (unsigned char)((i >> 24) & 255); 351 cnt[1] = (unsigned char)((i >> 16) & 255); 352 cnt[2] = (unsigned char)((i >> 8)) & 255; 353 cnt[3] = (unsigned char)(i & 255); 354 /* step 4b: T =T || hash(mgfSeed || D) */ 355 if (!EVP_DigestInit_ex(c, dgst, NULL) 356 || !EVP_DigestUpdate(c, seed, seedlen) 357 || !EVP_DigestUpdate(c, cnt, 4)) 358 goto err; 359 if (outlen + mdlen <= len) { 360 if (!EVP_DigestFinal_ex(c, mask + outlen, NULL)) 361 goto err; 362 outlen += mdlen; 363 } else { 364 if (!EVP_DigestFinal_ex(c, md, NULL)) 365 goto err; 366 memcpy(mask + outlen, md, len - outlen); 367 outlen = len; 368 } 369 } 370 rv = 0; 371 err: 372 OPENSSL_cleanse(md, sizeof(md)); 373 EVP_MD_CTX_free(c); 374 return rv; 375} 376