/*
* Copyright 1999-2019 The OpenSSL Project Authors. All Rights Reserved.
*
* Licensed under the OpenSSL license (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, <URL:
* http://www.shoup.net/papers/oaep.ps.Z> 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, <URL:
* http://eprint.iacr.org/2000/061/>. 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 "internal/constant_time.h"
#include <stdio.h>
#include "internal/cryptlib.h"
#include <openssl/bn.h>
#include <openssl/evp.h>
#include <openssl/rand.h>
#include <openssl/sha.h>
#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 RSA_padding_add_PKCS1_OAEP_mgf1(to, tlen, from, flen,
param, plen, NULL, NULL);
}
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)
{
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)
md = EVP_sha1();
if (mgf1md == NULL)
mgf1md = md;
mdlen = EVP_MD_size(md);
if (flen > emlen - 2 * mdlen - 1) {
RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP_MGF1,
RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE);
return 0;
}
if (emlen < 2 * mdlen + 1) {
RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP_MGF1,
RSA_R_KEY_SIZE_TOO_SMALL);
return 0;
}
to[0] = 0;
seed = to + 1;
db = to + mdlen + 1;
if (!EVP_Digest((void *)param, plen, db, NULL, md, NULL))
goto err;
memset(db + mdlen, 0, emlen - flen - 2 * mdlen - 1);
db[emlen - flen - mdlen - 1] = 0x01;
memcpy(db + emlen - flen - mdlen, from, (unsigned int)flen);
if (RAND_bytes(seed, mdlen) <= 0)
goto err;
dbmask_len = emlen - mdlen;
dbmask = OPENSSL_malloc(dbmask_len);
if (dbmask == NULL) {
RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP_MGF1, ERR_R_MALLOC_FAILURE);
goto err;
}
if (PKCS1_MGF1(dbmask, dbmask_len, seed, mdlen, mgf1md) < 0)
goto err;
for (i = 0; i < dbmask_len; i++)
db[i] ^= dbmask[i];
if (PKCS1_MGF1(seedmask, mdlen, db, dbmask_len, mgf1md) < 0)
goto err;
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_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)
md = EVP_sha1();
if (mgf1md == NULL)
mgf1md = md;
mdlen = EVP_MD_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) {
RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1,
RSA_R_OAEP_DECODING_ERROR);
return -1;
}
dblen = num - mdlen - 1;
db = OPENSSL_malloc(dblen);
if (db == NULL) {
RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1, ERR_R_MALLOC_FAILURE);
goto cleanup;
}
em = OPENSSL_malloc(num);
if (em == NULL) {
RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1,
ERR_R_MALLOC_FAILURE);
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]);
}
/*
* 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_MGF1,
RSA_R_OAEP_DECODING_ERROR);
err_clear_last_constant_time(1 & good);
cleanup:
OPENSSL_cleanse(seed, sizeof(seed));
OPENSSL_clear_free(db, dblen);
OPENSSL_clear_free(em, num);
return constant_time_select_int(good, mlen, -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 = EVP_MD_CTX_new();
unsigned char md[EVP_MAX_MD_SIZE];
int mdlen;
int rv = -1;
if (c == NULL)
goto err;
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:
OPENSSL_cleanse(md, sizeof(md));
EVP_MD_CTX_free(c);
return rv;
}