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/* $OpenBSD: rsa_oaep.c,v 1.29 2018/08/19 20:17:20 tb Exp $ */
/* Written by Ulf Moeller. This software is distributed on an "AS IS"
basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. */
/* 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 <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <openssl/opensslconf.h>
#if !defined(OPENSSL_NO_SHA) && !defined(OPENSSL_NO_SHA1)
#include <openssl/bn.h>
#include <openssl/err.h>
#include <openssl/evp.h>
#include <openssl/rsa.h>
#include <openssl/sha.h>
static int MGF1(unsigned char *mask, long len, const unsigned char *seed,
long seedlen);
int
RSA_padding_add_PKCS1_OAEP(unsigned char *to, int tlen,
const unsigned char *from, int flen, const unsigned char *param, int plen)
{
int i, emlen = tlen - 1;
unsigned char *db, *seed;
unsigned char *dbmask, seedmask[SHA_DIGEST_LENGTH];
if (flen > emlen - 2 * SHA_DIGEST_LENGTH - 1) {
RSAerror(RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE);
return 0;
}
if (emlen < 2 * SHA_DIGEST_LENGTH + 1) {
RSAerror(RSA_R_KEY_SIZE_TOO_SMALL);
return 0;
}
to[0] = 0;
seed = to + 1;
db = to + SHA_DIGEST_LENGTH + 1;
if (!EVP_Digest((void *)param, plen, db, NULL, EVP_sha1(), NULL))
return 0;
memset(db + SHA_DIGEST_LENGTH, 0,
emlen - flen - 2 * SHA_DIGEST_LENGTH - 1);
db[emlen - flen - SHA_DIGEST_LENGTH - 1] = 0x01;
memcpy(db + emlen - flen - SHA_DIGEST_LENGTH, from, flen);
arc4random_buf(seed, SHA_DIGEST_LENGTH);
dbmask = malloc(emlen - SHA_DIGEST_LENGTH);
if (dbmask == NULL) {
RSAerror(ERR_R_MALLOC_FAILURE);
return 0;
}
if (MGF1(dbmask, emlen - SHA_DIGEST_LENGTH, seed,
SHA_DIGEST_LENGTH) < 0) {
free(dbmask);
return 0;
}
for (i = 0; i < emlen - SHA_DIGEST_LENGTH; i++)
db[i] ^= dbmask[i];
if (MGF1(seedmask, SHA_DIGEST_LENGTH, db,
emlen - SHA_DIGEST_LENGTH) < 0) {
free(dbmask);
return 0;
}
for (i = 0; i < SHA_DIGEST_LENGTH; i++)
seed[i] ^= seedmask[i];
free(dbmask);
return 1;
}
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)
{
int i, dblen, mlen = -1;
const unsigned char *maskeddb;
int lzero;
unsigned char *db = NULL;
unsigned char seed[SHA_DIGEST_LENGTH], phash[SHA_DIGEST_LENGTH];
unsigned char *padded_from;
int bad = 0;
if (--num < 2 * SHA_DIGEST_LENGTH + 1)
/*
* 'num' is the length of the modulus, i.e. does not depend
* on the particular ciphertext.
*/
goto decoding_err;
lzero = num - flen;
if (lzero < 0) {
/*
* signalling this error immediately after detection might allow
* for side-channel attacks (e.g. timing if 'plen' is huge
* -- cf. James H. Manger, "A Chosen Ciphertext Attack on RSA
* Optimal Asymmetric Encryption Padding (OAEP) [...]",
* CRYPTO 2001), so we use a 'bad' flag
*/
bad = 1;
lzero = 0;
flen = num; /* don't overflow the memcpy to padded_from */
}
dblen = num - SHA_DIGEST_LENGTH;
if ((db = malloc(dblen + num)) == NULL) {
RSAerror(ERR_R_MALLOC_FAILURE);
return -1;
}
/*
* Always do this zero-padding copy (even when lzero == 0)
* to avoid leaking timing info about the value of lzero.
*/
padded_from = db + dblen;
memset(padded_from, 0, lzero);
memcpy(padded_from + lzero, from, flen);
maskeddb = padded_from + SHA_DIGEST_LENGTH;
if (MGF1(seed, SHA_DIGEST_LENGTH, maskeddb, dblen))
goto err;
for (i = 0; i < SHA_DIGEST_LENGTH; i++)
seed[i] ^= padded_from[i];
if (MGF1(db, dblen, seed, SHA_DIGEST_LENGTH))
goto err;
for (i = 0; i < dblen; i++)
db[i] ^= maskeddb[i];
if (!EVP_Digest((void *)param, plen, phash, NULL, EVP_sha1(), NULL))
goto err;
if (timingsafe_memcmp(db, phash, SHA_DIGEST_LENGTH) != 0 || bad)
goto decoding_err;
else {
for (i = SHA_DIGEST_LENGTH; i < dblen; i++)
if (db[i] != 0x00)
break;
if (i == dblen || db[i] != 0x01)
goto decoding_err;
else {
/* everything looks OK */
mlen = dblen - ++i;
if (tlen < mlen) {
RSAerror(RSA_R_DATA_TOO_LARGE);
mlen = -1;
} else
memcpy(to, db + i, mlen);
}
}
free(db);
return mlen;
decoding_err:
/*
* To avoid chosen ciphertext attacks, the error message should not
* reveal which kind of decoding error happened
*/
RSAerror(RSA_R_OAEP_DECODING_ERROR);
err:
free(db);
return -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;
unsigned char md[EVP_MAX_MD_SIZE];
int mdlen;
int rv = -1;
EVP_MD_CTX_init(&c);
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:
EVP_MD_CTX_cleanup(&c);
return rv;
}
static int
MGF1(unsigned char *mask, long len, const unsigned char *seed, long seedlen)
{
return PKCS1_MGF1(mask, len, seed, seedlen, EVP_sha1());
}
#endif
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