rsa_oaep.c   [plain text]

/* crypto/rsa/rsa_oaep.c */
/* 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.
 */


#if !defined(OPENSSL_NO_SHA) && !defined(OPENSSL_NO_SHA1)
#include <stdio.h>
#include "cryptlib.h"
#include <openssl/bn.h>
#include <openssl/rsa.h>
#include <openssl/evp.h>
#include <openssl/rand.h>
#include <openssl/sha.h>

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)
		{
		RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP,
		   RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE);
		return 0;
		}

	if (emlen < 2 * SHA_DIGEST_LENGTH + 1)
		{
		RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP, RSA_R_KEY_SIZE_TOO_SMALL);
		return 0;
		}

	dbmask = OPENSSL_malloc(emlen - SHA_DIGEST_LENGTH);
	if (dbmask == NULL)
		{
		RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP, ERR_R_MALLOC_FAILURE);
		return 0;
		}

	to[0] = 0;
	seed = to + 1;
	db = to + SHA_DIGEST_LENGTH + 1;

	EVP_Digest((void *)param, plen, db, NULL, EVP_sha1(), NULL);
	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, (unsigned int) flen);
	if (RAND_bytes(seed, SHA_DIGEST_LENGTH) <= 0)
		return 0;
#ifdef PKCS_TESTVECT
	memcpy(seed,
	   "\xaa\xfd\x12\xf6\x59\xca\xe6\x34\x89\xb4\x79\xe5\x07\x6d\xde\xc2\xf0\x6c\xb5\x8f",
	   20);
#endif

	MGF1(dbmask, emlen - SHA_DIGEST_LENGTH, seed, SHA_DIGEST_LENGTH);
	for (i = 0; i < emlen - SHA_DIGEST_LENGTH; i++)
		db[i] ^= dbmask[i];

	MGF1(seedmask, SHA_DIGEST_LENGTH, db, emlen - SHA_DIGEST_LENGTH);
	for (i = 0; i < SHA_DIGEST_LENGTH; i++)
		seed[i] ^= seedmask[i];

	OPENSSL_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, seed[SHA_DIGEST_LENGTH], phash[SHA_DIGEST_LENGTH];
	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)
		{
		/* lzero == -1 */

		/* 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;
		}
	maskeddb = from - lzero + SHA_DIGEST_LENGTH;

	dblen = num - SHA_DIGEST_LENGTH;
	db = OPENSSL_malloc(dblen);
	if (db == NULL)
		{
		RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP, ERR_R_MALLOC_FAILURE);
		return -1;
		}

	MGF1(seed, SHA_DIGEST_LENGTH, maskeddb, dblen);
	for (i = lzero; i < SHA_DIGEST_LENGTH; i++)
		seed[i] ^= from[i - lzero];
  
	MGF1(db, dblen, seed, SHA_DIGEST_LENGTH);
	for (i = 0; i < dblen; i++)
		db[i] ^= maskeddb[i];

	EVP_Digest((void *)param, plen, phash, NULL, EVP_sha1(), NULL);

	if (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 (db[i] != 0x01 || i++ >= dblen)
			goto decoding_err;
		else
			{
			/* everything looks OK */

			mlen = dblen - i;
			if (tlen < mlen)
				{
				RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP, RSA_R_DATA_TOO_LARGE);
				mlen = -1;
				}
			else
				memcpy(to, db + i, mlen);
			}
		}
	OPENSSL_free(db);
	return mlen;

decoding_err:
	/* 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, RSA_R_OAEP_DECODING_ERROR);
	if (db != NULL) OPENSSL_free(db);
	return -1;
	}

int MGF1(unsigned char *mask, long len,
	const unsigned char *seed, long seedlen)
	{
	long i, outlen = 0;
	unsigned char cnt[4];
	EVP_MD_CTX c;
	unsigned char md[SHA_DIGEST_LENGTH];

	EVP_MD_CTX_init(&c);
	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);
		EVP_DigestInit_ex(&c,EVP_sha1(), NULL);
		EVP_DigestUpdate(&c, seed, seedlen);
		EVP_DigestUpdate(&c, cnt, 4);
		if (outlen + SHA_DIGEST_LENGTH <= len)
			{
			EVP_DigestFinal_ex(&c, mask + outlen, NULL);
			outlen += SHA_DIGEST_LENGTH;
			}
		else
			{
			EVP_DigestFinal_ex(&c, md, NULL);
			memcpy(mask + outlen, md, len - outlen);
			outlen = len;
			}
		}
	EVP_MD_CTX_cleanup(&c);
	return 0;
	}
#endif