/* 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>

EXPORT_C int MGF1(unsigned char *mask, long len,

	const unsigned char *seed, long seedlen);

EXPORT_C 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;

	}

EXPORT_C 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_CHECK_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;

	}

EXPORT_C 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;

	EVP_MD_CTX_init(&c);

	mdlen = EVP_MD_size(dgst);

	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,dgst, NULL);

		EVP_DigestUpdate(&c, seed, seedlen);

		EVP_DigestUpdate(&c, cnt, 4);

		if (outlen + mdlen <= len)

			{

			EVP_DigestFinal_ex(&c, mask + outlen, NULL);

			outlen += mdlen;

			}

		else

			{

			EVP_DigestFinal_ex(&c, md, NULL);

			memcpy(mask + outlen, md, len - outlen);

			outlen = len;

			}

		}

	EVP_MD_CTX_cleanup(&c);

	return 0;

	}

EXPORT_C int MGF1(unsigned char *mask, long len, const unsigned char *seed, long seedlen)

	{

	return PKCS1_MGF1(mask, len, seed, seedlen, EVP_sha1());

	}

#endif