text: /* $OpenBSD: rsa_pss.c,v 1.8 2014/07/10 13:58:23 jsing Exp $ */
  /* Written by Dr Stephen N Henson (steve@openssl.org) for the OpenSSL
   * project 2005.
   */
  /* ====================================================================
   * Copyright (c) 2005 The OpenSSL Project.  All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   *
   * 1. Redistributions of source code must retain the above copyright
   *    notice, this list of conditions and the following disclaimer.
   *
   * 2. Redistributions in binary form must reproduce the above copyright
   *    notice, this list of conditions and the following disclaimer in
   *    the documentation and/or other materials provided with the
   *    distribution.
   *
   * 3. All advertising materials mentioning features or use of this
   *    software must display the following acknowledgment:
   *    "This product includes software developed by the OpenSSL Project
   *    for use in the OpenSSL Toolkit. (http://www.OpenSSL.org/)"
   *
   * 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to
   *    endorse or promote products derived from this software without
   *    prior written permission. For written permission, please contact
   *    licensing@OpenSSL.org.
   *
   * 5. Products derived from this software may not be called "OpenSSL"
   *    nor may "OpenSSL" appear in their names without prior written
   *    permission of the OpenSSL Project.
   *
   * 6. Redistributions of any form whatsoever must retain the following
   *    acknowledgment:
   *    "This product includes software developed by the OpenSSL Project
   *    for use in the OpenSSL Toolkit (http://www.OpenSSL.org/)"
   *
   * THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY
   * EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
   * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE OpenSSL PROJECT OR
   * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
   * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
   * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
   * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
   * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
   * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
   * OF THE POSSIBILITY OF SUCH DAMAGE.
   * ====================================================================
   *
   * This product includes cryptographic software written by Eric Young
   * (eay@cryptsoft.com).  This product includes software written by Tim
   * Hudson (tjh@cryptsoft.com).
   *
   */
  
  #include <stdio.h>
  #include <string.h>
  
  #include <openssl/bn.h>
  #include <openssl/err.h>
  #include <openssl/evp.h>
  #include <openssl/rand.h>
  #include <openssl/rsa.h>
  #include <openssl/sha.h>
  
  static const unsigned char zeroes[] = { 0, 0, 0, 0, 0, 0, 0, 0 };
  
  int
  RSA_verify_PKCS1_PSS(RSA *rsa, const unsigned char *mHash, const EVP_MD *Hash,
      const unsigned char *EM, int sLen)
  {
  	return RSA_verify_PKCS1_PSS_mgf1(rsa, mHash, Hash, NULL, EM, sLen);
  }
  
  int
  RSA_verify_PKCS1_PSS_mgf1(RSA *rsa, const unsigned char *mHash,
      const EVP_MD *Hash, const EVP_MD *mgf1Hash, const unsigned char *EM,
      int sLen)
  {
  	int i;
  	int ret = 0;
  	int hLen, maskedDBLen, MSBits, emLen;
  	const unsigned char *H;
  	unsigned char *DB = NULL;
  	EVP_MD_CTX ctx;
  	unsigned char H_[EVP_MAX_MD_SIZE];
  
  	EVP_MD_CTX_init(&ctx);
  
  	if (mgf1Hash == NULL)
  		mgf1Hash = Hash;
  
  	hLen = EVP_MD_size(Hash);
  	if (hLen < 0)
  		goto err;
  	/*
  	 * Negative sLen has special meanings:
  	 *	-1	sLen == hLen
  	 *	-2	salt length is autorecovered from signature
  	 *	-N	reserved
  	 */
  	if (sLen == -1)
  		sLen = hLen;
  	else if (sLen == -2)
  		sLen = -2;
  	else if (sLen < -2) {
  		RSAerr(RSA_F_RSA_VERIFY_PKCS1_PSS_MGF1,
  		    RSA_R_SLEN_CHECK_FAILED);
  		goto err;
  	}
  
  	MSBits = (BN_num_bits(rsa->n) - 1) & 0x7;
  	emLen = RSA_size(rsa);
  	if (EM[0] & (0xFF << MSBits)) {
  		RSAerr(RSA_F_RSA_VERIFY_PKCS1_PSS_MGF1,
  		    RSA_R_FIRST_OCTET_INVALID);
  		goto err;
  	}
  	if (MSBits == 0) {
  		EM++;
  		emLen--;
  	}
  	if (emLen < (hLen + sLen + 2)) {
  		/* sLen can be small negative */
  		RSAerr(RSA_F_RSA_VERIFY_PKCS1_PSS_MGF1, RSA_R_DATA_TOO_LARGE);
  		goto err;
  	}
  	if (EM[emLen - 1] != 0xbc) {
  		RSAerr(RSA_F_RSA_VERIFY_PKCS1_PSS_MGF1,
  		    RSA_R_LAST_OCTET_INVALID);
  		goto err;
  	}
  	maskedDBLen = emLen - hLen - 1;
  	H = EM + maskedDBLen;
  	DB = malloc(maskedDBLen);
  	if (!DB) {
  		RSAerr(RSA_F_RSA_VERIFY_PKCS1_PSS_MGF1, ERR_R_MALLOC_FAILURE);
  		goto err;
  	}
  	if (PKCS1_MGF1(DB, maskedDBLen, H, hLen, mgf1Hash) < 0)
  		goto err;
  	for (i = 0; i < maskedDBLen; i++)
  		DB[i] ^= EM[i];
  	if (MSBits)
  		DB[0] &= 0xFF >> (8 - MSBits);
  	for (i = 0; DB[i] == 0 && i < (maskedDBLen - 1); i++)
  		;
  	if (DB[i++] != 0x1) {
  		RSAerr(RSA_F_RSA_VERIFY_PKCS1_PSS_MGF1,
  		    RSA_R_SLEN_RECOVERY_FAILED);
  		goto err;
  	}
  	if (sLen >= 0 && (maskedDBLen - i) != sLen) {
  		RSAerr(RSA_F_RSA_VERIFY_PKCS1_PSS_MGF1,
  		    RSA_R_SLEN_CHECK_FAILED);
  		goto err;
  	}
  	if (!EVP_DigestInit_ex(&ctx, Hash, NULL) ||
  	    !EVP_DigestUpdate(&ctx, zeroes, sizeof zeroes) ||
  	    !EVP_DigestUpdate(&ctx, mHash, hLen))
  		goto err;
  	if (maskedDBLen - i) {
  		if (!EVP_DigestUpdate(&ctx, DB + i, maskedDBLen - i))
  			goto err;
  	}
  	if (!EVP_DigestFinal_ex(&ctx, H_, NULL))
  		goto err;
  	if (memcmp(H_, H, hLen)) {
  		RSAerr(RSA_F_RSA_VERIFY_PKCS1_PSS_MGF1, RSA_R_BAD_SIGNATURE);
  		ret = 0;
  	} else
  		ret = 1;
  
  err:
  	free(DB);
  	EVP_MD_CTX_cleanup(&ctx);
  
  	return ret;
  }
  
  int
  RSA_padding_add_PKCS1_PSS(RSA *rsa, unsigned char *EM,
      const unsigned char *mHash, const EVP_MD *Hash, int sLen)
  {
  	return RSA_padding_add_PKCS1_PSS_mgf1(rsa, EM, mHash, Hash, NULL, sLen);
  }
  
  int
  RSA_padding_add_PKCS1_PSS_mgf1(RSA *rsa, unsigned char *EM,
      const unsigned char *mHash, const EVP_MD *Hash, const EVP_MD *mgf1Hash,
      int sLen)
  {
  	int i;
  	int ret = 0;
  	int hLen, maskedDBLen, MSBits, emLen;
  	unsigned char *H, *salt = NULL, *p;
  	EVP_MD_CTX ctx;
  
  	if (mgf1Hash == NULL)
  		mgf1Hash = Hash;
  
  	hLen = EVP_MD_size(Hash);
  	if (hLen < 0)
  		goto err;
  	/*
  	 * Negative sLen has special meanings:
  	 *	-1	sLen == hLen
  	 *	-2	salt length is maximized
  	 *	-N	reserved
  	 */
  	if (sLen == -1)
  		sLen = hLen;
  	else if (sLen == -2)
  		sLen = -2;
  	else if (sLen < -2) {
  		RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_PSS_MGF1,
  		    RSA_R_SLEN_CHECK_FAILED);
  		goto err;
  	}
  
  	MSBits = (BN_num_bits(rsa->n) - 1) & 0x7;
  	emLen = RSA_size(rsa);
  	if (MSBits == 0) {
  		*EM++ = 0;
  		emLen--;
  	}
  	if (sLen == -2)
  		sLen = emLen - hLen - 2;
  	else if (emLen < (hLen + sLen + 2)) {
  		RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_PSS_MGF1,
  		    RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE);
  		goto err;
  	}
  	if (sLen > 0) {
  		salt = malloc(sLen);
  		if (!salt) {
  			RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_PSS_MGF1,
  			    ERR_R_MALLOC_FAILURE);
  			goto err;
  		}
  		if (RAND_bytes(salt, sLen) <= 0)
  			goto err;
  	}
  	maskedDBLen = emLen - hLen - 1;
  	H = EM + maskedDBLen;
  	EVP_MD_CTX_init(&ctx);
  	if (!EVP_DigestInit_ex(&ctx, Hash, NULL) ||
  	    !EVP_DigestUpdate(&ctx, zeroes, sizeof zeroes) ||
  	    !EVP_DigestUpdate(&ctx, mHash, hLen))
  		goto err;
  	if (sLen && !EVP_DigestUpdate(&ctx, salt, sLen))
  		goto err;
  	if (!EVP_DigestFinal_ex(&ctx, H, NULL))
  		goto err;
  	EVP_MD_CTX_cleanup(&ctx);
  
  	/* Generate dbMask in place then perform XOR on it */
  	if (PKCS1_MGF1(EM, maskedDBLen, H, hLen, mgf1Hash))
  		goto err;
  
  	p = EM;
  
  	/*
  	 * Initial PS XORs with all zeroes which is a NOP so just update
  	 * pointer. Note from a test above this value is guaranteed to
  	 * be non-negative.
  	 */
  	p += emLen - sLen - hLen - 2;
  	*p++ ^= 0x1;
  	if (sLen > 0) {
  		for (i = 0; i < sLen; i++)
  			*p++ ^= salt[i];
  	}
  	if (MSBits)
  		EM[0] &= 0xFF >> (8 - MSBits);
  
  	/* H is already in place so just set final 0xbc */
  	EM[emLen - 1] = 0xbc;
  
  	ret = 1;
  
  err:
  	free(salt);
  
  	return ret;
  }
  