src/pk/rsa/rsa_sign_hash.c

/* LibTomCrypt, modular cryptographic library -- Tom St Denis
 *
 * LibTomCrypt is a library that provides various cryptographic
 * algorithms in a highly modular and flexible manner.
 *
 * The library is free for all purposes without any express
 * guarantee it works.
 *
 * Tom St Denis, tomstdenis@gmail.com, http://libtomcrypt.com
 */
#include "tomcrypt.h"

/**
  @file rsa_sign_hash.c
  RSA PKCS #1 v1.5 and v2 PSS sign hash, Tom St Denis and Andreas Lange
*/

#ifdef MRSA

/**
  PKCS #1 pad then sign
  @param in        The hash to sign
  @param inlen     The length of the hash to sign (octets)
  @param out       [out] The signature
  @param outlen    [in/out] The max size and resulting size of the signature
  @param padding   Type of padding (LTC_PKCS_1_PSS or LTC_PKCS_1_V1_5)
  @param prng      An active PRNG state
  @param prng_idx  The index of the PRNG desired
  @param hash_idx  The index of the hash desired
  @param saltlen   The length of the salt desired (octets)
  @param key       The private RSA key to use
  @return CRYPT_OK if successful
*/
int rsa_sign_hash_ex(const unsigned char *in,       unsigned long  inlen,
                           unsigned char *out,      unsigned long *outlen,
                           int            padding,
                           prng_state    *prng,     int            prng_idx,
                           int            hash_idx, unsigned long  saltlen,
                           rsa_key *key)
{
   unsigned long modulus_bitlen, modulus_bytelen, x, y;
   int           err;

   LTC_ARGCHK(in       != NULL);
   LTC_ARGCHK(out      != NULL);
   LTC_ARGCHK(outlen   != NULL);
   LTC_ARGCHK(key      != NULL);

   /* valid padding? */
   if ((padding != LTC_PKCS_1_V1_5) && (padding != LTC_PKCS_1_PSS)) {
     return CRYPT_PK_INVALID_PADDING;
   }

   if (padding == LTC_PKCS_1_PSS) {
     /* valid prng and hash ? */
     if ((err = prng_is_valid(prng_idx)) != CRYPT_OK) {
        return err;
     }
     if ((err = hash_is_valid(hash_idx)) != CRYPT_OK) {
        return err;
     }
   }

   /* get modulus len in bits */
   modulus_bitlen = mp_count_bits((key->N));

  /* outlen must be at least the size of the modulus */
  modulus_bytelen = mp_unsigned_bin_size((key->N));
  if (modulus_bytelen > *outlen) {
     *outlen = modulus_bytelen;
     return CRYPT_BUFFER_OVERFLOW;
  }

  if (padding == LTC_PKCS_1_PSS) {
    /* PSS pad the key */
    x = *outlen;
    if ((err = pkcs_1_pss_encode(in, inlen, saltlen, prng, prng_idx,
                                 hash_idx, modulus_bitlen, out, &x)) != CRYPT_OK) {
       return err;
    }
  } else {
    /* PKCS #1 v1.5 pad the hash */
    unsigned char *tmpin;
    ltc_asn1_list digestinfo[2], siginfo[2];

    /* not all hashes have OIDs... so sad */
    if (hash_descriptor[hash_idx].OIDlen == 0) {
       return CRYPT_INVALID_ARG;
    }

    /* construct the SEQUENCE 
      SEQUENCE {
         SEQUENCE {hashoid OID
                   blah    NULL
         }
         hash    OCTET STRING 
      }
   */
    LTC_SET_ASN1(digestinfo, 0, LTC_ASN1_OBJECT_IDENTIFIER, hash_descriptor[hash_idx].OID, hash_descriptor[hash_idx].OIDlen);
    LTC_SET_ASN1(digestinfo, 1, LTC_ASN1_NULL,              NULL,                          0);
    LTC_SET_ASN1(siginfo,    0, LTC_ASN1_SEQUENCE,          digestinfo,                    2);
    LTC_SET_ASN1(siginfo,    1, LTC_ASN1_OCTET_STRING,      in,                            inlen);

    /* allocate memory for the encoding */
    y = mp_unsigned_bin_size(key->N);
    tmpin = XMALLOC(y);
    if (tmpin == NULL) {
       return CRYPT_MEM;
    }

    if ((err = der_encode_sequence(siginfo, 2, tmpin, &y)) != CRYPT_OK) {
       XFREE(tmpin);
       return err;
    }

    x = *outlen;
    if ((err = pkcs_1_v1_5_encode(tmpin, y, LTC_PKCS_1_EMSA,
                                  modulus_bitlen, NULL, 0,
                                  out, &x)) != CRYPT_OK) {
      XFREE(tmpin);
      return err;
    }
    XFREE(tmpin);
  }

  /* RSA encode it */
  return ltc_mp.rsa_me(out, x, out, outlen, PK_PRIVATE, key);
}

#endif /* MRSA */

/* $Source: /cvs/libtom/libtomcrypt/src/pk/rsa/rsa_sign_hash.c,v $ */
/* $Revision: 1.9 $ */
/* $Date: 2006/11/09 23:15:39 $ */