text: /* 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
   */
  
  /* Implements ECC over Z/pZ for curve y^2 = x^3 - 3x + b
   *
   * All curves taken from NIST recommendation paper of July 1999
   * Available at http://csrc.nist.gov/cryptval/dss.htm
   */
  #include "tomcrypt.h"
  
  /**
    @file ecc_verify_hash.c
    ECC Crypto, Tom St Denis
  */  
  
  #ifdef MECC
  
  /* verify 
   *
   * w  = s^-1 mod n
   * u1 = xw 
   * u2 = rw
   * X = u1*G + u2*Q
   * v = X_x1 mod n
   * accept if v == r
   */
  
  /**
     Verify an ECC signature
     @param sig         The signature to verify
     @param siglen      The length of the signature (octets)
     @param hash        The hash (message digest) that was signed
     @param hashlen     The length of the hash (octets)
     @param stat        Result of signature, 1==valid, 0==invalid
     @param key         The corresponding public ECC key
     @return CRYPT_OK if successful (even if the signature is not valid)
  */
  int ecc_verify_hash(const unsigned char *sig,  unsigned long siglen,
                      const unsigned char *hash, unsigned long hashlen, 
                      int *stat, ecc_key *key)
  {
     ecc_point    *mG, *mQ;
     void          *r, *s, *v, *w, *u1, *u2, *e, *p, *m;
     void          *mp;
     int           err;
  
     LTC_ARGCHK(sig  != NULL);
     LTC_ARGCHK(hash != NULL);
     LTC_ARGCHK(stat != NULL);
     LTC_ARGCHK(key  != NULL);
  
     /* default to invalid signature */
     *stat = 0;
     mp    = NULL;
  
     /* is the IDX valid ?  */
     if (ltc_ecc_is_valid_idx(key->idx) != 1) {
        return CRYPT_PK_INVALID_TYPE;
     }
  
     /* allocate ints */
     if ((err = mp_init_multi(&r, &s, &v, &w, &u1, &u2, &p, &e, &m, NULL)) != CRYPT_OK) {
        return CRYPT_MEM;
     }
  
     /* allocate points */
     mG = ltc_ecc_new_point();
     mQ = ltc_ecc_new_point();
     if (mQ  == NULL || mG == NULL) {
        err = CRYPT_MEM;
        goto done;
     }
  
     /* parse header */
     if ((err = der_decode_sequence_multi(sig, siglen,
                                    LTC_ASN1_INTEGER, 1UL, r,
                                    LTC_ASN1_INTEGER, 1UL, s,
                                    LTC_ASN1_EOL, 0UL, NULL)) != CRYPT_OK) {
        goto done;
     }
  
     /* get the order */
     if ((err = mp_read_radix(p, (char *)ltc_ecc_sets[key->idx].order, 16)) != CRYPT_OK)                  { goto error; }
  
     /* get the modulus */
     if ((err = mp_read_radix(m, (char *)ltc_ecc_sets[key->idx].prime, 16)) != CRYPT_OK)                  { goto error; }
  
     /* check for zero */
     if (mp_iszero(r) || mp_iszero(s) || mp_cmp(r, p) != LTC_MP_LT || mp_cmp(s, p) != LTC_MP_LT) {
        err = CRYPT_INVALID_PACKET;
        goto done;
     }
  
     /* read hash */
     if ((err = mp_read_unsigned_bin(e, (unsigned char *)hash, (int)hashlen)) != CRYPT_OK)                { goto error; }
  
     /*  w  = s^-1 mod n */
     if ((err = mp_invmod(s, p, w)) != CRYPT_OK)                                                          { goto error; }
  
     /* u1 = ew */
     if ((err = mp_mulmod(e, w, p, u1)) != CRYPT_OK)                                                      { goto error; }
  
     /* u2 = rw */
     if ((err = mp_mulmod(r, w, p, u2)) != CRYPT_OK)                                                      { goto error; }
  
     /* find mG = u1*G */
     if ((err = mp_read_radix(mG->x, (char *)ltc_ecc_sets[key->idx].Gx, 16)) != CRYPT_OK)                 { goto error; }
     if ((err = mp_read_radix(mG->y, (char *)ltc_ecc_sets[key->idx].Gy, 16)) != CRYPT_OK)                 { goto error; }
     mp_set(mG->z, 1);  
     if ((err = ltc_mp.ecc_ptmul(u1, mG, mG, m, 0)) != CRYPT_OK)                                          { goto done; }
  
     /* find mQ = u2*Q */
     if ((err = mp_copy(key->pubkey.x, mQ->x)) != CRYPT_OK)                                               { goto error; }
     if ((err = mp_copy(key->pubkey.y, mQ->y)) != CRYPT_OK)                                               { goto error; }
     if ((err = mp_copy(key->pubkey.z, mQ->z)) != CRYPT_OK)                                               { goto error; }
     if ((err = ltc_mp.ecc_ptmul(u2, mQ, mQ, m, 0)) != CRYPT_OK)                                          { goto done; }
    
     /* find the montgomery mp */
     if ((err = mp_montgomery_setup(m, &mp)) != CRYPT_OK)                                                 { goto error; }
     /* add them */
     if ((err = ltc_mp.ecc_ptadd(mQ, mG, mG, m, mp)) != CRYPT_OK)                                         { goto done; }
     
     /* reduce */
     if ((err = ltc_mp.ecc_map(mG, m, mp)) != CRYPT_OK)                                                   { goto done; }
  
     /* v = X_x1 mod n */
     if ((err = mp_mod(mG->x, p, v)) != CRYPT_OK)                                                         { goto done; }
  
     /* does v == r */
     if (mp_cmp(v, r) == LTC_MP_EQ) {
        *stat = 1;
     }
  
     /* clear up and return */
     err = CRYPT_OK;
     goto done;
  error:
  done:
     ltc_ecc_del_point(mG);
     ltc_ecc_del_point(mQ);
     mp_clear_multi(r, s, v, w, u1, u2, p, e, m, NULL);
     if (mp != NULL) { 
        mp_montgomery_free(mp);
     }
     return err;
  }
  
  #endif
  /* $Source: /cvs/libtom/libtomcrypt/src/pk/ecc/ecc_verify_hash.c,v $ */
  /* $Revision: 1.7 $ */
  /* $Date: 2006/03/31 14:15:35 $ */
  
  