ecc_import.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.
 */

/* 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_import.c
  ECC Crypto, Tom St Denis
*/

#ifdef LTC_MECC

static int _is_point(ecc_key *key)
{
   void *prime, *b, *t1, *t2;
   int err;

   if ((err = mp_init_multi(&prime, &b, &t1, &t2, NULL)) != CRYPT_OK) {
      return err;
   }

   /* load prime and b */
   if ((err = mp_read_radix(prime, key->dp->prime, 16)) != CRYPT_OK)                          { goto error; }
   if ((err = mp_read_radix(b, key->dp->B, 16)) != CRYPT_OK)                                  { goto error; }

   /* compute y^2 */
   if ((err = mp_sqr(key->pubkey.y, t1)) != CRYPT_OK)                                         { goto error; }

   /* compute x^3 */
   if ((err = mp_sqr(key->pubkey.x, t2)) != CRYPT_OK)                                         { goto error; }
   if ((err = mp_mod(t2, prime, t2)) != CRYPT_OK)                                             { goto error; }
   if ((err = mp_mul(key->pubkey.x, t2, t2)) != CRYPT_OK)                                     { goto error; }

   /* compute y^2 - x^3 */
   if ((err = mp_sub(t1, t2, t1)) != CRYPT_OK)                                                { goto error; }

   /* compute y^2 - x^3 + 3x */
   if ((err = mp_add(t1, key->pubkey.x, t1)) != CRYPT_OK)                                     { goto error; }
   if ((err = mp_add(t1, key->pubkey.x, t1)) != CRYPT_OK)                                     { goto error; }
   if ((err = mp_add(t1, key->pubkey.x, t1)) != CRYPT_OK)                                     { goto error; }
   if ((err = mp_mod(t1, prime, t1)) != CRYPT_OK)                                             { goto error; }
   while (mp_cmp_d(t1, 0) == LTC_MP_LT) {
      if ((err = mp_add(t1, prime, t1)) != CRYPT_OK)                                          { goto error; }
   }
   while (mp_cmp(t1, prime) != LTC_MP_LT) {
      if ((err = mp_sub(t1, prime, t1)) != CRYPT_OK)                                          { goto error; }
   }

   /* compare to b */
   if (mp_cmp(t1, b) != LTC_MP_EQ) {
      err = CRYPT_INVALID_PACKET;
   } else {
      err = CRYPT_OK;
   }

error:
   mp_clear_multi(prime, b, t1, t2, NULL);
   return err;
}

/**
  Import an ECC key from a binary packet
  @param in      The packet to import
  @param inlen   The length of the packet
  @param key     [out] The destination of the import
  @return CRYPT_OK if successful, upon error all allocated memory will be freed
*/
int ecc_import(const unsigned char *in, unsigned long inlen, ecc_key *key)
{
   return ecc_import_ex(in, inlen, key, NULL);
}

/**
  Import an ECC key from a binary packet, using user supplied domain params rather than one of the NIST ones
  @param in      The packet to import
  @param inlen   The length of the packet
  @param key     [out] The destination of the import
  @param dp      pointer to user supplied params; must be the same as the params used when exporting
  @return CRYPT_OK if successful, upon error all allocated memory will be freed
*/
int ecc_import_ex(const unsigned char *in, unsigned long inlen, ecc_key *key, const ltc_ecc_set_type *dp)
{
   unsigned long key_size;
   unsigned char flags[1];
   int           err;

   LTC_ARGCHK(in  != NULL);
   LTC_ARGCHK(key != NULL);
   LTC_ARGCHK(ltc_mp.name != NULL);

   /* init key */
   if (mp_init_multi(&key->pubkey.x, &key->pubkey.y, &key->pubkey.z, &key->k, NULL) != CRYPT_OK) {
      return CRYPT_MEM;
   }

   /* find out what type of key it is */
   err = der_decode_sequence_multi(in, inlen, LTC_ASN1_BIT_STRING, 1UL, flags,
                                              LTC_ASN1_EOL,        0UL, NULL);
   if (err != CRYPT_OK && err != CRYPT_INPUT_TOO_LONG) {
      goto done;
   }


   if (flags[0] == 1) {
      /* private key */
      key->type = PK_PRIVATE;
      if ((err = der_decode_sequence_multi(in, inlen,
                                     LTC_ASN1_BIT_STRING,      1UL, flags,
                                     LTC_ASN1_SHORT_INTEGER,   1UL, &key_size,
                                     LTC_ASN1_INTEGER,         1UL, key->pubkey.x,
                                     LTC_ASN1_INTEGER,         1UL, key->pubkey.y,
                                     LTC_ASN1_INTEGER,         1UL, key->k,
                                     LTC_ASN1_EOL,             0UL, NULL)) != CRYPT_OK) {
         goto done;
      }
   } else if (flags[0] == 0) {
      /* public key */
      key->type = PK_PUBLIC;
      if ((err = der_decode_sequence_multi(in, inlen,
                                     LTC_ASN1_BIT_STRING,      1UL, flags,
                                     LTC_ASN1_SHORT_INTEGER,   1UL, &key_size,
                                     LTC_ASN1_INTEGER,         1UL, key->pubkey.x,
                                     LTC_ASN1_INTEGER,         1UL, key->pubkey.y,
                                     LTC_ASN1_EOL,             0UL, NULL)) != CRYPT_OK) {
         goto done;
      }
   }
   else {
      err = CRYPT_INVALID_PACKET;
      goto done;
   }

   if (dp == NULL) {
     /* find the idx */
     for (key->idx = 0; ltc_ecc_sets[key->idx].size && (unsigned long)ltc_ecc_sets[key->idx].size != key_size; ++key->idx);
     if (ltc_ecc_sets[key->idx].size == 0) {
       err = CRYPT_INVALID_PACKET;
       goto done;
     }
     key->dp = &ltc_ecc_sets[key->idx];
   } else {
     key->idx = -1;
     key->dp = dp;
   }
   /* set z */
   if ((err = mp_set(key->pubkey.z, 1)) != CRYPT_OK) { goto done; }

   /* is it a point on the curve?  */
   if ((err = _is_point(key)) != CRYPT_OK) {
      goto done;
   }

   /* we're good */
   return CRYPT_OK;
done:
   mp_clear_multi(key->pubkey.x, key->pubkey.y, key->pubkey.z, key->k, NULL);
   return err;
}
#endif