/* 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@iahu.ca, http://libtomcrypt.org */int dh_encrypt_key(const unsigned char *inkey, unsigned long keylen,                         unsigned char *out,  unsigned long *len,                         prng_state *prng, int wprng, int hash,                         dh_key *key){    unsigned char pub_expt[768], dh_shared[768], skey[MAXBLOCKSIZE];    dh_key pubkey;    unsigned long x, y, z, hashsize, pubkeysize;    int err;    _ARGCHK(inkey != NULL);    _ARGCHK(out   != NULL);    _ARGCHK(len   != NULL);    _ARGCHK(key   != NULL);    /* check that wprng/hash are not invalid */    if ((err = prng_is_valid(wprng)) != CRYPT_OK) {       return err;    }    if ((err = hash_is_valid(hash)) != CRYPT_OK) {       return err;    }    if (keylen > hash_descriptor[hash].hashsize)  {        return CRYPT_INVALID_HASH;    }    /* make a random key and export the public copy */    if ((err = dh_make_key(prng, wprng, dh_get_size(key), &pubkey)) != CRYPT_OK) {       return err;    }    pubkeysize = sizeof(pub_expt);    if ((err = dh_export(pub_expt, &pubkeysize, PK_PUBLIC, &pubkey)) != CRYPT_OK) {       dh_free(&pubkey);       return err;    }    /* now check if the out buffer is big enough */    if (*len < (1 + 4 + 4 + PACKET_SIZE + pubkeysize + keylen)) {       dh_free(&pubkey);       return CRYPT_BUFFER_OVERFLOW;    }    /* make random key */    hashsize  = hash_descriptor[hash].hashsize;    x = (unsigned long)sizeof(dh_shared);    if ((err = dh_shared_secret(&pubkey, key, dh_shared, &x)) != CRYPT_OK) {       dh_free(&pubkey);       return err;    }    dh_free(&pubkey);    z = sizeof(skey);    if ((err = hash_memory(hash, dh_shared, x, skey, &z)) != CRYPT_OK) {       return err;    }    /* store header */    packet_store_header(out, PACKET_SECT_DH, PACKET_SUB_ENC_KEY);    /* output header */    y = PACKET_SIZE;    /* size of hash name and the name itself */    out[y++] = hash_descriptor[hash].ID;    /* length of DH pubkey and the key itself */    STORE32L(pubkeysize, out+y);    y += 4;    for (x = 0; x < pubkeysize; x++, y++) {        out[y] = pub_expt[x];    }    /* Store the encrypted key */    STORE32L(keylen, out+y);    y += 4;    for (x = 0; x < keylen; x++, y++) {      out[y] = skey[x] ^ inkey[x];    }    *len = y;#ifdef CLEAN_STACK    /* clean up */    zeromem(pub_expt, sizeof(pub_expt));    zeromem(dh_shared, sizeof(dh_shared));    zeromem(skey, sizeof(skey));#endif    return CRYPT_OK;}int dh_decrypt_key(const unsigned char *in, unsigned long inlen,                         unsigned char *outkey, unsigned long *keylen,                          dh_key *key){   unsigned char shared_secret[768], skey[MAXBLOCKSIZE];   unsigned long x, y, z,hashsize, keysize;   int  hash, err;   dh_key pubkey;   _ARGCHK(in     != NULL);   _ARGCHK(outkey != NULL);   _ARGCHK(keylen != NULL);   _ARGCHK(key    != NULL);   /* right key type? */   if (key->type != PK_PRIVATE) {      return CRYPT_PK_NOT_PRIVATE;   }   /* check if initial header should fit */   if (inlen < PACKET_SIZE+1+4+4) {      return CRYPT_INVALID_PACKET;   } else {      inlen -= PACKET_SIZE+1+4+4;   }   /* is header correct? */   if ((err = packet_valid_header((unsigned char *)in, PACKET_SECT_DH, PACKET_SUB_ENC_KEY)) != CRYPT_OK)  {      return err;   }   /* now lets get the hash name */   y = PACKET_SIZE;   hash = find_hash_id(in[y++]);   if (hash == -1) {      return CRYPT_INVALID_HASH;   }   /* common values */   hashsize  = hash_descriptor[hash].hashsize;   /* get public key */   LOAD32L(x, in+y);      /* now check if the imported key will fit */   if (inlen < x) {      return CRYPT_INVALID_PACKET;   } else {      inlen -= x;   }      y += 4;   if ((err = dh_import(in+y, x, &pubkey)) != CRYPT_OK) {      return err;   }   y += x;   /* make shared key */   x = (unsigned long)sizeof(shared_secret);   if ((err = dh_shared_secret(key, &pubkey, shared_secret, &x)) != CRYPT_OK) {      dh_free(&pubkey);      return err;   }   dh_free(&pubkey);   z = sizeof(skey);   if ((err = hash_memory(hash, shared_secret, x, skey, &z)) != CRYPT_OK) {      return err;   }   /* load in the encrypted key */   LOAD32L(keysize, in+y);      /* will the outkey fit as part of the input */   if (inlen < keysize) {      return CRYPT_INVALID_PACKET;   } else {      inlen -= keysize;   }      if (keysize > *keylen) {       err = CRYPT_BUFFER_OVERFLOW;       goto done;   }   y += 4;   *keylen = keysize;   for (x = 0; x < keysize; x++, y++) {      outkey[x] = skey[x] ^ in[y];   }   err = CRYPT_OK;done:#ifdef CLEAN_STACK   zeromem(shared_secret, sizeof(shared_secret));   zeromem(skey, sizeof(skey));#endif   return err;}/* perform an ElGamal Signature of a hash  * * The math works as follows.  x is the private key, M is the message to sign  1.  pick a random k 2.  compute a = g^k mod p 3.  compute b = (M - xa)/k mod p 4.  Send (a,b)  Now to verify with y=g^x mod p, a and b  1.  compute y^a * a^b = g^(xa) * g^(k*(M-xa)/k)                       = g^(xa + (M - xa))                       = g^M [all mod p]                        2.  Compare against g^M mod p [based on input hash]. 3.  If result of #2 == result of #1 then signature valid */int dh_sign_hash(const unsigned char *in,  unsigned long inlen,                       unsigned char *out, unsigned long *outlen,                       prng_state *prng, int wprng, dh_key *key){   mp_int a, b, k, m, g, p, p1, tmp;   unsigned char buf[520];   unsigned long x, y;   int err;   _ARGCHK(in     != NULL);   _ARGCHK(out    != NULL);   _ARGCHK(outlen != NULL);   _ARGCHK(key    != NULL);   /* check parameters */   if (key->type != PK_PRIVATE) {      return CRYPT_PK_NOT_PRIVATE;   }   if ((err = prng_is_valid(wprng)) != CRYPT_OK) {      return err;   }   /* is the IDX valid ?  */   if (is_valid_idx(key->idx) != 1) {      return CRYPT_PK_INVALID_TYPE;   }   /* make up a random value k,    * since the order of the group is prime    * we need not check if gcd(k, r) is 1     */   if (prng_descriptor[wprng].read(buf, sets[key->idx].size, prng) !=        (unsigned long)(sets[key->idx].size)) {      return CRYPT_ERROR_READPRNG;   }   /* init bignums */   if ((err = mp_init_multi(&a, &b, &k, &m, &p, &g, &p1, &tmp, NULL)) != MP_OKAY) {       return mpi_to_ltc_error(err);   }   /* load k and m */   if ((err = mp_read_unsigned_bin(&m, (unsigned char *)in, inlen)) != MP_OKAY)        { goto error; }#ifdef FAST_PK      if ((err = mp_read_unsigned_bin(&k, buf, MIN(32,sets[key->idx].size))) != MP_OKAY)  { goto error; }#else      if ((err = mp_read_unsigned_bin(&k, buf, sets[key->idx].size)) != MP_OKAY)          { goto error; }#endif     /* load g, p and p1 */   if ((err = mp_read_radix(&g, sets[key->idx].base, 64)) != MP_OKAY)               { goto error; }   if ((err = mp_read_radix(&p, sets[key->idx].prime, 64)) != MP_OKAY)              { goto error; }   if ((err = mp_sub_d(&p, 1, &p1)) != MP_OKAY)                                     { goto error; }   if ((err = mp_div_2(&p1, &p1)) != MP_OKAY)                                       { goto error; } /* p1 = (p-1)/2 */   /* now get a = g^k mod p */   if ((err = mp_exptmod(&g, &k, &p, &a)) != MP_OKAY)                               { goto error; }   /* now find M = xa + kb mod p1 or just b = (M - xa)/k mod p1 */   if ((err = mp_invmod(&k, &p1, &k)) != MP_OKAY)                                   { goto error; } /* k = 1/k mod p1 */   if ((err = mp_mulmod(&a, &key->x, &p1, &tmp)) != MP_OKAY)                        { goto error; } /* tmp = xa */   if ((err = mp_submod(&m, &tmp, &p1, &tmp)) != MP_OKAY)                           { goto error; } /* tmp = M - xa */   if ((err = mp_mulmod(&k, &tmp, &p1, &b)) != MP_OKAY)                             { goto error; } /* b = (M - xa)/k */      /* check for overflow */   if ((unsigned long)(PACKET_SIZE + 4 + 4 + mp_unsigned_bin_size(&a) + mp_unsigned_bin_size(&b)) > *outlen) {      err = CRYPT_BUFFER_OVERFLOW;      goto done;   }      /* store header  */   y = PACKET_SIZE;   /* now store them both (a,b) */   x = (unsigned long)mp_unsigned_bin_size(&a);   STORE32L(x, out+y);  y += 4;   if ((err = mp_to_unsigned_bin(&a, out+y)) != MP_OKAY)                            { goto error; }   y += x;   x = (unsigned long)mp_unsigned_bin_size(&b);   STORE32L(x, out+y);  y += 4;   if ((err = mp_to_unsigned_bin(&b, out+y)) != MP_OKAY)                            { goto error; }   y += x;   /* check if size too big */   if (*outlen < y) {      err = CRYPT_BUFFER_OVERFLOW;      goto done;   }   /* store header */   packet_store_header(out, PACKET_SECT_DH, PACKET_SUB_SIGNED);   *outlen = y;   err = CRYPT_OK;   goto done;error:   err = mpi_to_ltc_error(err);done:   mp_clear_multi(&tmp, &p1, &g, &p, &m, &k, &b, &a, NULL);   return err;}/* verify the signature in sig of the given hash */int dh_verify_hash(const unsigned char *sig, unsigned long siglen,                   const unsigned char *hash, unsigned long hashlen,                          int *stat, dh_key *key){   mp_int a, b, p, g, m, tmp;   unsigned long x, y;   int err;   _ARGCHK(sig  != NULL);   _ARGCHK(hash != NULL);   _ARGCHK(stat != NULL);   _ARGCHK(key  != NULL);   /* default to invalid */   *stat = 0;   /* check initial input length */   if (siglen < PACKET_SIZE+4+4) {      return CRYPT_INVALID_PACKET;   }    /* header ok? */   if ((err = packet_valid_header((unsigned char *)sig, PACKET_SECT_DH, PACKET_SUB_SIGNED)) != CRYPT_OK) {      return err;   }      /* get hash out of packet */   y = PACKET_SIZE;   /* init all bignums */   if ((err = mp_init_multi(&a, &p, &b, &g, &m, &tmp, NULL)) != MP_OKAY) {       return mpi_to_ltc_error(err);   }   /* load a and b */   INPUT_BIGNUM(&a, sig, x, y, siglen);   INPUT_BIGNUM(&b, sig, x, y, siglen);   /* load p and g */   if ((err = mp_read_radix(&p, sets[key->idx].prime, 64)) != MP_OKAY)              { goto error1; }   if ((err = mp_read_radix(&g, sets[key->idx].base, 64)) != MP_OKAY)               { goto error1; }   /* load m */   if ((err = mp_read_unsigned_bin(&m, (unsigned char *)hash, hashlen)) != MP_OKAY) { goto error1; }   /* find g^m mod p */   if ((err = mp_exptmod(&g, &m, &p, &m)) != MP_OKAY)                { goto error1; } /* m = g^m mod p */   /* find y^a * a^b */   if ((err = mp_exptmod(&key->y, &a, &p, &tmp)) != MP_OKAY)         { goto error1; } /* tmp = y^a mod p */   if ((err = mp_exptmod(&a, &b, &p, &a)) != MP_OKAY)                { goto error1; } /* a = a^b mod p */   if ((err = mp_mulmod(&a, &tmp, &p, &a)) != MP_OKAY)               { goto error1; } /* a = y^a * a^b mod p */   /* y^a * a^b == g^m ??? */   if (mp_cmp(&a, &m) == 0) {      *stat = 1;   }   /* clean up */   err = CRYPT_OK;   goto done;error1:   err = mpi_to_ltc_error(err);error:done:   mp_clear_multi(&tmp, &m, &g, &p, &b, &a, NULL);   return err;}