/*
  This file is part of TALER
  (C) 2014 Christian Grothoff (and other contributing authors)

  TALER is free software; you can redistribute it and/or modify it under the
  terms of the GNU General Public License as published by the Free Software
  Foundation; either version 3, or (at your option) any later version.

  TALER is distributed in the hope that it will be useful, but WITHOUT ANY
  WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
  A PARTICULAR PURPOSE.  See the GNU General Public License for more details.

  You should have received a copy of the GNU General Public License along with
  TALER; see the file COPYING.  If not, If not, see <http://www.gnu.org/licenses/>
*/
/**
 * @file util/crypto.c
 * @brief Cryptographic utility functions
 * @author Sree Harsha Totakura <sreeharsha@totakura.in>
 * @author Florian Dold
 * @author Benedikt Mueller
 * @author Christian Grothoff
 */
#include "platform.h"
#include "taler_util.h"
#include <gnunet/gnunet_util_lib.h>
#include <gcrypt.h>


/**
 * Function called by libgcrypt on serious errors.
 * Prints an error message and aborts the process.
 *
 * @param cls NULL
 * @param wtf unknown
 * @param msg error message
 */
static void
fatal_error_handler (void *cls,
                     int wtf,
                     const char *msg)
{
  LOG_ERROR ("Fatal error in libgcrypt: %s\n",
             msg);
  abort();
}


/**
 * Initialize libgcrypt.
 */
void
TALER_gcrypt_init ()
{
  gcry_set_fatalerror_handler (&fatal_error_handler, NULL);
  TALER_assert_as (gcry_check_version (NEED_LIBGCRYPT_VERSION),
                   "libgcrypt version mismatch");
  /* Disable secure memory.  */
  gcry_control (GCRYCTL_DISABLE_SECMEM, 0);
  gcry_control (GCRYCTL_INITIALIZATION_FINISHED, 0);
}


/**
 * Derive symmetric key material for refresh operations from
 * a given shared secret for link decryption.
 *
 * @param secret the shared secret
 * @param[out] iv set to initialization vector
 * @param[out] skey set to session key
 */
static void
derive_refresh_key (const struct TALER_LinkSecret *secret,
                    struct GNUNET_CRYPTO_SymmetricInitializationVector *iv,
                    struct GNUNET_CRYPTO_SymmetricSessionKey *skey)
{
  static const char ctx_key[] = "taler-link-skey";
  static const char ctx_iv[] = "taler-link-iv";

  GNUNET_assert (GNUNET_YES ==
                 GNUNET_CRYPTO_kdf (skey, sizeof (struct GNUNET_CRYPTO_SymmetricSessionKey),
                                    ctx_key, strlen (ctx_key),
                                    secret, sizeof (struct TALER_LinkSecret),
                                    NULL, 0));
  GNUNET_assert (GNUNET_YES ==
                 GNUNET_CRYPTO_kdf (iv, sizeof (struct GNUNET_CRYPTO_SymmetricInitializationVector),
                                    ctx_iv, strlen (ctx_iv),
                                    secret, sizeof (struct TALER_LinkSecret),
                                    NULL, 0));
}


/**
 * Derive symmetric key material for refresh operations from
 * a given shared secret for key decryption.
 *
 * @param secret the shared secret
 * @param[out] iv set to initialization vector
 * @param[out] skey set to session key
 */
static void
derive_transfer_key (const struct TALER_TransferSecret *secret,
                     struct GNUNET_CRYPTO_SymmetricInitializationVector *iv,
                     struct GNUNET_CRYPTO_SymmetricSessionKey *skey)
{
  static const char ctx_key[] = "taler-transfer-skey";
  static const char ctx_iv[] = "taler-transfer-iv";

  GNUNET_assert (GNUNET_YES ==
                 GNUNET_CRYPTO_kdf (skey, sizeof (struct GNUNET_CRYPTO_SymmetricSessionKey),
                                    ctx_key, strlen (ctx_key),
                                    secret, sizeof (struct TALER_TransferSecret),
                                    NULL, 0));
  GNUNET_assert (GNUNET_YES ==
                 GNUNET_CRYPTO_kdf (iv, sizeof (struct GNUNET_CRYPTO_SymmetricInitializationVector),
                                    ctx_iv, strlen (ctx_iv),
                                    secret, sizeof (struct TALER_TransferSecret),
                                    NULL, 0));
}


/**
 * Use the @a trans_sec (from ECDHE) to decrypt the @a secret_enc
 * to obtain the @a secret to decrypt the linkage data.
 *
 * @param secret_enc encrypted secret
 * @param trans_sec transfer secret
 * @param secret shared secret for refresh link decryption
 * @return #GNUNET_OK on success
 */
int
TALER_transfer_decrypt (const struct TALER_EncryptedLinkSecret *secret_enc,
                        const struct TALER_TransferSecret *trans_sec,
                        struct TALER_LinkSecret *secret)
{
  struct GNUNET_CRYPTO_SymmetricInitializationVector iv;
  struct GNUNET_CRYPTO_SymmetricSessionKey skey;

  GNUNET_assert (sizeof (struct TALER_EncryptedLinkSecret) ==
                 sizeof (struct TALER_LinkSecret));
  derive_transfer_key (trans_sec, &iv, &skey);
  return GNUNET_CRYPTO_symmetric_decrypt (secret_enc,
                                          sizeof (struct TALER_LinkSecret),
                                          &skey,
                                          &iv,
                                          secret);
}


/**
 * Use the @a trans_sec (from ECDHE) to encrypt the @a secret
 * to obtain the @a secret_enc.
 *
 * @param secret shared secret for refresh link decryption
 * @param trans_sec transfer secret
 * @param secret_enc[out] encrypted secret
 * @return #GNUNET_OK on success
 */
int
TALER_transfer_encrypt (const struct TALER_LinkSecret *secret,
                        const struct TALER_TransferSecret *trans_sec,
                        struct TALER_EncryptedLinkSecret *secret_enc)
{
  struct GNUNET_CRYPTO_SymmetricInitializationVector iv;
  struct GNUNET_CRYPTO_SymmetricSessionKey skey;

  GNUNET_assert (sizeof (struct TALER_EncryptedLinkSecret) ==
                 sizeof (struct TALER_LinkSecret));
  derive_transfer_key (trans_sec, &iv, &skey);
  return GNUNET_CRYPTO_symmetric_encrypt (secret,
                                          sizeof (struct TALER_LinkSecret),
                                          &skey,
                                          &iv,
                                          secret_enc);
}


/**
 * Decrypt refresh link information.
 *
 * @param input encrypted refresh link data
 * @param secret shared secret to use for decryption
 * @return NULL on error
 */
struct TALER_RefreshLinkDecrypted *
TALER_refresh_decrypt (const struct TALER_RefreshLinkEncrypted *input,
                       const struct TALER_LinkSecret *secret)
{
  struct TALER_RefreshLinkDecrypted *ret;
  struct GNUNET_CRYPTO_SymmetricInitializationVector iv;
  struct GNUNET_CRYPTO_SymmetricSessionKey skey;
  size_t buf_size = input->blinding_key_enc_size
    + sizeof (struct GNUNET_CRYPTO_EcdsaPrivateKey);
  char buf[buf_size];

  GNUNET_assert (input->blinding_key_enc == (const char *) &input[1]);
  derive_refresh_key (secret, &iv, &skey);
  if (GNUNET_OK !=
      GNUNET_CRYPTO_symmetric_decrypt (input->coin_priv_enc,
                                       buf_size,
                                       &skey,
                                       &iv,
                                       buf))
    return NULL;
  ret = GNUNET_new (struct TALER_RefreshLinkDecrypted);
  memcpy (&ret->coin_priv,
          buf,
          sizeof (struct GNUNET_CRYPTO_EcdsaPrivateKey));
  ret->blinding_key
    = GNUNET_CRYPTO_rsa_blinding_key_decode (&buf[sizeof (struct GNUNET_CRYPTO_EcdsaPrivateKey)],
                                             input->blinding_key_enc_size);
  if (NULL == ret->blinding_key)
  {
    GNUNET_free (ret);
    return NULL;
  }
  return ret;
}


/**
 * Encrypt refresh link information.
 *
 * @param input plaintext refresh link data
 * @param secret shared secret to use for encryption
 * @return NULL on error (should never happen)
 */
struct TALER_RefreshLinkEncrypted *
TALER_refresh_encrypt (const struct TALER_RefreshLinkDecrypted *input,
                       const struct TALER_LinkSecret *secret)
{
  char *b_buf;
  size_t b_buf_size;
  struct GNUNET_CRYPTO_SymmetricInitializationVector iv;
  struct GNUNET_CRYPTO_SymmetricSessionKey skey;
  struct TALER_RefreshLinkEncrypted *ret;

  derive_refresh_key (secret, &iv, &skey);
  b_buf_size = GNUNET_CRYPTO_rsa_blinding_key_encode (input->blinding_key,
                                                      &b_buf);
  ret = GNUNET_malloc (sizeof (struct TALER_RefreshLinkEncrypted) +
                       b_buf_size);
  ret->blinding_key_enc = (const char *) &ret[1];
  ret->blinding_key_enc_size = b_buf_size;
  {
    size_t buf_size = b_buf_size + sizeof (struct GNUNET_CRYPTO_EcdsaPrivateKey);
    char buf[buf_size];

    memcpy (buf,
            &input->coin_priv,
            sizeof (struct GNUNET_CRYPTO_EcdsaPrivateKey));
    memcpy (&buf[sizeof (struct GNUNET_CRYPTO_EcdsaPrivateKey)],
            b_buf,
            b_buf_size);

    if (GNUNET_OK !=
        GNUNET_CRYPTO_symmetric_encrypt (buf,
                                         buf_size,
                                         &skey,
                                         &iv,
                                         ret->coin_priv_enc))
    {
      GNUNET_free (ret);
      return NULL;
    }
  }
  return ret;
}


/**
 * Check if a coin is valid; that is, whether the denomination key exists,
 * is not expired, and the signature is correct.
 *
 * @param coin_public_info the coin public info to check for validity
 * @return #GNUNET_YES if the coin is valid,
 *         #GNUNET_NO if it is invalid
 *         #GNUNET_SYSERROR if an internal error occured
 */
int
TALER_test_coin_valid (const struct TALER_CoinPublicInfo *coin_public_info)
{
  struct GNUNET_HashCode c_hash;

  /* FIXME: we had envisioned a more complex scheme... */
  GNUNET_CRYPTO_hash (&coin_public_info->coin_pub,
                      sizeof (struct GNUNET_CRYPTO_EcdsaPublicKey),
                      &c_hash);
  if (GNUNET_OK !=
      GNUNET_CRYPTO_rsa_verify (&c_hash,
                                coin_public_info->denom_sig,
                                coin_public_info->denom_pub))
  {
    GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
                "coin signature is invalid\n");
    return GNUNET_NO;
  }
  return GNUNET_YES;
}


/* end of crypto.c */