gnunet/src/util/crypto_ecc.c

/*
     This file is part of GNUnet.
     Copyright (C) 2012, 2013, 2015 GNUnet e.V.

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

     GNUnet 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
     Affero General Public License for more details.

     You should have received a copy of the GNU Affero General Public License
     along with this program.  If not, see <http://www.gnu.org/licenses/>.

     SPDX-License-Identifier: AGPL3.0-or-later
 */

/**
 * @file util/crypto_ecc.c
 * @brief public key cryptography (ECC) with libgcrypt
 * @author Christian Grothoff
 */
#include "platform.h"
#include <gcrypt.h>
#include "gnunet_crypto_lib.h"
#include "gnunet_strings_lib.h"
#include "benchmark.h"

#define EXTRA_CHECKS 0

/**
 * Name of the curve we are using.  Note that we have hard-coded
 * structs that use 256 bits, so using a bigger curve will require
 * changes that break stuff badly.  The name of the curve given here
 * must be agreed by all peers and be supported by libgcrypt.
 */
#define CURVE "Ed25519"

#define LOG(kind, ...) GNUNET_log_from (kind, "util-crypto-ecc", __VA_ARGS__)

#define LOG_STRERROR(kind, syscall) \
  GNUNET_log_from_strerror (kind, "util-crypto-ecc", syscall)

#define LOG_STRERROR_FILE(kind, syscall, filename) \
  GNUNET_log_from_strerror_file (kind, "util-crypto-ecc", syscall, filename)

/**
 * Log an error message at log-level 'level' that indicates
 * a failure of the command 'cmd' with the message given
 * by gcry_strerror(rc).
 */
#define LOG_GCRY(level, cmd, rc)                      \
  do                                                  \
  {                                                   \
    LOG (level,                                       \
         _ ("`%s' failed at %s:%d with error: %s\n"), \
         cmd,                                         \
         __FILE__,                                    \
         __LINE__,                                    \
         gcry_strerror (rc));                         \
  } while (0)


/**
 * Extract values from an S-expression.
 *
 * @param array where to store the result(s)
 * @param sexp S-expression to parse
 * @param topname top-level name in the S-expression that is of interest
 * @param elems names of the elements to extract
 * @return 0 on success
 */
static int
key_from_sexp (gcry_mpi_t *array,
               gcry_sexp_t sexp,
               const char *topname,
               const char *elems)
{
  gcry_sexp_t list;
  gcry_sexp_t l2;
  unsigned int idx;

  list = gcry_sexp_find_token (sexp, topname, 0);
  if (! list)
    return 1;
  l2 = gcry_sexp_cadr (list);
  gcry_sexp_release (list);
  list = l2;
  if (! list)
    return 2;

  idx = 0;
  for (const char *s = elems; *s; s++, idx++)
  {
    l2 = gcry_sexp_find_token (list, s, 1);
    if (! l2)
    {
      for (unsigned int i = 0; i < idx; i++)
      {
        gcry_free (array[i]);
        array[i] = NULL;
      }
      gcry_sexp_release (list);
      return 3;     /* required parameter not found */
    }
    array[idx] = gcry_sexp_nth_mpi (l2, 1, GCRYMPI_FMT_USG);
    gcry_sexp_release (l2);
    if (! array[idx])
    {
      for (unsigned int i = 0; i < idx; i++)
      {
        gcry_free (array[i]);
        array[i] = NULL;
      }
      gcry_sexp_release (list);
      return 4;     /* required parameter is invalid */
    }
  }
  gcry_sexp_release (list);
  return 0;
}


/**
 * Convert the given private key from the network format to the
 * S-expression that can be used by libgcrypt.
 *
 * @param priv private key to decode
 * @return NULL on error
 */
static gcry_sexp_t
decode_private_ecdsa_key (const struct GNUNET_CRYPTO_EcdsaPrivateKey *priv)
{
  gcry_sexp_t result;
  int rc;

  rc = gcry_sexp_build (&result,
                        NULL,
                        "(private-key(ecc(curve \"" CURVE "\")"
                        "(d %b)))",
                        (int) sizeof(priv->d),
                        priv->d);
  if (0 != rc)
  {
    LOG_GCRY (GNUNET_ERROR_TYPE_ERROR, "gcry_sexp_build", rc);
    GNUNET_assert (0);
  }
#if EXTRA_CHECKS
  if (0 != (rc = gcry_pk_testkey (result)))
  {
    LOG_GCRY (GNUNET_ERROR_TYPE_ERROR, "gcry_pk_testkey", rc);
    GNUNET_assert (0);
  }
#endif
  return result;
}


/**
 * Convert the given private key from the network format to the
 * S-expression that can be used by libgcrypt.
 *
 * @param priv private key to decode
 * @return NULL on error
 */
static gcry_sexp_t
decode_private_eddsa_key (const struct GNUNET_CRYPTO_EddsaPrivateKey *priv)
{
  gcry_sexp_t result;
  int rc;

  rc = gcry_sexp_build (&result,
                        NULL,
                        "(private-key(ecc(curve \"" CURVE "\")"
                        "(flags eddsa)(d %b)))",
                        (int) sizeof(priv->d),
                        priv->d);
  if (0 != rc)
  {
    LOG_GCRY (GNUNET_ERROR_TYPE_ERROR, "gcry_sexp_build", rc);
    GNUNET_assert (0);
  }
#if EXTRA_CHECKS
  if (0 != (rc = gcry_pk_testkey (result)))
  {
    LOG_GCRY (GNUNET_ERROR_TYPE_ERROR, "gcry_pk_testkey", rc);
    GNUNET_assert (0);
  }
#endif
  return result;
}


/**
 * Convert the given private key from the network format to the
 * S-expression that can be used by libgcrypt.
 *
 * @param priv private key to decode
 * @return NULL on error
 */
static gcry_sexp_t
decode_private_ecdhe_key (const struct GNUNET_CRYPTO_EcdhePrivateKey *priv)
{
  gcry_sexp_t result;
  int rc;

  rc = gcry_sexp_build (&result,
                        NULL,
                        "(private-key(ecc(curve \"" CURVE "\")"
                        "(d %b)))",
                        (int) sizeof(priv->d),
                        priv->d);
  if (0 != rc)
  {
    LOG_GCRY (GNUNET_ERROR_TYPE_ERROR, "gcry_sexp_build", rc);
    GNUNET_assert (0);
  }
#if EXTRA_CHECKS
  if (0 != (rc = gcry_pk_testkey (result)))
  {
    LOG_GCRY (GNUNET_ERROR_TYPE_ERROR, "gcry_pk_testkey", rc);
    GNUNET_assert (0);
  }
#endif
  return result;
}


/**
 * Extract the public key for the given private key.
 *
 * @param priv the private key
 * @param pub where to write the public key
 */
void
GNUNET_CRYPTO_ecdsa_key_get_public (
  const struct GNUNET_CRYPTO_EcdsaPrivateKey *priv,
  struct GNUNET_CRYPTO_EcdsaPublicKey *pub)
{
  gcry_sexp_t sexp;
  gcry_ctx_t ctx;
  gcry_mpi_t q;

  BENCHMARK_START (ecdsa_key_get_public);

  sexp = decode_private_ecdsa_key (priv);
  GNUNET_assert (NULL != sexp);
  GNUNET_assert (0 == gcry_mpi_ec_new (&ctx, sexp, NULL));
  gcry_sexp_release (sexp);
  q = gcry_mpi_ec_get_mpi ("q@eddsa", ctx, 0);
  GNUNET_assert (NULL != q);
  GNUNET_CRYPTO_mpi_print_unsigned (pub->q_y, sizeof(pub->q_y), q);
  gcry_mpi_release (q);
  gcry_ctx_release (ctx);

  BENCHMARK_END (ecdsa_key_get_public);
}


/**
 * Extract the public key for the given private key.
 *
 * @param priv the private key
 * @param pub where to write the public key
 */
void
GNUNET_CRYPTO_eddsa_key_get_public (
  const struct GNUNET_CRYPTO_EddsaPrivateKey *priv,
  struct GNUNET_CRYPTO_EddsaPublicKey *pub)
{
  gcry_sexp_t sexp;
  gcry_ctx_t ctx;
  gcry_mpi_t q;

  BENCHMARK_START (eddsa_key_get_public);

  sexp = decode_private_eddsa_key (priv);
  GNUNET_assert (NULL != sexp);
  GNUNET_assert (0 == gcry_mpi_ec_new (&ctx, sexp, NULL));
  gcry_sexp_release (sexp);
  q = gcry_mpi_ec_get_mpi ("q@eddsa", ctx, 0);
  GNUNET_assert (q);
  GNUNET_CRYPTO_mpi_print_unsigned (pub->q_y, sizeof(pub->q_y), q);
  gcry_mpi_release (q);
  gcry_ctx_release (ctx);

  BENCHMARK_END (eddsa_key_get_public);
}


/**
 * Extract the public key for the given private key.
 *
 * @param priv the private key
 * @param pub where to write the public key
 */
void
GNUNET_CRYPTO_ecdhe_key_get_public (
  const struct GNUNET_CRYPTO_EcdhePrivateKey *priv,
  struct GNUNET_CRYPTO_EcdhePublicKey *pub)
{
  gcry_sexp_t sexp;
  gcry_ctx_t ctx;
  gcry_mpi_t q;

  BENCHMARK_START (ecdhe_key_get_public);

  sexp = decode_private_ecdhe_key (priv);
  GNUNET_assert (NULL != sexp);
  GNUNET_assert (0 == gcry_mpi_ec_new (&ctx, sexp, NULL));
  gcry_sexp_release (sexp);
  q = gcry_mpi_ec_get_mpi ("q@eddsa", ctx, 0);
  GNUNET_assert (q);
  GNUNET_CRYPTO_mpi_print_unsigned (pub->q_y, sizeof(pub->q_y), q);
  gcry_mpi_release (q);
  gcry_ctx_release (ctx);

  BENCHMARK_END (ecdhe_key_get_public);
}


/**
 * Convert a public key to a string.
 *
 * @param pub key to convert
 * @return string representing @a pub
 */
char *
GNUNET_CRYPTO_ecdsa_public_key_to_string (
  const struct GNUNET_CRYPTO_EcdsaPublicKey *pub)
{
  char *pubkeybuf;
  size_t keylen = (sizeof(struct GNUNET_CRYPTO_EcdsaPublicKey)) * 8;
  char *end;

  if (keylen % 5 > 0)
    keylen += 5 - keylen % 5;
  keylen /= 5;
  pubkeybuf = GNUNET_malloc (keylen + 1);
  end =
    GNUNET_STRINGS_data_to_string ((unsigned char *) pub,
                                   sizeof(struct GNUNET_CRYPTO_EcdsaPublicKey),
                                   pubkeybuf,
                                   keylen);
  if (NULL == end)
  {
    GNUNET_free (pubkeybuf);
    return NULL;
  }
  *end = '\0';
  return pubkeybuf;
}


/**
 * Convert a public key to a string.
 *
 * @param pub key to convert
 * @return string representing @a pub
 */
char *
GNUNET_CRYPTO_eddsa_public_key_to_string (
  const struct GNUNET_CRYPTO_EddsaPublicKey *pub)
{
  char *pubkeybuf;
  size_t keylen = (sizeof(struct GNUNET_CRYPTO_EddsaPublicKey)) * 8;
  char *end;

  if (keylen % 5 > 0)
    keylen += 5 - keylen % 5;
  keylen /= 5;
  pubkeybuf = GNUNET_malloc (keylen + 1);
  end =
    GNUNET_STRINGS_data_to_string ((unsigned char *) pub,
                                   sizeof(struct GNUNET_CRYPTO_EddsaPublicKey),
                                   pubkeybuf,
                                   keylen);
  if (NULL == end)
  {
    GNUNET_free (pubkeybuf);
    return NULL;
  }
  *end = '\0';
  return pubkeybuf;
}


/**
 * Convert a private key to a string.
 *
 * @param priv key to convert
 * @return string representing @a pub
 */
char *
GNUNET_CRYPTO_eddsa_private_key_to_string (
  const struct GNUNET_CRYPTO_EddsaPrivateKey *priv)
{
  char *privkeybuf;
  size_t keylen = (sizeof(struct GNUNET_CRYPTO_EddsaPrivateKey)) * 8;
  char *end;

  if (keylen % 5 > 0)
    keylen += 5 - keylen % 5;
  keylen /= 5;
  privkeybuf = GNUNET_malloc (keylen + 1);
  end = GNUNET_STRINGS_data_to_string ((unsigned char *) priv,
                                       sizeof(
                                         struct GNUNET_CRYPTO_EddsaPrivateKey),
                                       privkeybuf,
                                       keylen);
  if (NULL == end)
  {
    GNUNET_free (privkeybuf);
    return NULL;
  }
  *end = '\0';
  return privkeybuf;
}


/**
 * Convert a private key to a string.
 *
 * @param priv key to convert
 * @return string representing @a priv
 */
char *
GNUNET_CRYPTO_ecdsa_private_key_to_string (
  const struct GNUNET_CRYPTO_EcdsaPrivateKey *priv)
{
  char *privkeybuf;
  size_t keylen = (sizeof(struct GNUNET_CRYPTO_EcdsaPrivateKey)) * 8;
  char *end;

  if (keylen % 5 > 0)
    keylen += 5 - keylen % 5;
  keylen /= 5;
  privkeybuf = GNUNET_malloc (keylen + 1);
  end = GNUNET_STRINGS_data_to_string ((unsigned char *) priv,
                                       sizeof(
                                         struct GNUNET_CRYPTO_EcdsaPrivateKey),
                                       privkeybuf,
                                       keylen);
  if (NULL == end)
  {
    GNUNET_free (privkeybuf);
    return NULL;
  }
  *end = '\0';
  return privkeybuf;
}


/**
 * Convert a string representing a public key to a public key.
 *
 * @param enc encoded public key
 * @param enclen number of bytes in @a enc (without 0-terminator)
 * @param pub where to store the public key
 * @return #GNUNET_OK on success
 */
int
GNUNET_CRYPTO_ecdsa_public_key_from_string (
  const char *enc,
  size_t enclen,
  struct GNUNET_CRYPTO_EcdsaPublicKey *pub)
{
  size_t keylen = (sizeof(struct GNUNET_CRYPTO_EcdsaPublicKey)) * 8;

  if (keylen % 5 > 0)
    keylen += 5 - keylen % 5;
  keylen /= 5;
  if (enclen != keylen)
    return GNUNET_SYSERR;

  if (GNUNET_OK !=
      GNUNET_STRINGS_string_to_data (enc,
                                     enclen,
                                     pub,
                                     sizeof(
                                       struct GNUNET_CRYPTO_EcdsaPublicKey)))
    return GNUNET_SYSERR;
  return GNUNET_OK;
}


/**
 * Convert a string representing a public key to a public key.
 *
 * @param enc encoded public key
 * @param enclen number of bytes in @a enc (without 0-terminator)
 * @param pub where to store the public key
 * @return #GNUNET_OK on success
 */
int
GNUNET_CRYPTO_eddsa_public_key_from_string (
  const char *enc,
  size_t enclen,
  struct GNUNET_CRYPTO_EddsaPublicKey *pub)
{
  size_t keylen = (sizeof(struct GNUNET_CRYPTO_EddsaPublicKey)) * 8;

  if (keylen % 5 > 0)
    keylen += 5 - keylen % 5;
  keylen /= 5;
  if (enclen != keylen)
    return GNUNET_SYSERR;

  if (GNUNET_OK !=
      GNUNET_STRINGS_string_to_data (enc,
                                     enclen,
                                     pub,
                                     sizeof(
                                       struct GNUNET_CRYPTO_EddsaPublicKey)))
    return GNUNET_SYSERR;
  return GNUNET_OK;
}


/**
 * Convert a string representing a private key to a private key.
 *
 * @param enc encoded public key
 * @param enclen number of bytes in @a enc (without 0-terminator)
 * @param priv where to store the private key
 * @return #GNUNET_OK on success
 */
int
GNUNET_CRYPTO_eddsa_private_key_from_string (
  const char *enc,
  size_t enclen,
  struct GNUNET_CRYPTO_EddsaPrivateKey *priv)
{
  size_t keylen = (sizeof(struct GNUNET_CRYPTO_EddsaPrivateKey)) * 8;

  if (keylen % 5 > 0)
    keylen += 5 - keylen % 5;
  keylen /= 5;
  if (enclen != keylen)
    return GNUNET_SYSERR;

  if (GNUNET_OK !=
      GNUNET_STRINGS_string_to_data (enc,
                                     enclen,
                                     priv,
                                     sizeof(
                                       struct GNUNET_CRYPTO_EddsaPrivateKey)))
    return GNUNET_SYSERR;
#if CRYPTO_BUG
  if (GNUNET_OK != check_eddsa_key (priv))
  {
    GNUNET_break (0);
    return GNUNET_OK;
  }
#endif
  return GNUNET_OK;
}


/**
 * @ingroup crypto
 * Clear memory that was used to store a private key.
 *
 * @param pk location of the key
 */
void
GNUNET_CRYPTO_ecdhe_key_clear (struct GNUNET_CRYPTO_EcdhePrivateKey *pk)
{
  memset (pk, 0, sizeof(struct GNUNET_CRYPTO_EcdhePrivateKey));
}


/**
 * @ingroup crypto
 * Clear memory that was used to store a private key.
 *
 * @param pk location of the key
 */
void
GNUNET_CRYPTO_ecdsa_key_clear (struct GNUNET_CRYPTO_EcdsaPrivateKey *pk)
{
  memset (pk, 0, sizeof(struct GNUNET_CRYPTO_EcdsaPrivateKey));
}


/**
 * @ingroup crypto
 * Clear memory that was used to store a private key.
 *
 * @param pk location of the key
 */
void
GNUNET_CRYPTO_eddsa_key_clear (struct GNUNET_CRYPTO_EddsaPrivateKey *pk)
{
  memset (pk, 0, sizeof(struct GNUNET_CRYPTO_EddsaPrivateKey));
}


/**
 * Create a new private key. Caller must free return value.
 *
 * @return fresh private key
 */
struct GNUNET_CRYPTO_EcdhePrivateKey *
GNUNET_CRYPTO_ecdhe_key_create ()
{
  struct GNUNET_CRYPTO_EcdhePrivateKey *priv;

  priv = GNUNET_new (struct GNUNET_CRYPTO_EcdhePrivateKey);
  if (GNUNET_OK != GNUNET_CRYPTO_ecdhe_key_create2 (priv))
  {
    GNUNET_free (priv);
    return NULL;
  }
  return priv;
}


/**
 * @ingroup crypto
 * Create a new private key.  Clear with #GNUNET_CRYPTO_ecdhe_key_clear().
 *
 * @param[out] pk set to fresh private key;
 * @return #GNUNET_OK on success, #GNUNET_SYSERR on failure
 */
int
GNUNET_CRYPTO_ecdhe_key_create2 (struct GNUNET_CRYPTO_EcdhePrivateKey *pk)
{
  gcry_sexp_t priv_sexp;
  gcry_sexp_t s_keyparam;
  gcry_mpi_t d;
  int rc;

  BENCHMARK_START (ecdhe_key_create);

  /* NOTE: For libgcrypt >= 1.7, we do not need the 'eddsa' flag here,
     but should also be harmless. For libgcrypt < 1.7, using 'eddsa'
     disables an expensive key testing routine. We do not want to run
     the expensive check for ECDHE, as we generate TONS of keys to
     use for a very short time. */
  if (0 != (rc = gcry_sexp_build (&s_keyparam,
                                  NULL,
                                  "(genkey(ecc(curve \"" CURVE "\")"
                                  "(flags eddsa no-keytest)))")))
  {
    LOG_GCRY (GNUNET_ERROR_TYPE_ERROR, "gcry_sexp_build", rc);
    return GNUNET_SYSERR;
  }
  if (0 != (rc = gcry_pk_genkey (&priv_sexp, s_keyparam)))
  {
    LOG_GCRY (GNUNET_ERROR_TYPE_ERROR, "gcry_pk_genkey", rc);
    gcry_sexp_release (s_keyparam);
    return GNUNET_SYSERR;
  }
  gcry_sexp_release (s_keyparam);
#if EXTRA_CHECKS
  if (0 != (rc = gcry_pk_testkey (priv_sexp)))
  {
    LOG_GCRY (GNUNET_ERROR_TYPE_ERROR, "gcry_pk_testkey", rc);
    gcry_sexp_release (priv_sexp);
    return GNUNET_SYSERR;
  }
#endif
  if (0 != (rc = key_from_sexp (&d, priv_sexp, "private-key", "d")))
  {
    LOG_GCRY (GNUNET_ERROR_TYPE_ERROR, "key_from_sexp", rc);
    gcry_sexp_release (priv_sexp);
    return GNUNET_SYSERR;
  }
  gcry_sexp_release (priv_sexp);
  GNUNET_CRYPTO_mpi_print_unsigned (pk->d, sizeof(pk->d), d);
  gcry_mpi_release (d);

  BENCHMARK_END (ecdhe_key_create);

  return GNUNET_OK;
}


/**
 * Create a new private key. Caller must free return value.
 *
 * @return fresh private key
 */
struct GNUNET_CRYPTO_EcdsaPrivateKey *
GNUNET_CRYPTO_ecdsa_key_create ()
{
  struct GNUNET_CRYPTO_EcdsaPrivateKey *priv;
  gcry_sexp_t priv_sexp;
  gcry_sexp_t s_keyparam;
  gcry_mpi_t d;
  int rc;

  BENCHMARK_START (ecdsa_key_create);

  if (0 != (rc = gcry_sexp_build (&s_keyparam,
                                  NULL,
                                  "(genkey(ecc(curve \"" CURVE "\")"
                                  "(flags)))")))
  {
    LOG_GCRY (GNUNET_ERROR_TYPE_ERROR, "gcry_sexp_build", rc);
    return NULL;
  }
  if (0 != (rc = gcry_pk_genkey (&priv_sexp, s_keyparam)))
  {
    LOG_GCRY (GNUNET_ERROR_TYPE_ERROR, "gcry_pk_genkey", rc);
    gcry_sexp_release (s_keyparam);
    return NULL;
  }
  gcry_sexp_release (s_keyparam);
#if EXTRA_CHECKS
  if (0 != (rc = gcry_pk_testkey (priv_sexp)))
  {
    LOG_GCRY (GNUNET_ERROR_TYPE_ERROR, "gcry_pk_testkey", rc);
    gcry_sexp_release (priv_sexp);
    return NULL;
  }
#endif
  if (0 != (rc = key_from_sexp (&d, priv_sexp, "private-key", "d")))
  {
    LOG_GCRY (GNUNET_ERROR_TYPE_ERROR, "key_from_sexp", rc);
    gcry_sexp_release (priv_sexp);
    return NULL;
  }
  gcry_sexp_release (priv_sexp);
  priv = GNUNET_new (struct GNUNET_CRYPTO_EcdsaPrivateKey);
  GNUNET_CRYPTO_mpi_print_unsigned (priv->d, sizeof(priv->d), d);
  gcry_mpi_release (d);

  BENCHMARK_END (ecdsa_key_create);

  return priv;
}

/**
 * Create a new private key. Caller must free return value.
 *
 * @return fresh private key
 */
struct GNUNET_CRYPTO_EddsaPrivateKey *
GNUNET_CRYPTO_eddsa_key_create ()
{
  struct GNUNET_CRYPTO_EddsaPrivateKey *priv;
  gcry_sexp_t priv_sexp;
  gcry_sexp_t s_keyparam;
  gcry_mpi_t d;
  int rc;

  BENCHMARK_START (eddsa_key_create);

#if CRYPTO_BUG
again:
#endif
  if (0 != (rc = gcry_sexp_build (&s_keyparam,
                                  NULL,
                                  "(genkey(ecc(curve \"" CURVE "\")"
                                  "(flags eddsa)))")))
  {
    LOG_GCRY (GNUNET_ERROR_TYPE_ERROR, "gcry_sexp_build", rc);
    return NULL;
  }
  if (0 != (rc = gcry_pk_genkey (&priv_sexp, s_keyparam)))
  {
    LOG_GCRY (GNUNET_ERROR_TYPE_ERROR, "gcry_pk_genkey", rc);
    gcry_sexp_release (s_keyparam);
    return NULL;
  }
  gcry_sexp_release (s_keyparam);
#if EXTRA_CHECKS
  if (0 != (rc = gcry_pk_testkey (priv_sexp)))
  {
    LOG_GCRY (GNUNET_ERROR_TYPE_ERROR, "gcry_pk_testkey", rc);
    gcry_sexp_release (priv_sexp);
    return NULL;
  }
#endif
  if (0 != (rc = key_from_sexp (&d, priv_sexp, "private-key", "d")))
  {
    LOG_GCRY (GNUNET_ERROR_TYPE_ERROR, "key_from_sexp", rc);
    gcry_sexp_release (priv_sexp);
    return NULL;
  }
  gcry_sexp_release (priv_sexp);
  priv = GNUNET_new (struct GNUNET_CRYPTO_EddsaPrivateKey);
  GNUNET_CRYPTO_mpi_print_unsigned (priv->d, sizeof(priv->d), d);
  gcry_mpi_release (d);

#if CRYPTO_BUG
  if (GNUNET_OK != check_eddsa_key (priv))
  {
    GNUNET_break (0);
    GNUNET_free (priv);
    goto again;
  }
#endif

  BENCHMARK_END (eddsa_key_create);

  return priv;
}


/**
 * Get the shared private key we use for anonymous users.
 *
 * @return "anonymous" private key
 */
const struct GNUNET_CRYPTO_EcdsaPrivateKey *
GNUNET_CRYPTO_ecdsa_key_get_anonymous ()
{
  /**
   * 'anonymous' pseudonym (global static, d=1, public key = G
   * (generator).
   */
  static struct GNUNET_CRYPTO_EcdsaPrivateKey anonymous;
  static int once;

  if (once)
    return &anonymous;
  GNUNET_CRYPTO_mpi_print_unsigned (anonymous.d,
                                    sizeof(anonymous.d),
                                    GCRYMPI_CONST_ONE);
  once = 1;
  return &anonymous;
}


/**
 * Convert the data specified in the given purpose argument to an
 * S-expression suitable for signature operations.
 *
 * @param purpose data to convert
 * @return converted s-expression
 */
static gcry_sexp_t
data_to_eddsa_value (const struct GNUNET_CRYPTO_EccSignaturePurpose *purpose)
{
  gcry_sexp_t data;
  int rc;

/* SEE #5398 */
#if 1
  struct GNUNET_HashCode hc;

  GNUNET_CRYPTO_hash (purpose, ntohl (purpose->size), &hc);
  if (0 != (rc = gcry_sexp_build (&data,
                                  NULL,
                                  "(data(flags eddsa)(hash-algo %s)(value %b))",
                                  "sha512",
                                  (int) sizeof(hc),
                                  &hc)))
  {
    LOG_GCRY (GNUNET_ERROR_TYPE_ERROR, "gcry_sexp_build", rc);
    return NULL;
  }
#else
  GNUNET_CRYPTO_hash (purpose, ntohl (purpose->size), &hc);
  if (0 != (rc = gcry_sexp_build (&data,
                                  NULL,
                                  "(data(flags eddsa)(hash-algo %s)(value %b))",
                                  "sha512",
                                  ntohl (purpose->size),
                                  purpose)))
  {
    LOG_GCRY (GNUNET_ERROR_TYPE_ERROR, "gcry_sexp_build", rc);
    return NULL;
  }
#endif
  return data;
}


/**
 * Convert the data specified in the given purpose argument to an
 * S-expression suitable for signature operations.
 *
 * @param purpose data to convert
 * @return converted s-expression
 */
static gcry_sexp_t
data_to_ecdsa_value (const struct GNUNET_CRYPTO_EccSignaturePurpose *purpose)
{
  gcry_sexp_t data;
  int rc;

/* See #5398 */
#if 1
  struct GNUNET_HashCode hc;

  GNUNET_CRYPTO_hash (purpose, ntohl (purpose->size), &hc);
  if (0 != (rc = gcry_sexp_build (&data,
                                  NULL,
                                  "(data(flags rfc6979)(hash %s %b))",
                                  "sha512",
                                  (int) sizeof(hc),
                                  &hc)))
  {
    LOG_GCRY (GNUNET_ERROR_TYPE_ERROR, "gcry_sexp_build", rc);
    return NULL;
  }
#else
  if (0 != (rc = gcry_sexp_build (&data,
                                  NULL,
                                  "(data(flags rfc6979)(hash %s %b))",
                                  "sha512",
                                  ntohl (purpose->size),
                                  purpose)))
  {
    LOG_GCRY (GNUNET_ERROR_TYPE_ERROR, "gcry_sexp_build", rc);
    return NULL;
  }
#endif
  return data;
}


/**
 * Sign a given block.
 *
 * @param priv private key to use for the signing
 * @param purpose what to sign (size, purpose)
 * @param sig where to write the signature
 * @return #GNUNET_SYSERR on error, #GNUNET_OK on success
 */
int
GNUNET_CRYPTO_ecdsa_sign (
  const struct GNUNET_CRYPTO_EcdsaPrivateKey *priv,
  const struct GNUNET_CRYPTO_EccSignaturePurpose *purpose,
  struct GNUNET_CRYPTO_EcdsaSignature *sig)
{
  gcry_sexp_t priv_sexp;
  gcry_sexp_t sig_sexp;
  gcry_sexp_t data;
  int rc;
  gcry_mpi_t rs[2];

  BENCHMARK_START (ecdsa_sign);

  priv_sexp = decode_private_ecdsa_key (priv);
  data = data_to_ecdsa_value (purpose);
  if (0 != (rc = gcry_pk_sign (&sig_sexp, data, priv_sexp)))
  {
    LOG (GNUNET_ERROR_TYPE_WARNING,
         _ ("ECC signing failed at %s:%d: %s\n"),
         __FILE__,
         __LINE__,
         gcry_strerror (rc));
    gcry_sexp_release (data);
    gcry_sexp_release (priv_sexp);
    return GNUNET_SYSERR;
  }
  gcry_sexp_release (priv_sexp);
  gcry_sexp_release (data);

  /* extract 'r' and 's' values from sexpression 'sig_sexp' and store in
     'signature' */
  if (0 != (rc = key_from_sexp (rs, sig_sexp, "sig-val", "rs")))
  {
    GNUNET_break (0);
    gcry_sexp_release (sig_sexp);
    return GNUNET_SYSERR;
  }
  gcry_sexp_release (sig_sexp);
  GNUNET_CRYPTO_mpi_print_unsigned (sig->r, sizeof(sig->r), rs[0]);
  GNUNET_CRYPTO_mpi_print_unsigned (sig->s, sizeof(sig->s), rs[1]);
  gcry_mpi_release (rs[0]);
  gcry_mpi_release (rs[1]);

  BENCHMARK_END (ecdsa_sign);

  return GNUNET_OK;
}


/**
 * Sign a given block.
 *
 * @param priv private key to use for the signing
 * @param purpose what to sign (size, purpose)
 * @param sig where to write the signature
 * @return #GNUNET_SYSERR on error, #GNUNET_OK on success
 */
int
GNUNET_CRYPTO_eddsa_sign (
  const struct GNUNET_CRYPTO_EddsaPrivateKey *priv,
  const struct GNUNET_CRYPTO_EccSignaturePurpose *purpose,
  struct GNUNET_CRYPTO_EddsaSignature *sig)
{
  gcry_sexp_t priv_sexp;
  gcry_sexp_t sig_sexp;
  gcry_sexp_t data;
  int rc;
  gcry_mpi_t rs[2];

  BENCHMARK_START (eddsa_sign);

  priv_sexp = decode_private_eddsa_key (priv);
  data = data_to_eddsa_value (purpose);
  if (0 != (rc = gcry_pk_sign (&sig_sexp, data, priv_sexp)))
  {
    LOG (GNUNET_ERROR_TYPE_WARNING,
         _ ("EdDSA signing failed at %s:%d: %s\n"),
         __FILE__,
         __LINE__,
         gcry_strerror (rc));
    gcry_sexp_release (data);
    gcry_sexp_release (priv_sexp);
    return GNUNET_SYSERR;
  }
  gcry_sexp_release (priv_sexp);
  gcry_sexp_release (data);

  /* extract 'r' and 's' values from sexpression 'sig_sexp' and store in
     'signature' */
  if (0 != (rc = key_from_sexp (rs, sig_sexp, "sig-val", "rs")))
  {
    GNUNET_break (0);
    gcry_sexp_release (sig_sexp);
    return GNUNET_SYSERR;
  }
  gcry_sexp_release (sig_sexp);
  GNUNET_CRYPTO_mpi_print_unsigned (sig->r, sizeof(sig->r), rs[0]);
  GNUNET_CRYPTO_mpi_print_unsigned (sig->s, sizeof(sig->s), rs[1]);
  gcry_mpi_release (rs[0]);
  gcry_mpi_release (rs[1]);

  BENCHMARK_END (eddsa_sign);

  return GNUNET_OK;
}


/**
 * Verify signature.
 *
 * @param purpose what is the purpose that the signature should have?
 * @param validate block to validate (size, purpose, data)
 * @param sig signature that is being validated
 * @param pub public key of the signer
 * @returns #GNUNET_OK if ok, #GNUNET_SYSERR if invalid
 */
int
GNUNET_CRYPTO_ecdsa_verify (
  uint32_t purpose,
  const struct GNUNET_CRYPTO_EccSignaturePurpose *validate,
  const struct GNUNET_CRYPTO_EcdsaSignature *sig,
  const struct GNUNET_CRYPTO_EcdsaPublicKey *pub)
{
  gcry_sexp_t data;
  gcry_sexp_t sig_sexpr;
  gcry_sexp_t pub_sexpr;
  int rc;

  BENCHMARK_START (ecdsa_verify);

  if (purpose != ntohl (validate->purpose))
    return GNUNET_SYSERR; /* purpose mismatch */

  /* build s-expression for signature */
  if (0 != (rc = gcry_sexp_build (&sig_sexpr,
                                  NULL,
                                  "(sig-val(ecdsa(r %b)(s %b)))",
                                  (int) sizeof(sig->r),
                                  sig->r,
                                  (int) sizeof(sig->s),
                                  sig->s)))
  {
    LOG_GCRY (GNUNET_ERROR_TYPE_ERROR, "gcry_sexp_build", rc);
    return GNUNET_SYSERR;
  }
  data = data_to_ecdsa_value (validate);
  if (0 != (rc = gcry_sexp_build (&pub_sexpr,
                                  NULL,
                                  "(public-key(ecc(curve " CURVE ")(q %b)))",
                                  (int) sizeof(pub->q_y),
                                  pub->q_y)))
  {
    gcry_sexp_release (data);
    gcry_sexp_release (sig_sexpr);
    return GNUNET_SYSERR;
  }
  rc = gcry_pk_verify (sig_sexpr, data, pub_sexpr);
  gcry_sexp_release (pub_sexpr);
  gcry_sexp_release (data);
  gcry_sexp_release (sig_sexpr);
  if (0 != rc)
  {
    LOG (GNUNET_ERROR_TYPE_INFO,
         _ ("ECDSA signature verification failed at %s:%d: %s\n"),
         __FILE__,
         __LINE__,
         gcry_strerror (rc));
    BENCHMARK_END (ecdsa_verify);
    return GNUNET_SYSERR;
  }
  BENCHMARK_END (ecdsa_verify);
  return GNUNET_OK;
}


/**
 * Verify signature.
 *
 * @param purpose what is the purpose that the signature should have?
 * @param validate block to validate (size, purpose, data)
 * @param sig signature that is being validated
 * @param pub public key of the signer
 * @returns #GNUNET_OK if ok, #GNUNET_SYSERR if invalid
 */
int
GNUNET_CRYPTO_eddsa_verify (
  uint32_t purpose,
  const struct GNUNET_CRYPTO_EccSignaturePurpose *validate,
  const struct GNUNET_CRYPTO_EddsaSignature *sig,
  const struct GNUNET_CRYPTO_EddsaPublicKey *pub)
{
  gcry_sexp_t data;
  gcry_sexp_t sig_sexpr;
  gcry_sexp_t pub_sexpr;
  int rc;

  BENCHMARK_START (eddsa_verify);

  if (purpose != ntohl (validate->purpose))
    return GNUNET_SYSERR; /* purpose mismatch */

  /* build s-expression for signature */
  if (0 != (rc = gcry_sexp_build (&sig_sexpr,
                                  NULL,
                                  "(sig-val(eddsa(r %b)(s %b)))",
                                  (int) sizeof(sig->r),
                                  sig->r,
                                  (int) sizeof(sig->s),
                                  sig->s)))
  {
    LOG_GCRY (GNUNET_ERROR_TYPE_ERROR, "gcry_sexp_build", rc);
    return GNUNET_SYSERR;
  }
  data = data_to_eddsa_value (validate);
  if (0 != (rc = gcry_sexp_build (&pub_sexpr,
                                  NULL,
                                  "(public-key(ecc(curve " CURVE
                                  ")(flags eddsa)(q %b)))",
                                  (int) sizeof(pub->q_y),
                                  pub->q_y)))
  {
    gcry_sexp_release (data);
    gcry_sexp_release (sig_sexpr);
    return GNUNET_SYSERR;
  }
  rc = gcry_pk_verify (sig_sexpr, data, pub_sexpr);
  gcry_sexp_release (pub_sexpr);
  gcry_sexp_release (data);
  gcry_sexp_release (sig_sexpr);
  if (0 != rc)
  {
    LOG (GNUNET_ERROR_TYPE_INFO,
         _ ("EdDSA signature verification of type %u failed at %s:%d: %s\n"),
         (unsigned int) purpose,
         __FILE__,
         __LINE__,
         gcry_strerror (rc));
    BENCHMARK_END (eddsa_verify);
    return GNUNET_SYSERR;
  }
  BENCHMARK_END (eddsa_verify);
  return GNUNET_OK;
}


/**
 * Derive key material from a public and a private ECDHE key.
 *
 * @param priv private key to use for the ECDH (x)
 * @param pub public key to use for the ECDH (yG)
 * @param key_material where to write the key material (xyG)
 * @return #GNUNET_SYSERR on error, #GNUNET_OK on success
 */
int
GNUNET_CRYPTO_ecc_ecdh (const struct GNUNET_CRYPTO_EcdhePrivateKey *priv,
                        const struct GNUNET_CRYPTO_EcdhePublicKey *pub,
                        struct GNUNET_HashCode *key_material)
{
  gcry_mpi_point_t result;
  gcry_mpi_point_t q;
  gcry_mpi_t d;
  gcry_ctx_t ctx;
  gcry_sexp_t pub_sexpr;
  gcry_mpi_t result_x;
  unsigned char xbuf[256 / 8];
  size_t rsize;

  BENCHMARK_START (ecc_ecdh);

  /* first, extract the q = dP value from the public key */
  if (0 != gcry_sexp_build (&pub_sexpr,
                            NULL,
                            "(public-key(ecc(curve " CURVE ")(q %b)))",
                            (int) sizeof(pub->q_y),
                            pub->q_y))
    return GNUNET_SYSERR;
  GNUNET_assert (0 == gcry_mpi_ec_new (&ctx, pub_sexpr, NULL));
  gcry_sexp_release (pub_sexpr);
  q = gcry_mpi_ec_get_point ("q", ctx, 0);

  /* second, extract the d value from our private key */
  GNUNET_CRYPTO_mpi_scan_unsigned (&d, priv->d, sizeof(priv->d));

  /* then call the 'multiply' function, to compute the product */
  result = gcry_mpi_point_new (0);
  gcry_mpi_ec_mul (result, d, q, ctx);
  gcry_mpi_point_release (q);
  gcry_mpi_release (d);

  /* finally, convert point to string for hashing */
  result_x = gcry_mpi_new (256);
  if (gcry_mpi_ec_get_affine (result_x, NULL, result, ctx))
  {
    LOG_GCRY (GNUNET_ERROR_TYPE_ERROR, "get_affine failed", 0);
    gcry_mpi_point_release (result);
    gcry_ctx_release (ctx);
    return GNUNET_SYSERR;
  }
  gcry_mpi_point_release (result);
  gcry_ctx_release (ctx);

  rsize = sizeof(xbuf);
  GNUNET_assert (! gcry_mpi_get_flag (result_x, GCRYMPI_FLAG_OPAQUE));
  /* result_x can be negative here, so we do not use 'GNUNET_CRYPTO_mpi_print_unsigned'
     as that does not include the sign bit; x should be a 255-bit
     value, so with the sign it should fit snugly into the 256-bit
     xbuf */
  GNUNET_assert (
    0 == gcry_mpi_print (GCRYMPI_FMT_STD, xbuf, rsize, &rsize, result_x));
  GNUNET_CRYPTO_hash (xbuf, rsize, key_material);
  gcry_mpi_release (result_x);
  BENCHMARK_END (ecc_ecdh);
  return GNUNET_OK;
}


/**
 * Derive the 'h' value for key derivation, where
 * 'h = H(l,P)'.
 *
 * @param pub public key for deriviation
 * @param label label for deriviation
 * @param context additional context to use for HKDF of 'h';
 *        typically the name of the subsystem/application
 * @return h value
 */
static gcry_mpi_t
derive_h (const struct GNUNET_CRYPTO_EcdsaPublicKey *pub,
          const char *label,
          const char *context)
{
  gcry_mpi_t h;
  struct GNUNET_HashCode hc;
  static const char *const salt = "key-derivation";

  GNUNET_CRYPTO_kdf (&hc,
                     sizeof(hc),
                     salt,
                     strlen (salt),
                     pub,
                     sizeof(*pub),
                     label,
                     strlen (label),
                     context,
                     strlen (context),
                     NULL,
                     0);
  GNUNET_CRYPTO_mpi_scan_unsigned (&h, (unsigned char *) &hc, sizeof(hc));
  return h;
}


/**
 * Derive a private key from a given private key and a label.
 * Essentially calculates a private key 'd = H(l,P) * x mod n'
 * where n is the size of the ECC group and P is the public
 * key associated with the private key 'd'.
 *
 * @param priv original private key
 * @param label label to use for key deriviation
 * @param context additional context to use for HKDF of 'h';
 *        typically the name of the subsystem/application
 * @return derived private key
 */
struct GNUNET_CRYPTO_EcdsaPrivateKey *
GNUNET_CRYPTO_ecdsa_private_key_derive (
  const struct GNUNET_CRYPTO_EcdsaPrivateKey *priv,
  const char *label,
  const char *context)
{
  struct GNUNET_CRYPTO_EcdsaPublicKey pub;
  struct GNUNET_CRYPTO_EcdsaPrivateKey *ret;
  gcry_mpi_t h;
  gcry_mpi_t x;
  gcry_mpi_t d;
  gcry_mpi_t n;
  gcry_ctx_t ctx;

  GNUNET_assert (0 == gcry_mpi_ec_new (&ctx, NULL, CURVE));

  n = gcry_mpi_ec_get_mpi ("n", ctx, 1);
  GNUNET_CRYPTO_ecdsa_key_get_public (priv, &pub);

  h = derive_h (&pub, label, context);
  GNUNET_CRYPTO_mpi_scan_unsigned (&x, priv->d, sizeof(priv->d));
  d = gcry_mpi_new (256);
  gcry_mpi_mulm (d, h, x, n);
  gcry_mpi_release (h);
  gcry_mpi_release (x);
  gcry_mpi_release (n);
  gcry_ctx_release (ctx);
  ret = GNUNET_new (struct GNUNET_CRYPTO_EcdsaPrivateKey);
  GNUNET_CRYPTO_mpi_print_unsigned (ret->d, sizeof(ret->d), d);
  gcry_mpi_release (d);
  return ret;
}


/**
 * Derive a public key from a given public key and a label.
 * Essentially calculates a public key 'V = H(l,P) * P'.
 *
 * @param pub original public key
 * @param label label to use for key derivation
 * @param context additional context to use for HKDF of 'h';
 *        typically the name of the subsystem/application
 * @param result where to write the derived public key
 */
void
GNUNET_CRYPTO_ecdsa_public_key_derive (
  const struct GNUNET_CRYPTO_EcdsaPublicKey *pub,
  const char *label,
  const char *context,
  struct GNUNET_CRYPTO_EcdsaPublicKey *result)
{
  gcry_ctx_t ctx;
  gcry_mpi_t q_y;
  gcry_mpi_t h;
  gcry_mpi_t n;
  gcry_mpi_t h_mod_n;
  gcry_mpi_point_t q;
  gcry_mpi_point_t v;

  GNUNET_assert (0 == gcry_mpi_ec_new (&ctx, NULL, CURVE));

  /* obtain point 'q' from original public key.  The provided 'q' is
     compressed thus we first store it in the context and then get it
     back as a (decompresssed) point.  */
  q_y = gcry_mpi_set_opaque_copy (NULL, pub->q_y, 8 * sizeof(pub->q_y));
  GNUNET_assert (NULL != q_y);
  GNUNET_assert (0 == gcry_mpi_ec_set_mpi ("q", q_y, ctx));
  gcry_mpi_release (q_y);
  q = gcry_mpi_ec_get_point ("q", ctx, 0);
  GNUNET_assert (q);

  /* calculate h_mod_n = h % n */
  h = derive_h (pub, label, context);
  n = gcry_mpi_ec_get_mpi ("n", ctx, 1);
  h_mod_n = gcry_mpi_new (256);
  gcry_mpi_mod (h_mod_n, h, n);
  /* calculate v = h_mod_n * q */
  v = gcry_mpi_point_new (0);
  gcry_mpi_ec_mul (v, h_mod_n, q, ctx);
  gcry_mpi_release (h_mod_n);
  gcry_mpi_release (h);
  gcry_mpi_release (n);
  gcry_mpi_point_release (q);

  /* convert point 'v' to public key that we return */
  GNUNET_assert (0 == gcry_mpi_ec_set_point ("q", v, ctx));
  gcry_mpi_point_release (v);
  q_y = gcry_mpi_ec_get_mpi ("q@eddsa", ctx, 0);
  GNUNET_assert (q_y);
  GNUNET_CRYPTO_mpi_print_unsigned (result->q_y, sizeof(result->q_y), q_y);
  gcry_mpi_release (q_y);
  gcry_ctx_release (ctx);
}


/**
 * Reverse the sequence of the bytes in @a buffer
 *
 * @param[in|out] buffer buffer to invert
 * @param length number of bytes in @a buffer
 */
static void
reverse_buffer (unsigned char *buffer, size_t length)
{
  unsigned char tmp;
  size_t i;

  for (i = 0; i < length / 2; i++)
  {
    tmp = buffer[i];
    buffer[i] = buffer[length - 1 - i];
    buffer[length - 1 - i] = tmp;
  }
}


/**
 * Convert the secret @a d of an EdDSA key to the
 * value that is actually used in the EdDSA computation.
 *
 * @param d secret input
 * @return value used for the calculation in EdDSA
 */
static gcry_mpi_t
eddsa_d_to_a (gcry_mpi_t d)
{
  unsigned char rawmpi[32]; /* 256-bit value */
  size_t rawmpilen;
  unsigned char digest[64]; /* 512-bit hash value */
  gcry_buffer_t hvec[2];
  unsigned int b;
  gcry_mpi_t a;

  b = 256 / 8; /* number of bytes in `d` */

  /* Note that we clear DIGEST so we can use it as input to left pad
     the key with zeroes for hashing.  */
  memset (digest, 0, sizeof digest);
  memset (hvec, 0, sizeof hvec);
  rawmpilen = sizeof(rawmpi);
  GNUNET_assert (
    0 == gcry_mpi_print (GCRYMPI_FMT_USG, rawmpi, rawmpilen, &rawmpilen, d));
  hvec[0].data = digest;
  hvec[0].off = 0;
  hvec[0].len = b > rawmpilen ? (b - rawmpilen) : 0;
  hvec[1].data = rawmpi;
  hvec[1].off = 0;
  hvec[1].len = rawmpilen;
  GNUNET_assert (
    0 == gcry_md_hash_buffers (GCRY_MD_SHA512, 0 /* flags */, digest, hvec, 2));
  /* Compute the A value.  */
  reverse_buffer (digest, 32);  /* Only the first half of the hash.  */
  digest[0] = (digest[0] & 0x7f) | 0x40;
  digest[31] &= 0xf8;

  GNUNET_CRYPTO_mpi_scan_unsigned (&a, digest, 32);
  return a;
}


/**
 * Take point from ECDH and convert it to key material.
 *
 * @param result point from ECDH
 * @param ctx ECC context
 * @param key_material[out] set to derived key material
 * @return #GNUNET_OK on success
 */
static int
point_to_hash (gcry_mpi_point_t result,
               gcry_ctx_t ctx,
               struct GNUNET_HashCode *key_material)
{
  gcry_mpi_t result_x;
  unsigned char xbuf[256 / 8];
  size_t rsize;

  /* finally, convert point to string for hashing */
  result_x = gcry_mpi_new (256);
  if (gcry_mpi_ec_get_affine (result_x, NULL, result, ctx))
  {
    LOG_GCRY (GNUNET_ERROR_TYPE_ERROR, "get_affine failed", 0);
    return GNUNET_SYSERR;
  }

  rsize = sizeof(xbuf);
  GNUNET_assert (! gcry_mpi_get_flag (result_x, GCRYMPI_FLAG_OPAQUE));
  /* result_x can be negative here, so we do not use 'GNUNET_CRYPTO_mpi_print_unsigned'
     as that does not include the sign bit; x should be a 255-bit
     value, so with the sign it should fit snugly into the 256-bit
     xbuf */
  GNUNET_assert (
    0 == gcry_mpi_print (GCRYMPI_FMT_STD, xbuf, rsize, &rsize, result_x));
  GNUNET_CRYPTO_hash (xbuf, rsize, key_material);
  gcry_mpi_release (result_x);
  return GNUNET_OK;
}


/**
 * @ingroup crypto
 * Derive key material from a ECDH public key and a private EdDSA key.
 * Dual to #GNUNET_CRRYPTO_ecdh_eddsa.
 *
 * @param priv private key from EdDSA to use for the ECDH (x)
 * @param pub public key to use for the ECDH (yG)
 * @param key_material where to write the key material H(h(x)yG)
 * @return #GNUNET_SYSERR on error, #GNUNET_OK on success
 */
int
GNUNET_CRYPTO_eddsa_ecdh (const struct GNUNET_CRYPTO_EddsaPrivateKey *priv,
                          const struct GNUNET_CRYPTO_EcdhePublicKey *pub,
                          struct GNUNET_HashCode *key_material)
{
  gcry_mpi_point_t result;
  gcry_mpi_point_t q;
  gcry_mpi_t d;
  gcry_mpi_t a;
  gcry_ctx_t ctx;
  gcry_sexp_t pub_sexpr;
  int ret;

  BENCHMARK_START (eddsa_ecdh);

  /* first, extract the q = dP value from the public key */
  if (0 != gcry_sexp_build (&pub_sexpr,
                            NULL,
                            "(public-key(ecc(curve " CURVE ")(q %b)))",
                            (int) sizeof(pub->q_y),
                            pub->q_y))
    return GNUNET_SYSERR;
  GNUNET_assert (0 == gcry_mpi_ec_new (&ctx, pub_sexpr, NULL));
  gcry_sexp_release (pub_sexpr);
  q = gcry_mpi_ec_get_point ("q", ctx, 0);

  /* second, extract the d value from our private key */
  GNUNET_CRYPTO_mpi_scan_unsigned (&d, priv->d, sizeof(priv->d));

  /* NOW, because this is EdDSA, HASH 'd' first! */
  a = eddsa_d_to_a (d);
  gcry_mpi_release (d);

  /* then call the 'multiply' function, to compute the product */
  result = gcry_mpi_point_new (0);
  gcry_mpi_ec_mul (result, a, q, ctx);
  gcry_mpi_point_release (q);
  gcry_mpi_release (a);

  ret = point_to_hash (result, ctx, key_material);
  gcry_mpi_point_release (result);
  gcry_ctx_release (ctx);
  BENCHMARK_END (eddsa_ecdh);
  return ret;
}


/**
 * @ingroup crypto
 * Derive key material from a ECDH public key and a private ECDSA key.
 * Dual to #GNUNET_CRRYPTO_ecdh_eddsa.
 *
 * @param priv private key from ECDSA to use for the ECDH (x)
 * @param pub public key to use for the ECDH (yG)
 * @param key_material where to write the key material H(h(x)yG)
 * @return #GNUNET_SYSERR on error, #GNUNET_OK on success
 */
int
GNUNET_CRYPTO_ecdsa_ecdh (const struct GNUNET_CRYPTO_EcdsaPrivateKey *priv,
                          const struct GNUNET_CRYPTO_EcdhePublicKey *pub,
                          struct GNUNET_HashCode *key_material)
{
  gcry_mpi_point_t result;
  gcry_mpi_point_t q;
  gcry_mpi_t d;
  gcry_ctx_t ctx;
  gcry_sexp_t pub_sexpr;
  int ret;

  BENCHMARK_START (ecdsa_ecdh);

  /* first, extract the q = dP value from the public key */
  if (0 != gcry_sexp_build (&pub_sexpr,
                            NULL,
                            "(public-key(ecc(curve " CURVE ")(q %b)))",
                            (int) sizeof(pub->q_y),
                            pub->q_y))
    return GNUNET_SYSERR;
  GNUNET_assert (0 == gcry_mpi_ec_new (&ctx, pub_sexpr, NULL));
  gcry_sexp_release (pub_sexpr);
  q = gcry_mpi_ec_get_point ("q", ctx, 0);

  /* second, extract the d value from our private key */
  GNUNET_CRYPTO_mpi_scan_unsigned (&d, priv->d, sizeof(priv->d));

  /* then call the 'multiply' function, to compute the product */
  result = gcry_mpi_point_new (0);
  gcry_mpi_ec_mul (result, d, q, ctx);
  gcry_mpi_point_release (q);
  gcry_mpi_release (d);

  /* finally, convert point to string for hashing */
  ret = point_to_hash (result, ctx, key_material);
  gcry_mpi_point_release (result);
  gcry_ctx_release (ctx);
  BENCHMARK_END (ecdsa_ecdh);
  return ret;
}


/**
 * @ingroup crypto
 * Derive key material from a EdDSA public key and a private ECDH key.
 * Dual to #GNUNET_CRRYPTO_eddsa_ecdh.
 *
 * @param priv private key to use for the ECDH (y)
 * @param pub public key from EdDSA to use for the ECDH (X=h(x)G)
 * @param key_material where to write the key material H(yX)=H(h(x)yG)
 * @return #GNUNET_SYSERR on error, #GNUNET_OK on success
 */
int
GNUNET_CRYPTO_ecdh_eddsa (const struct GNUNET_CRYPTO_EcdhePrivateKey *priv,
                          const struct GNUNET_CRYPTO_EddsaPublicKey *pub,
                          struct GNUNET_HashCode *key_material)
{
  gcry_mpi_point_t result;
  gcry_mpi_point_t q;
  gcry_mpi_t d;
  gcry_ctx_t ctx;
  gcry_sexp_t pub_sexpr;
  int ret;

  BENCHMARK_START (ecdh_eddsa);

  /* first, extract the q = dP value from the public key */
  if (0 != gcry_sexp_build (&pub_sexpr,
                            NULL,
                            "(public-key(ecc(curve " CURVE ")(q %b)))",
                            (int) sizeof(pub->q_y),
                            pub->q_y))
    return GNUNET_SYSERR;
  GNUNET_assert (0 == gcry_mpi_ec_new (&ctx, pub_sexpr, NULL));
  gcry_sexp_release (pub_sexpr);
  q = gcry_mpi_ec_get_point ("q", ctx, 0);

  /* second, extract the d value from our private key */
  GNUNET_CRYPTO_mpi_scan_unsigned (&d, priv->d, sizeof(priv->d));

  /* then call the 'multiply' function, to compute the product */
  result = gcry_mpi_point_new (0);
  gcry_mpi_ec_mul (result, d, q, ctx);
  gcry_mpi_point_release (q);
  gcry_mpi_release (d);

  /* finally, convert point to string for hashing */
  ret = point_to_hash (result, ctx, key_material);
  gcry_mpi_point_release (result);
  gcry_ctx_release (ctx);
  BENCHMARK_END (ecdh_eddsa);
  return ret;
}

/**
 * @ingroup crypto
 * Derive key material from a ECDSA public key and a private ECDH key.
 * Dual to #GNUNET_CRRYPTO_eddsa_ecdh.
 *
 * @param priv private key to use for the ECDH (y)
 * @param pub public key from ECDSA to use for the ECDH (X=h(x)G)
 * @param key_material where to write the key material H(yX)=H(h(x)yG)
 * @return #GNUNET_SYSERR on error, #GNUNET_OK on success
 */
int
GNUNET_CRYPTO_ecdh_ecdsa (const struct GNUNET_CRYPTO_EcdhePrivateKey *priv,
                          const struct GNUNET_CRYPTO_EcdsaPublicKey *pub,
                          struct GNUNET_HashCode *key_material)
{
  return GNUNET_CRYPTO_ecdh_eddsa (priv,
                                   (const struct GNUNET_CRYPTO_EddsaPublicKey *)
                                   pub,
                                   key_material);
}

/* end of crypto_ecc.c */