crypto_ecc.c File Reference

public key cryptography (ECC) with libgcrypt More...

#include "platform.h"
#include <gcrypt.h>
#include <sodium.h>
#include "gnunet_crypto_lib.h"
#include "gnunet_strings_lib.h"
#include "benchmark.h"

Include dependency graph for crypto_ecc.c:

Go to the source code of this file.

Macros
#define	EXTRA_CHECKS   0
#define	CURVE   "Ed25519"
	IMPLEMENTATION NOTICE: More...
#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)
#define	LOG_GCRY(level, cmd, rc)
	Log an error message at log-level 'level' that indicates a failure of the command 'cmd' with the message given by gcry_strerror(rc). More...

Functions
static int	key_from_sexp (gcry_mpi_t *array, gcry_sexp_t sexp, const char *topname, const char *elems)
	Extract values from an S-expression. More...
static gcry_sexp_t	decode_private_ecdsa_key (const struct GNUNET_CRYPTO_EcdsaPrivateKey *priv)
	Convert the given private key from the network format to the S-expression that can be used by libgcrypt. More...
void	GNUNET_CRYPTO_ecdsa_key_get_public (const struct GNUNET_CRYPTO_EcdsaPrivateKey *priv, struct GNUNET_CRYPTO_EcdsaPublicKey *pub)
	Extract the public key for the given private key. More...
void	GNUNET_CRYPTO_eddsa_key_get_public (const struct GNUNET_CRYPTO_EddsaPrivateKey *priv, struct GNUNET_CRYPTO_EddsaPublicKey *pub)
	Extract the public key for the given private key. More...
void	GNUNET_CRYPTO_ecdhe_key_get_public (const struct GNUNET_CRYPTO_EcdhePrivateKey *priv, struct GNUNET_CRYPTO_EcdhePublicKey *pub)
	Extract the public key for the given private key. More...
char *	GNUNET_CRYPTO_ecdsa_public_key_to_string (const struct GNUNET_CRYPTO_EcdsaPublicKey *pub)
	Convert a public key to a string. More...
char *	GNUNET_CRYPTO_eddsa_public_key_to_string (const struct GNUNET_CRYPTO_EddsaPublicKey *pub)
	Convert a public key to a string. More...
char *	GNUNET_CRYPTO_eddsa_private_key_to_string (const struct GNUNET_CRYPTO_EddsaPrivateKey *priv)
	Convert a private key to a string. More...
char *	GNUNET_CRYPTO_ecdsa_private_key_to_string (const struct GNUNET_CRYPTO_EcdsaPrivateKey *priv)
	Convert a private key to a string. More...
enum GNUNET_GenericReturnValue	GNUNET_CRYPTO_ecdsa_public_key_from_string (const char *enc, size_t enclen, struct GNUNET_CRYPTO_EcdsaPublicKey *pub)
	Convert a string representing a public key to a public key. More...
enum GNUNET_GenericReturnValue	GNUNET_CRYPTO_eddsa_public_key_from_string (const char *enc, size_t enclen, struct GNUNET_CRYPTO_EddsaPublicKey *pub)
	Convert a string representing a public key to a public key. More...
enum GNUNET_GenericReturnValue	GNUNET_CRYPTO_eddsa_private_key_from_string (const char *enc, size_t enclen, struct GNUNET_CRYPTO_EddsaPrivateKey *priv)
	Convert a string representing a private key to a private key. More...
void	GNUNET_CRYPTO_ecdhe_key_clear (struct GNUNET_CRYPTO_EcdhePrivateKey *pk)
	Clear memory that was used to store a private key. More...
void	GNUNET_CRYPTO_ecdsa_key_clear (struct GNUNET_CRYPTO_EcdsaPrivateKey *pk)
	Clear memory that was used to store a private key. More...
void	GNUNET_CRYPTO_eddsa_key_clear (struct GNUNET_CRYPTO_EddsaPrivateKey *pk)
	Clear memory that was used to store a private key. More...
void	GNUNET_CRYPTO_ecdhe_key_create (struct GNUNET_CRYPTO_EcdhePrivateKey *pk)
	Create a new private key. More...
void	GNUNET_CRYPTO_ecdsa_key_create (struct GNUNET_CRYPTO_EcdsaPrivateKey *pk)
	Create a new private key. More...
void	GNUNET_CRYPTO_eddsa_key_create (struct GNUNET_CRYPTO_EddsaPrivateKey *pk)
	Create a new private key. More...
const struct GNUNET_CRYPTO_EcdsaPrivateKey *	GNUNET_CRYPTO_ecdsa_key_get_anonymous ()
	Get the shared private key we use for anonymous users. More...
static gcry_sexp_t	data_to_ecdsa_value (const struct GNUNET_CRYPTO_EccSignaturePurpose *purpose)
	Convert the data specified in the given purpose argument to an S-expression suitable for signature operations. More...
enum GNUNET_GenericReturnValue	GNUNET_CRYPTO_ecdsa_sign_ (const struct GNUNET_CRYPTO_EcdsaPrivateKey *priv, const struct GNUNET_CRYPTO_EccSignaturePurpose *purpose, struct GNUNET_CRYPTO_EcdsaSignature *sig)
	ECDSA Sign a given block. More...
enum GNUNET_GenericReturnValue	GNUNET_CRYPTO_eddsa_sign_ (const struct GNUNET_CRYPTO_EddsaPrivateKey *priv, const struct GNUNET_CRYPTO_EccSignaturePurpose *purpose, struct GNUNET_CRYPTO_EddsaSignature *sig)
	EdDSA sign a given block. More...
enum GNUNET_GenericReturnValue	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)
	Verify ECDSA signature. More...
enum GNUNET_GenericReturnValue	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)
	Verify EdDSA signature. More...
enum GNUNET_GenericReturnValue	GNUNET_CRYPTO_ecc_ecdh (const struct GNUNET_CRYPTO_EcdhePrivateKey *priv, const struct GNUNET_CRYPTO_EcdhePublicKey *pub, struct GNUNET_HashCode *key_material)
	Derive key material from a public and a private ECC key. More...
enum GNUNET_GenericReturnValue	GNUNET_CRYPTO_eddsa_ecdh (const struct GNUNET_CRYPTO_EddsaPrivateKey *priv, const struct GNUNET_CRYPTO_EcdhePublicKey *pub, struct GNUNET_HashCode *key_material)
	Derive key material from a ECDH public key and a private EdDSA key. More...
enum GNUNET_GenericReturnValue	GNUNET_CRYPTO_ecdsa_ecdh (const struct GNUNET_CRYPTO_EcdsaPrivateKey *priv, const struct GNUNET_CRYPTO_EcdhePublicKey *pub, struct GNUNET_HashCode *key_material)
	Derive key material from a ECDH public key and a private ECDSA key. More...
enum GNUNET_GenericReturnValue	GNUNET_CRYPTO_ecdh_eddsa (const struct GNUNET_CRYPTO_EcdhePrivateKey *priv, const struct GNUNET_CRYPTO_EddsaPublicKey *pub, struct GNUNET_HashCode *key_material)
	Derive key material from a EdDSA public key and a private ECDH key. More...
enum GNUNET_GenericReturnValue	GNUNET_CRYPTO_ecdh_ecdsa (const struct GNUNET_CRYPTO_EcdhePrivateKey *priv, const struct GNUNET_CRYPTO_EcdsaPublicKey *pub, struct GNUNET_HashCode *key_material)
	Derive key material from a EcDSA public key and a private ECDH key. More...

Detailed Description

public key cryptography (ECC) with libgcrypt

Author

Christian Grothoff

Florian Dold

Definition in file crypto_ecc.c.

Macro Definition Documentation

EXTRA_CHECKS

#define EXTRA_CHECKS   0

Definition at line 34 of file crypto_ecc.c.

CURVE

#define CURVE   "Ed25519"

IMPLEMENTATION NOTICE:

ECDSA: We use a non-standard curve for ECDSA: Ed25519. For performance reasons, we use cryptographic operations from libsodium wherever we can get away with it, even though libsodium itself does not support ECDSA. This is why the sign and verifiy functionality from libgcrypt is required and used.

EdDSA: We use a standard EdDSA construction. (We still use libgcrypt for hashing and RNG, but not EC)

ECDHE: For both EdDSA and ECDSA keys, we use libsodium for ECDHE due to performance benefits over libgcrypt. 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.

Definition at line 59 of file crypto_ecc.c.

Referenced by decode_private_ecdsa_key(), and GNUNET_CRYPTO_ecdsa_verify_().

LOG

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

Definition at line 61 of file crypto_ecc.c.

Referenced by GNUNET_CRYPTO_ecdsa_sign_(), and GNUNET_CRYPTO_ecdsa_verify_().

LOG_STRERROR

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

Definition at line 63 of file crypto_ecc.c.

LOG_STRERROR_FILE

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

Definition at line 66 of file crypto_ecc.c.

LOG_GCRY

#define LOG_GCRY	(		level,
			cmd,
			rc
	)

Value:

do                                                  \
  {                                                   \
    LOG (level,                                       \
         _ ("`%s' failed at %s:%d with error: %s\n"), \
         cmd,                                         \
         __FILE__,                                    \
         __LINE__,                                    \
         gcry_strerror (rc));                         \
  } while (0)

Log an error message at log-level 'level' that indicates a failure of the command 'cmd' with the message given by gcry_strerror(rc).

Definition at line 74 of file crypto_ecc.c.

Referenced by data_to_ecdsa_value(), decode_private_ecdsa_key(), and GNUNET_CRYPTO_ecdsa_verify_().

Function Documentation

key_from_sexp()

static int key_from_sexp ( gcry_mpi_t *  array, gcry_sexp_t  sexp, const char *  topname, const char *  elems  )

static

Extract values from an S-expression.

Parameters

array	where to store the result(s)
sexp	S-expression to parse
topname	top-level name in the S-expression that is of interest
elems	names of the elements to extract

Returns

0 on success

Definition at line 96 of file crypto_ecc.c.

References list.

Referenced by GNUNET_CRYPTO_ecdsa_sign_().

{
  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;
}

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decode_private_ecdsa_key()

static gcry_sexp_t decode_private_ecdsa_key ( const struct GNUNET_CRYPTO_EcdsaPrivateKey *  priv )

static

Convert the given private key from the network format to the S-expression that can be used by libgcrypt.

Parameters

priv	private key to decode

Returns

NULL on error

Definition at line 154 of file crypto_ecc.c.

References CURVE, GNUNET_CRYPTO_EcdsaPrivateKey::d, GNUNET_assert, GNUNET_ERROR_TYPE_ERROR, LOG_GCRY, and result.

Referenced by GNUNET_CRYPTO_ecdsa_sign_().

{
  gcry_sexp_t result;
  int rc;
  uint8_t d[32];

  for (size_t i = 0; i<32; i++)
    d[i] = priv->d[31 - i];

  rc = gcry_sexp_build (&result,
                        NULL,
                        "(private-key(ecc(curve \"" CURVE "\")"
                        "(d %b)))",
                        32,
                        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;
}

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GNUNET_CRYPTO_ecdsa_public_key_to_string()

char* GNUNET_CRYPTO_ecdsa_public_key_to_string

(

const struct GNUNET_CRYPTO_EcdsaPublicKey *

pub

)

Convert a public key to a string.

Parameters

pub	key to convert

Returns

string representing pub

Definition at line 224 of file crypto_ecc.c.

References end, GNUNET_free, GNUNET_malloc, and GNUNET_STRINGS_data_to_string().

Referenced by abd_value_to_string(), delegation_chain_fw_resolution_start(), forward_resolution(), get_ego(), GNUNET_ABD_delegate_to_string(), handle_intermediate_result(), handle_verify_result(), print_deleset(), and store_cb().

{
  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;
}

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GNUNET_CRYPTO_eddsa_public_key_to_string()

char* GNUNET_CRYPTO_eddsa_public_key_to_string

(

const struct GNUNET_CRYPTO_EddsaPublicKey *

pub

)

Convert a public key to a string.

Parameters

pub	key to convert

Returns

string representing pub

Definition at line 251 of file crypto_ecc.c.

References end, GNUNET_free, GNUNET_malloc, and GNUNET_STRINGS_data_to_string().

Referenced by conversation_value_to_string(), create_keys(), GCP_2s(), GNUNET_FRIENDS_write(), GNUNET_HELLO_compose_uri(), GNUNET_i2s(), GNUNET_i2s2(), GNUNET_i2s_full(), main(), print_key(), run(), and uri_loc_to_string().

{
  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;
}

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GNUNET_CRYPTO_eddsa_private_key_to_string()

char* GNUNET_CRYPTO_eddsa_private_key_to_string

(

const struct GNUNET_CRYPTO_EddsaPrivateKey *

priv

)

Convert a private key to a string.

Parameters

priv	key to convert

Returns

string representing pub

Definition at line 278 of file crypto_ecc.c.

References end, GNUNET_free, GNUNET_malloc, and GNUNET_STRINGS_data_to_string().

Referenced by run().

{
  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;
}

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GNUNET_CRYPTO_ecdsa_private_key_to_string()

char* GNUNET_CRYPTO_ecdsa_private_key_to_string

(

const struct GNUNET_CRYPTO_EcdsaPrivateKey *

priv

)

Convert a private key to a string.

Parameters

priv	key to convert

Returns

string representing priv

Definition at line 305 of file crypto_ecc.c.

References end, GNUNET_free, GNUNET_malloc, and GNUNET_STRINGS_data_to_string().

{
  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;
}

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GNUNET_CRYPTO_ecdsa_public_key_from_string()

enum GNUNET_GenericReturnValue GNUNET_CRYPTO_ecdsa_public_key_from_string	(	const char *	enc,
		size_t	enclen,
		struct GNUNET_CRYPTO_EcdsaPublicKey *	pub
	)

Convert a string representing a public key to a public key.

Parameters

enc	encoded public key
enclen	number of bytes in enc (without 0-terminator)
pub	where to store the public key

Returns

GNUNET_OK on success

Definition at line 332 of file crypto_ecc.c.

References GNUNET_OK, GNUNET_STRINGS_string_to_data(), and GNUNET_SYSERR.

Referenced by abd_string_to_value(), GNUNET_ABD_delegate_from_string(), identity_cb(), run(), and sign_cb().

{
  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;
}

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GNUNET_CRYPTO_eddsa_public_key_from_string()

enum GNUNET_GenericReturnValue GNUNET_CRYPTO_eddsa_public_key_from_string	(	const char *	enc,
		size_t	enclen,
		struct GNUNET_CRYPTO_EddsaPublicKey *	pub
	)

Convert a string representing a public key to a public key.

Parameters

enc	encoded public key
enclen	number of bytes in enc (without 0-terminator)
pub	where to store the public key

Returns

GNUNET_OK on success

Definition at line 357 of file crypto_ecc.c.

References GNUNET_OK, GNUNET_STRINGS_string_to_data(), and GNUNET_SYSERR.

Referenced by blacklist_cfg_iter(), connect_peers_run(), conversation_string_to_value(), create_keys(), gns_string_to_value(), GNUNET_FRIENDS_parse(), hosts_directory_scan_callback(), on_identity(), run(), s2i_full(), server_parse_url(), show_peer(), and uri_loc_parse().

{
  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;
}

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GNUNET_CRYPTO_eddsa_private_key_from_string()

enum GNUNET_GenericReturnValue GNUNET_CRYPTO_eddsa_private_key_from_string	(	const char *	enc,
		size_t	enclen,
		struct GNUNET_CRYPTO_EddsaPrivateKey *	pub
	)

Convert a string representing a private key to a private key.

Parameters

enc	encoded public key
enclen	number of bytes in enc (without 0-terminator)
priv	where to store the private key

Returns

GNUNET_OK on success

Definition at line 382 of file crypto_ecc.c.

References GNUNET_break, GNUNET_OK, GNUNET_STRINGS_string_to_data(), and GNUNET_SYSERR.

{
  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;
}

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data_to_ecdsa_value()

static gcry_sexp_t data_to_ecdsa_value ( const struct GNUNET_CRYPTO_EccSignaturePurpose *  purpose )

static

Convert the data specified in the given purpose argument to an S-expression suitable for signature operations.

Parameters

purpose

data to convert

Returns

converted s-expression

Definition at line 512 of file crypto_ecc.c.

References data, GNUNET_CRYPTO_hash(), GNUNET_ERROR_TYPE_ERROR, LOG_GCRY, and GNUNET_CRYPTO_EccSignaturePurpose::size.

Referenced by GNUNET_CRYPTO_ecdsa_sign_(), and GNUNET_CRYPTO_ecdsa_verify_().

{
  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;
}

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