libbrandt/crypto.c

/* This file is part of libbrandt.
 * Copyright (C) 2016 GNUnet e.V.
 *
 * libbrandt 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 of the License, or (at your option) any later
 * version.
 *
 * libbrandt 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
 * libbrandt.  If not, see <http://www.gnu.org/licenses/>.
 */

/**
 * @file crypto.c
 * @brief Implementation of the crypto primitives.
 */

#include <arpa/inet.h>

#include "crypto.h"
#include "util.h"

#define CURVE "Ed25519"

struct brandt_ec_skey {
	unsigned char d[256 / 8];
};

struct brandt_ec_pkey {
	unsigned char q_y[256 / 8];
};

gcry_ctx_t       ec_ctx;
gcry_mpi_point_t ec_gen;
gcry_mpi_point_t ec_zero;
gcry_mpi_t       ec_n;

/**
 * brandt_crypto_init
 *
 *
 */
void
brandt_crypto_init ()
{
	gcry_error_t rc;

	rc = gcry_mpi_ec_new (&ec_ctx, NULL, CURVE);
	brandt_assert_gpgerr (rc);

	ec_gen = gcry_mpi_ec_get_point ("g", ec_ctx, 0);
	brandt_assert (NULL != ec_gen);

	ec_zero = gcry_mpi_point_new (0);
	brandt_assert (NULL != ec_zero);
	gcry_mpi_ec_sub (ec_zero, ec_gen, ec_gen, ec_ctx);

	ec_n = gcry_mpi_ec_get_mpi ("n", ec_ctx, 1);
	brandt_assert (NULL != ec_n);
}


/* --- RANDOM --- */

void
brandt_rand_poll ()
{
	static unsigned char rand_amount = 255;

	if (!(rand_amount--))
		gcry_fast_random_poll ();
}


/* --- HASHING --- */

/**
 * Hash block of given size.
 *
 * @param block the data to #brandt_hash, length is given as a second argument
 * @param size the length of the data to #brandt_hash in @a block
 * @param ret pointer to where to write the hashcode
 */
void
brandt_hash (const void *block, size_t size, struct brandt_hash_code *ret)
{
	gcry_md_hash_buffer (GCRY_MD_SHA512, ret, block, size);
}


/* --- MPI --- */

/**
 * If target != size, move @a target bytes to the end of the size-sized
 * buffer and zero out the first @a target - @a size bytes.
 *
 * @param buf original buffer
 * @param size number of bytes in @a buf
 * @param target target size of the buffer
 */
static void
adjust (void *buf, size_t size, size_t target)
{
	char *p = buf;

	if (size < target)
	{
		memmove (&p[target - size], buf, size);
		memset (buf, 0, target - size);
	}
}


/**
 * Output the given MPI value to the given buffer in
 * network byte order.
 * The MPI @a val may not be negative.
 *
 * @param buf where to output to
 * @param size number of bytes in @a buf
 * @param val value to write to @a buf
 */
void
brandt_mpi_print_unsigned (void *buf, size_t size, gcry_mpi_t val)
{
	size_t       rsize;
	gcry_error_t rc;

	if (gcry_mpi_get_flag (val, GCRYMPI_FLAG_OPAQUE))
	{
		/* Store opaque MPIs left aligned into the buffer.  */
		unsigned int nbits;
		const void   *p;

		p = gcry_mpi_get_opaque (val, &nbits);
		brandt_assert (NULL != p);
		rsize = (nbits + 7) / 8;
		if (rsize > size)
			rsize = size;
		memcpy (buf, p, rsize);
		if (rsize < size)
			memset (((char *)buf) + rsize, 0, size - rsize);
	}
	else
	{
		/* Store regular MPIs as unsigned integers right aligned into the buffer. */
		rsize = size;
		rc = gcry_mpi_print (GCRYMPI_FMT_USG, buf, rsize, &rsize, val);
		brandt_assert_gpgerr (rc);
		adjust (buf, rsize, size);
	}
}


/**
 * Convert data buffer into MPI value.
 * The buffer is interpreted as network
 * byte order, unsigned integer.
 *
 * @param result where to store MPI value (allocated)
 * @param data raw data (GCRYMPI_FMT_USG)
 * @param size number of bytes in @a data
 */
void
brandt_mpi_scan_unsigned (gcry_mpi_t *result, const void *data, size_t size)
{
	gcry_error_t rc;

	rc = gcry_mpi_scan (result, GCRYMPI_FMT_USG, data, size, &size);
	brandt_assert_gpgerr (rc);
}


//gcry_mpi_point_t
//deserialize_point(const struct brandt_point* data, const int len)
//{
//	gcry_sexp_t s;
//	gcry_ctx_t ctx;
//	gcry_mpi_point_t ret;
//	gcry_error_t rc;
//
//	rc = gcry_sexp_build(&s, NULL, "(public-key(ecc(curve " CURVE ")(q %b)))",
//						 len, data);
//	brandt_assert_gpgerr(rc);
//
//	rc = gcry_mpi_ec_new(&ctx, s, NULL);
//	brandt_assert_gpgerr(rc);
//	gcry_sexp_release(s);
//
//	ret = gcry_mpi_ec_get_point("q", ctx, 0);
//	brandt_assert(ret);
//	gcry_ctx_release(ctx);
//	return ret;
//}


/* --- EC --- */

/**
 * brandt_ec_skey_create
 *
 * @param[out] skey where to store the generated secret key
 */
void
brandt_ec_skey_create (gcry_mpi_t skey)
{
	gcry_mpi_t   ret;
	gcry_sexp_t  s_keyparam;
	gcry_sexp_t  priv_sexp;
	gcry_sexp_t  priv_key;
	gcry_sexp_t  priv_key2;
	gcry_error_t rc;

	rc = gcry_sexp_build (&s_keyparam, NULL, "(genkey(ecc(curve \"" CURVE "\")"
	                      "(flags)))");
	brandt_assert_gpgerr (rc);

	rc = gcry_pk_genkey (&priv_sexp, s_keyparam);
	brandt_assert_gpgerr (rc);
	gcry_sexp_release (s_keyparam);

	priv_key = gcry_sexp_find_token (priv_sexp, "private-key", 11);
	brandt_assert (NULL != priv_key);
	gcry_sexp_release (priv_sexp);

	priv_key2 = gcry_sexp_find_token (priv_key, "d", 1);
	brandt_assert (NULL != priv_key2);
	gcry_sexp_release (priv_key);

	ret = gcry_sexp_nth_mpi (priv_key2, 1, GCRYMPI_FMT_USG);
	brandt_assert (NULL != ret);
	gcry_sexp_release (priv_key2);

	gcry_mpi_snatch (skey, ret);
}


/**
 * brandt_ec_keypair_create
 *
 * @param[out] pkey where to store the generated public key
 * @param[out] skey where to store the generated secret key
 */
void
brandt_ec_keypair_create (gcry_mpi_point_t pkey, gcry_mpi_t skey)
{
	brandt_assert (NULL != pkey);
	brandt_assert (NULL != skey);

	brandt_ec_skey_create (skey);
	gcry_mpi_ec_mul (pkey, skey, ec_gen, ec_ctx);
}


/**
 * brandt_ec_keypair_create_base
 *
 * @param[out] pkey where to store the generated public key
 * @param[out] skey where to store the generated secret key
 * @param[in] base which base point should be used to calculate the public key
 */
void
brandt_ec_keypair_create_base (gcry_mpi_point_t       pkey,
                               gcry_mpi_t             skey,
                               const gcry_mpi_point_t base)
{
	brandt_assert (NULL != pkey);
	brandt_assert (NULL != skey);
	brandt_assert (NULL != base);

	brandt_ec_skey_create (skey);
	gcry_mpi_ec_mul (pkey, skey, base, ec_ctx);
}


/**
 * brandt_ec_point_cmp compares two curve points
 *
 * @param[in] a the first point
 * @param[in] b the second point
 * @return 0 if @a a and @a b represent the same point on the curve, something
 * else otherwise
 */
int
brandt_ec_point_cmp (const gcry_mpi_point_t a, const gcry_mpi_point_t b)
{
	int        ret = 1;
	gcry_mpi_t ax = gcry_mpi_new (0);
	gcry_mpi_t bx = gcry_mpi_new (0);
	gcry_mpi_t ay = gcry_mpi_new (0);
	gcry_mpi_t by = gcry_mpi_new (0);

	brandt_assert (a && b);
	if (!ax || !bx || !ay || !by)
	{
		weprintf ("could not init point in point_cmp");
		return 1;
	}

	if (!gcry_mpi_ec_get_affine (ax, ay, a, ec_ctx) &&
	    !gcry_mpi_ec_get_affine (bx, by, b, ec_ctx))
	{
		ret = gcry_mpi_cmp (ax, bx) || gcry_mpi_cmp (ay, by);
	}

	gcry_mpi_release (ax);
	gcry_mpi_release (bx);
	gcry_mpi_release (ay);
	gcry_mpi_release (by);
	return ret;
}


/**
 * Clear memory that was used to store a private key.
 *
 * @param skey location of the key
 */
void
brandt_ec_key_clear (struct brandt_ec_skey *skey)
{
	memset (skey, 0, sizeof (struct brandt_ec_skey));
}


/**
 * Generate a random value mod n.
 *
 * @param edc ECC context
 * @return random value mod n.
 */
//gcry_mpi_t
//GNUNET_CRYPTO_ecc_random_mod_n (struct GNUNET_CRYPTO_EccDlogContext *edc)
//{
//  gcry_mpi_t n;
//  unsigned int highbit;
//  gcry_mpi_t r;
//
//  n = gcry_mpi_ec_get_mpi ("n", edc->ctx, 1);
//
//  /* check public key for number of bits, bail out if key is all zeros */
//  highbit = 256; /* Curve25519 */
//  while ( (! gcry_mpi_test_bit (n, highbit)) &&
//          (0 != highbit) )
//    highbit--;
//  GNUNET_assert (0 != highbit);
//  /* generate fact < n (without bias) */
//  GNUNET_assert (NULL != (r = gcry_mpi_new (0)));
//  do {
//    gcry_mpi_randomize (r,
//			highbit + 1,
//			GCRY_STRONG_RANDOM);
//  }
//  while (gcry_mpi_cmp (r, n) >= 0);
//  gcry_mpi_release (n);
//  return r;
//}