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/* ecc-eddsa.c - Elliptic Curve EdDSA signatures
* Copyright (C) 2013 g10 Code GmbH
*
* This file is part of Libgcrypt.
*
* Libgcrypt is free software; you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as
* published by the Free Software Foundation; either version 2.1 of
* the License, or (at your option) any later version.
*
* Libgcrypt 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 Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this program; if not, see <http://www.gnu.org/licenses/>.
*/
#include <config.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include "g10lib.h"
#include "mpi.h"
#include "cipher.h"
#include "context.h"
#include "ec-context.h"
#include "ecc-common.h"
static void
reverse_buffer (unsigned char *buffer, unsigned int length)
{
unsigned int tmp, i;
for (i=0; i < length/2; i++)
{
tmp = buffer[i];
buffer[i] = buffer[length-1-i];
buffer[length-1-i] = tmp;
}
}
/* Helper to scan a hex string. */
static gcry_mpi_t
scanval (const char *string)
{
gpg_error_t err;
gcry_mpi_t val;
err = gcry_mpi_scan (&val, GCRYMPI_FMT_HEX, string, 0, NULL);
if (err)
log_fatal ("scanning ECC parameter failed: %s\n", gpg_strerror (err));
return val;
}
/* Encode MPI using the EdDSA scheme. MINLEN specifies the required
length of the buffer in bytes. On success 0 is returned an a
malloced buffer with the encoded point is stored at R_BUFFER; the
length of this buffer is stored at R_BUFLEN. */
static gpg_err_code_t
eddsa_encodempi (gcry_mpi_t mpi, unsigned int minlen,
unsigned char **r_buffer, unsigned int *r_buflen)
{
unsigned char *rawmpi;
unsigned int rawmpilen;
rawmpi = _gcry_mpi_get_buffer (mpi, minlen, &rawmpilen, NULL);
if (!rawmpi)
return gpg_err_code_from_syserror ();
*r_buffer = rawmpi;
*r_buflen = rawmpilen;
return 0;
}
/* Encode (X,Y) using the EdDSA scheme. MINLEN is the required length
in bytes for the result. On success 0 is returned and a malloced
buffer with the encoded point is stored at R_BUFFER; the length of
this buffer is stored at R_BUFLEN. */
static gpg_err_code_t
eddsa_encode_x_y (gcry_mpi_t x, gcry_mpi_t y, unsigned int minlen,
unsigned char **r_buffer, unsigned int *r_buflen)
{
unsigned char *rawmpi;
unsigned int rawmpilen;
rawmpi = _gcry_mpi_get_buffer (y, minlen, &rawmpilen, NULL);
if (!rawmpi)
return gpg_err_code_from_syserror ();
if (mpi_test_bit (x, 0) && rawmpilen)
rawmpi[rawmpilen - 1] |= 0x80; /* Set sign bit. */
*r_buffer = rawmpi;
*r_buflen = rawmpilen;
return 0;
}
/* Encode POINT using the EdDSA scheme. X and Y are either scratch
variables supplied by the caller or NULL. CTX is the usual
context. On success 0 is returned and a malloced buffer with the
encoded point is stored at R_BUFFER; the length of this buffer is
stored at R_BUFLEN. */
gpg_err_code_t
_gcry_ecc_eddsa_encodepoint (mpi_point_t point, mpi_ec_t ec,
gcry_mpi_t x_in, gcry_mpi_t y_in,
unsigned char **r_buffer, unsigned int *r_buflen)
{
gpg_err_code_t rc;
gcry_mpi_t x, y;
x = x_in? x_in : mpi_new (0);
y = y_in? y_in : mpi_new (0);
if (_gcry_mpi_ec_get_affine (x, y, point, ec))
{
log_error ("eddsa_encodepoint: Failed to get affine coordinates\n");
rc = GPG_ERR_INTERNAL;
}
else
rc = eddsa_encode_x_y (x, y, ec->nbits/8, r_buffer, r_buflen);
if (!x_in)
mpi_free (x);
if (!y_in)
mpi_free (y);
return rc;
}
/* Make sure that the opaque MPI VALUE is in compact EdDSA format.
This function updates MPI if needed. */
gpg_err_code_t
_gcry_ecc_eddsa_ensure_compact (gcry_mpi_t value, unsigned int nbits)
{
gpg_err_code_t rc;
const unsigned char *buf;
unsigned int rawmpilen;
gcry_mpi_t x, y;
unsigned char *enc;
unsigned int enclen;
if (!mpi_is_opaque (value))
return GPG_ERR_INV_OBJ;
buf = gcry_mpi_get_opaque (value, &rawmpilen);
if (!buf)
return GPG_ERR_INV_OBJ;
rawmpilen = (rawmpilen + 7)/8;
/* Check whether the public key has been given in standard
uncompressed format. In this case extract y and compress. */
if (rawmpilen > 1 && buf[0] == 0x04 && (rawmpilen%2))
{
rc = gcry_mpi_scan (&x, GCRYMPI_FMT_STD,
buf+1, (rawmpilen-1)/2, NULL);
if (rc)
return rc;
rc = gcry_mpi_scan (&y, GCRYMPI_FMT_STD,
buf+1+(rawmpilen-1)/2, (rawmpilen-1)/2, NULL);
if (rc)
{
mpi_free (x);
return rc;
}
rc = eddsa_encode_x_y (x, y, nbits/8, &enc, &enclen);
mpi_free (x);
mpi_free (y);
if (rc)
return rc;
gcry_mpi_set_opaque (value, enc, 8*enclen);
}
return 0;
}
/* Recover X from Y and SIGN (which actually is a parity bit). */
gpg_err_code_t
_gcry_ecc_eddsa_recover_x (gcry_mpi_t x, gcry_mpi_t y, int sign, mpi_ec_t ec)
{
gpg_err_code_t rc = 0;
gcry_mpi_t u, v, v3, t;
static gcry_mpi_t p58, seven;
if (ec->dialect != ECC_DIALECT_ED25519)
return GPG_ERR_NOT_IMPLEMENTED;
if (!p58)
p58 = scanval ("0FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF"
"FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFD");
if (!seven)
seven = mpi_set_ui (NULL, 7);
u = mpi_new (0);
v = mpi_new (0);
v3 = mpi_new (0);
t = mpi_new (0);
/* Compute u and v */
/* u = y^2 */
mpi_mulm (u, y, y, ec->p);
/* v = b*y^2 */
mpi_mulm (v, ec->b, u, ec->p);
/* u = y^2-1 */
mpi_sub_ui (u, u, 1);
/* v = b*y^2+1 */
mpi_add_ui (v, v, 1);
/* Compute sqrt(u/v) */
/* v3 = v^3 */
mpi_powm (v3, v, mpi_const (MPI_C_THREE), ec->p);
/* t = v3 * v3 * u * v = u * v^7 */
mpi_powm (t, v, seven, ec->p);
mpi_mulm (t, t, u, ec->p);
/* t = t^((p-5)/8) = (u * v^7)^((p-5)/8) */
mpi_powm (t, t, p58, ec->p);
/* x = t * u * v^3 = (u * v^3) * (u * v^7)^((p-5)/8) */
mpi_mulm (t, t, u, ec->p);
mpi_mulm (x, t, v3, ec->p);
/* Adjust if needed. */
/* t = v * x^2 */
mpi_mulm (t, x, x, ec->p);
mpi_mulm (t, t, v, ec->p);
/* -t == u ? x = x * sqrt(-1) */
gcry_mpi_neg (t, t);
if (!mpi_cmp (t, u))
{
static gcry_mpi_t m1; /* Fixme: this is not thread-safe. */
if (!m1)
m1 = scanval ("2B8324804FC1DF0B2B4D00993DFBD7A7"
"2F431806AD2FE478C4EE1B274A0EA0B0");
mpi_mulm (x, x, m1, ec->p);
/* t = v * x^2 */
mpi_mulm (t, x, x, ec->p);
mpi_mulm (t, t, v, ec->p);
/* -t == u ? x = x * sqrt(-1) */
gcry_mpi_neg (t, t);
if (!mpi_cmp (t, u))
rc = GPG_ERR_INV_OBJ;
}
/* Choose the desired square root according to parity */
if (mpi_test_bit (x, 0) != !!sign)
gcry_mpi_neg (x, x);
mpi_free (t);
mpi_free (v3);
mpi_free (v);
mpi_free (u);
return rc;
}
/* Decode the EdDSA style encoded PK and set it into RESULT. CTX is
the usual curve context. If R_ENCPK is not NULL, the encoded PK is
stored at that address; this is a new copy to be released by the
caller. In contrast to the supplied PK, this is not an MPI and
thus guarnateed to be properly padded. R_ENCPKLEN received the
length of that encoded key. */
gpg_err_code_t
_gcry_ecc_eddsa_decodepoint (gcry_mpi_t pk, mpi_ec_t ctx, mpi_point_t result,
unsigned char **r_encpk, unsigned int *r_encpklen)
{
gpg_err_code_t rc;
unsigned char *rawmpi;
unsigned int rawmpilen;
int sign;
if (mpi_is_opaque (pk))
{
const unsigned char *buf;
buf = gcry_mpi_get_opaque (pk, &rawmpilen);
if (!buf)
return GPG_ERR_INV_OBJ;
rawmpilen = (rawmpilen + 7)/8;
/* First check whether the public key has been given in standard
uncompressed format. No need to recover x in this case.
Detection is easy: The size of the buffer will be odd and the
first byte be 0x04. */
if (rawmpilen > 1 && buf[0] == 0x04 && (rawmpilen%2))
{
gcry_mpi_t x, y;
rc = gcry_mpi_scan (&x, GCRYMPI_FMT_STD,
buf+1, (rawmpilen-1)/2, NULL);
if (rc)
return rc;
rc = gcry_mpi_scan (&y, GCRYMPI_FMT_STD,
buf+1+(rawmpilen-1)/2, (rawmpilen-1)/2, NULL);
if (rc)
{
mpi_free (x);
return rc;
}
if (r_encpk)
{
rc = eddsa_encode_x_y (x, y, ctx->nbits/8, r_encpk, r_encpklen);
if (rc)
{
mpi_free (x);
mpi_free (y);
return rc;
}
}
mpi_snatch (result->x, x);
mpi_snatch (result->y, y);
mpi_set_ui (result->z, 1);
return 0;
}
/* EdDSA compressed point. */
rawmpi = gcry_malloc (rawmpilen? rawmpilen:1);
if (!rawmpi)
return gpg_err_code_from_syserror ();
memcpy (rawmpi, buf, rawmpilen);
reverse_buffer (rawmpi, rawmpilen);
}
else
{
/* Note: Without using an opaque MPI it is not reliable possible
to find out whether the public key has been given in
uncompressed format. Thus we expect EdDSA format here. */
rawmpi = _gcry_mpi_get_buffer (pk, ctx->nbits/8, &rawmpilen, NULL);
if (!rawmpi)
return gpg_err_code_from_syserror ();
}
if (rawmpilen)
{
sign = !!(rawmpi[0] & 0x80);
rawmpi[0] &= 0x7f;
}
else
sign = 0;
_gcry_mpi_set_buffer (result->y, rawmpi, rawmpilen, 0);
if (r_encpk)
{
/* Revert to little endian. */
if (sign && rawmpilen)
rawmpi[0] |= 0x80;
reverse_buffer (rawmpi, rawmpilen);
*r_encpk = rawmpi;
if (r_encpklen)
*r_encpklen = rawmpilen;
}
else
gcry_free (rawmpi);
rc = _gcry_ecc_eddsa_recover_x (result->x, result->y, sign, ctx);
mpi_set_ui (result->z, 1);
return rc;
}
/* Ed25519 version of the key generation. */
gpg_err_code_t
_gcry_ecc_eddsa_genkey (ECC_secret_key *sk, elliptic_curve_t *E, mpi_ec_t ctx,
gcry_random_level_t random_level)
{
gpg_err_code_t rc;
int b = 256/8; /* The only size we currently support. */
gcry_mpi_t a, x, y;
mpi_point_struct Q;
char *dbuf;
size_t dlen;
gcry_buffer_t hvec[1];
unsigned char *hash_d = NULL;
point_init (&Q);
memset (hvec, 0, sizeof hvec);
a = mpi_snew (0);
x = mpi_new (0);
y = mpi_new (0);
/* Generate a secret. */
hash_d = gcry_malloc_secure (2*b);
if (!hash_d)
{
rc = gpg_error_from_syserror ();
goto leave;
}
dlen = b;
dbuf = gcry_random_bytes_secure (dlen, random_level);
/* Compute the A value. */
hvec[0].data = dbuf;
hvec[0].len = dlen;
rc = _gcry_md_hash_buffers (GCRY_MD_SHA512, 0, hash_d, hvec, 1);
if (rc)
goto leave;
sk->d = _gcry_mpi_set_opaque (NULL, dbuf, dlen*8);
dbuf = NULL;
reverse_buffer (hash_d, 32); /* Only the first half of the hash. */
hash_d[0] = (hash_d[0] & 0x7f) | 0x40;
hash_d[31] &= 0xf8;
_gcry_mpi_set_buffer (a, hash_d, 32, 0);
gcry_free (hash_d); hash_d = NULL;
/* log_printmpi ("ecgen a", a); */
/* Compute Q. */
_gcry_mpi_ec_mul_point (&Q, a, &E->G, ctx);
if (DBG_CIPHER)
log_printpnt ("ecgen pk", &Q, ctx);
/* Copy the stuff to the key structures. */
sk->E.model = E->model;
sk->E.dialect = E->dialect;
sk->E.p = mpi_copy (E->p);
sk->E.a = mpi_copy (E->a);
sk->E.b = mpi_copy (E->b);
point_init (&sk->E.G);
point_set (&sk->E.G, &E->G);
sk->E.n = mpi_copy (E->n);
point_init (&sk->Q);
point_set (&sk->Q, &Q);
leave:
point_free (&Q);
gcry_mpi_release (a);
gcry_mpi_release (x);
gcry_mpi_release (y);
gcry_free (hash_d);
return rc;
}
/* Compute an EdDSA signature. See:
* [ed25519] 23pp. (PDF) Daniel J. Bernstein, Niels Duif, Tanja
* Lange, Peter Schwabe, Bo-Yin Yang. High-speed high-security
* signatures. Journal of Cryptographic Engineering 2 (2012), 77-89.
* Document ID: a1a62a2f76d23f65d622484ddd09caf8.
* URL: http://cr.yp.to/papers.html#ed25519. Date: 2011.09.26.
*
* Despite that this function requires the specification of a hash
* algorithm, we only support what has been specified by the paper.
* This may change in the future. Note that we don't check the used
* curve; the user is responsible to use Ed25519.
*
* Return the signature struct (r,s) from the message hash. The caller
* must have allocated R_R and S.
*/
gpg_err_code_t
_gcry_ecc_eddsa_sign (gcry_mpi_t input, ECC_secret_key *skey,
gcry_mpi_t r_r, gcry_mpi_t s, int hashalgo, gcry_mpi_t pk)
{
int rc;
mpi_ec_t ctx = NULL;
int b;
unsigned int tmp;
unsigned char *digest;
gcry_buffer_t hvec[3];
const void *mbuf;
size_t mlen;
unsigned char *rawmpi = NULL;
unsigned int rawmpilen;
unsigned char *encpk = NULL; /* Encoded public key. */
unsigned int encpklen;
mpi_point_struct I; /* Intermediate value. */
mpi_point_struct Q; /* Public key. */
gcry_mpi_t a, x, y, r;
memset (hvec, 0, sizeof hvec);
if (!mpi_is_opaque (input))
return GPG_ERR_INV_DATA;
if (hashalgo != GCRY_MD_SHA512)
return GPG_ERR_DIGEST_ALGO;
/* Initialize some helpers. */
point_init (&I);
point_init (&Q);
a = mpi_snew (0);
x = mpi_new (0);
y = mpi_new (0);
r = mpi_new (0);
ctx = _gcry_mpi_ec_p_internal_new (skey->E.model, skey->E.dialect, 0,
skey->E.p, skey->E.a, skey->E.b);
b = (ctx->nbits+7)/8;
if (b != 256/8)
return GPG_ERR_INTERNAL; /* We only support 256 bit. */
digest = gcry_calloc_secure (2, b);
if (!digest)
{
rc = gpg_err_code_from_syserror ();
goto leave;
}
/* Hash the secret key. We clear DIGEST so we can use it as input
to left pad the key with zeroes for hashing. */
rawmpi = _gcry_mpi_get_buffer (skey->d, 0, &rawmpilen, NULL);
if (!rawmpi)
{
rc = gpg_err_code_from_syserror ();
goto leave;
}
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;
rc = _gcry_md_hash_buffers (hashalgo, 0, digest, hvec, 2);
gcry_free (rawmpi); rawmpi = NULL;
if (rc)
goto leave;
/* Compute the A value (this modifies DIGEST). */
reverse_buffer (digest, 32); /* Only the first half of the hash. */
digest[0] = (digest[0] & 0x7f) | 0x40;
digest[31] &= 0xf8;
_gcry_mpi_set_buffer (a, digest, 32, 0);
/* Compute the public key if it has not been supplied as optional
parameter. */
if (pk)
{
rc = _gcry_ecc_eddsa_decodepoint (pk, ctx, &Q, &encpk, &encpklen);
if (rc)
goto leave;
if (DBG_CIPHER)
log_printhex ("* e_pk", encpk, encpklen);
if (!_gcry_mpi_ec_curve_point (&Q, ctx))
{
rc = GPG_ERR_BROKEN_PUBKEY;
goto leave;
}
}
else
{
_gcry_mpi_ec_mul_point (&Q, a, &skey->E.G, ctx);
rc = _gcry_ecc_eddsa_encodepoint (&Q, ctx, x, y, &encpk, &encpklen);
if (rc)
goto leave;
if (DBG_CIPHER)
log_printhex (" e_pk", encpk, encpklen);
}
/* Compute R. */
mbuf = gcry_mpi_get_opaque (input, &tmp);
mlen = (tmp +7)/8;
if (DBG_CIPHER)
log_printhex (" m", mbuf, mlen);
hvec[0].data = digest;
hvec[0].off = 32;
hvec[0].len = 32;
hvec[1].data = (char*)mbuf;
hvec[1].len = mlen;
rc = _gcry_md_hash_buffers (hashalgo, 0, digest, hvec, 2);
if (rc)
goto leave;
reverse_buffer (digest, 64);
if (DBG_CIPHER)
log_printhex (" r", digest, 64);
_gcry_mpi_set_buffer (r, digest, 64, 0);
_gcry_mpi_ec_mul_point (&I, r, &skey->E.G, ctx);
if (DBG_CIPHER)
log_printpnt (" r", &I, ctx);
/* Convert R into affine coordinates and apply encoding. */
rc = _gcry_ecc_eddsa_encodepoint (&I, ctx, x, y, &rawmpi, &rawmpilen);
if (rc)
goto leave;
if (DBG_CIPHER)
log_printhex (" e_r", rawmpi, rawmpilen);
/* S = r + a * H(encodepoint(R) + encodepoint(pk) + m) mod n */
hvec[0].data = rawmpi; /* (this is R) */
hvec[0].off = 0;
hvec[0].len = rawmpilen;
hvec[1].data = encpk;
hvec[1].off = 0;
hvec[1].len = encpklen;
hvec[2].data = (char*)mbuf;
hvec[2].off = 0;
hvec[2].len = mlen;
rc = _gcry_md_hash_buffers (hashalgo, 0, digest, hvec, 3);
if (rc)
goto leave;
/* No more need for RAWMPI thus we now transfer it to R_R. */
gcry_mpi_set_opaque (r_r, rawmpi, rawmpilen*8);
rawmpi = NULL;
reverse_buffer (digest, 64);
if (DBG_CIPHER)
log_printhex (" H(R+)", digest, 64);
_gcry_mpi_set_buffer (s, digest, 64, 0);
mpi_mulm (s, s, a, skey->E.n);
mpi_addm (s, s, r, skey->E.n);
rc = eddsa_encodempi (s, b, &rawmpi, &rawmpilen);
if (rc)
goto leave;
if (DBG_CIPHER)
log_printhex (" e_s", rawmpi, rawmpilen);
gcry_mpi_set_opaque (s, rawmpi, rawmpilen*8);
rawmpi = NULL;
rc = 0;
leave:
gcry_mpi_release (a);
gcry_mpi_release (x);
gcry_mpi_release (y);
gcry_mpi_release (r);
gcry_free (digest);
_gcry_mpi_ec_free (ctx);
point_free (&I);
point_free (&Q);
gcry_free (encpk);
gcry_free (rawmpi);
return rc;
}
/* Verify an EdDSA signature. See sign_eddsa for the reference.
* Check if R_IN and S_IN verifies INPUT. PKEY has the curve
* parameters and PK is the EdDSA style encoded public key.
*/
gpg_err_code_t
_gcry_ecc_eddsa_verify (gcry_mpi_t input, ECC_public_key *pkey,
gcry_mpi_t r_in, gcry_mpi_t s_in, int hashalgo,
gcry_mpi_t pk)
{
int rc;
mpi_ec_t ctx = NULL;
int b;
unsigned int tmp;
mpi_point_struct Q; /* Public key. */
unsigned char *encpk = NULL; /* Encoded public key. */
unsigned int encpklen;
const void *mbuf, *rbuf;
unsigned char *tbuf = NULL;
size_t mlen, rlen;
unsigned int tlen;
unsigned char digest[64];
gcry_buffer_t hvec[3];
gcry_mpi_t h, s;
mpi_point_struct Ia, Ib;
if (!mpi_is_opaque (input) || !mpi_is_opaque (r_in) || !mpi_is_opaque (s_in))
return GPG_ERR_INV_DATA;
if (hashalgo != GCRY_MD_SHA512)
return GPG_ERR_DIGEST_ALGO;
point_init (&Q);
point_init (&Ia);
point_init (&Ib);
h = mpi_new (0);
s = mpi_new (0);
ctx = _gcry_mpi_ec_p_internal_new (pkey->E.model, pkey->E.dialect, 0,
pkey->E.p, pkey->E.a, pkey->E.b);
b = ctx->nbits/8;
if (b != 256/8)
return GPG_ERR_INTERNAL; /* We only support 256 bit. */
/* Decode and check the public key. */
rc = _gcry_ecc_eddsa_decodepoint (pk, ctx, &Q, &encpk, &encpklen);
if (rc)
goto leave;
if (!_gcry_mpi_ec_curve_point (&Q, ctx))
{
rc = GPG_ERR_BROKEN_PUBKEY;
goto leave;
}
if (DBG_CIPHER)
log_printhex (" e_pk", encpk, encpklen);
if (encpklen != b)
{
rc = GPG_ERR_INV_LENGTH;
goto leave;
}
/* Convert the other input parameters. */
mbuf = gcry_mpi_get_opaque (input, &tmp);
mlen = (tmp +7)/8;
if (DBG_CIPHER)
log_printhex (" m", mbuf, mlen);
rbuf = gcry_mpi_get_opaque (r_in, &tmp);
rlen = (tmp +7)/8;
if (DBG_CIPHER)
log_printhex (" r", rbuf, rlen);
if (rlen != b)
{
rc = GPG_ERR_INV_LENGTH;
goto leave;
}
/* h = H(encodepoint(R) + encodepoint(pk) + m) */
hvec[0].data = (char*)rbuf;
hvec[0].off = 0;
hvec[0].len = rlen;
hvec[1].data = encpk;
hvec[1].off = 0;
hvec[1].len = encpklen;
hvec[2].data = (char*)mbuf;
hvec[2].off = 0;
hvec[2].len = mlen;
rc = _gcry_md_hash_buffers (hashalgo, 0, digest, hvec, 3);
if (rc)
goto leave;
reverse_buffer (digest, 64);
if (DBG_CIPHER)
log_printhex (" H(R+)", digest, 64);
_gcry_mpi_set_buffer (h, digest, 64, 0);
/* According to the paper the best way for verification is:
encodepoint(sG - h·Q) = encodepoint(r)
because we don't need to decode R. */
{
void *sbuf;
unsigned int slen;
sbuf = _gcry_mpi_get_opaque_copy (s_in, &tmp);
slen = (tmp +7)/8;
reverse_buffer (sbuf, slen);
if (DBG_CIPHER)
log_printhex (" s", sbuf, slen);
_gcry_mpi_set_buffer (s, sbuf, slen, 0);
gcry_free (sbuf);
if (slen != b)
{
rc = GPG_ERR_INV_LENGTH;
goto leave;
}
}
_gcry_mpi_ec_mul_point (&Ia, s, &pkey->E.G, ctx);
_gcry_mpi_ec_mul_point (&Ib, h, &Q, ctx);
_gcry_mpi_neg (Ib.x, Ib.x);
_gcry_mpi_ec_add_points (&Ia, &Ia, &Ib, ctx);
rc = _gcry_ecc_eddsa_encodepoint (&Ia, ctx, s, h, &tbuf, &tlen);
if (rc)
goto leave;
if (tlen != rlen || memcmp (tbuf, rbuf, tlen))
{
rc = GPG_ERR_BAD_SIGNATURE;
goto leave;
}
rc = 0;
leave:
gcry_free (encpk);
gcry_free (tbuf);
_gcry_mpi_ec_free (ctx);
gcry_mpi_release (s);
gcry_mpi_release (h);
point_free (&Ia);
point_free (&Ib);
point_free (&Q);
return rc;
}

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