/* Helper to extract a point from key parameters. If no parameter
with NAME is found, the functions tries to find a non-encoded point
by appending ".x", ".y" and ".z" to NAME. ".z" is in this case
optional and defaults to 1. EC is the context which at this point
may not be fully initialized. */
static gpg_err_code_t
point_from_keyparam (gcry_mpi_point_t *r_a,
gcry_sexp_t keyparam, const char *name, mpi_ec_t ec)
{
gcry_err_code_t rc;
gcry_sexp_t l1;
gcry_mpi_point_t point;
l1 = sexp_find_token (keyparam, name, 0);
if (l1)
{
gcry_mpi_t a;
a = sexp_nth_mpi (l1, 1, GCRYMPI_FMT_OPAQUE);
sexp_release (l1);
if (!a)
return GPG_ERR_INV_OBJ;
point = mpi_point_new (0);
if (ec && ec->dialect == ECC_DIALECT_ED25519)
rc = _gcry_ecc_eddsa_decodepoint (a, ec, point, NULL, NULL);
else
rc = _gcry_ecc_os2ec (point, a);
mpi_free (a);
if (rc)
{
mpi_point_release (point);
return rc;
}
}
else
{
char *tmpname;
gcry_mpi_t x = NULL;
gcry_mpi_t y = NULL;
gcry_mpi_t z = NULL;
tmpname = xtrymalloc (strlen (name) + 2 + 1);
if (!tmpname)
return gpg_err_code_from_syserror ();
strcpy (stpcpy (tmpname, name), ".x");
rc = mpi_from_keyparam (&x, keyparam, tmpname);
if (rc)
{
xfree (tmpname);
return rc;
}
strcpy (stpcpy (tmpname, name), ".y");
rc = mpi_from_keyparam (&y, keyparam, tmpname);
if (rc)
{
mpi_free (x);
xfree (tmpname);
return rc;
}
strcpy (stpcpy (tmpname, name), ".z");
rc = mpi_from_keyparam (&z, keyparam, tmpname);
if (rc)
{
mpi_free (y);
mpi_free (x);
xfree (tmpname);
return rc;
}
if (!z)
z = mpi_set_ui (NULL, 1);
if (x && y)
point = mpi_point_snatch_set (NULL, x, y, z);
else
{
mpi_free (x);
mpi_free (y);
mpi_free (z);
point = NULL;
}
xfree (tmpname);
}
if (point)
*r_a = point;
return 0;
}
/* 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 = mpi_get_opaque (input, &tmp);
mlen = (tmp +7)/8;
if (DBG_CIPHER)
log_printhex (" m", mbuf, mlen);
rbuf = 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);
xfree (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, 0, &tbuf, &tlen);
if (rc)
goto leave;
if (tlen != rlen || memcmp (tbuf, rbuf, tlen))
{
rc = GPG_ERR_BAD_SIGNATURE;
goto leave;
}
rc = 0;
leave:
xfree (encpk);
xfree (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;
}
/* Store the MPI NEWVALUE into the context EC under NAME. */
gpg_err_code_t
_gcry_ecc_set_mpi (const char *name, gcry_mpi_t newvalue, mpi_ec_t ec)
{
gpg_err_code_t rc = 0;
if (!*name)
;
else if (!strcmp (name, "p"))
{
mpi_free (ec->p);
ec->p = mpi_copy (newvalue);
_gcry_mpi_ec_get_reset (ec);
}
else if (!strcmp (name, "a"))
{
mpi_free (ec->a);
ec->a = mpi_copy (newvalue);
_gcry_mpi_ec_get_reset (ec);
}
else if (!strcmp (name, "b"))
{
mpi_free (ec->b);
ec->b = mpi_copy (newvalue);
}
else if (!strcmp (name, "n"))
{
mpi_free (ec->n);
ec->n = mpi_copy (newvalue);
}
else if (*name == 'q' && (!name[1] || name[1] == '@'))
{
if (newvalue)
{
if (!ec->Q)
ec->Q = mpi_point_new (0);
if (ec->dialect == ECC_DIALECT_ED25519)
rc = _gcry_ecc_eddsa_decodepoint (newvalue, ec, ec->Q, NULL, NULL);
else
rc = _gcry_ecc_os2ec (ec->Q, newvalue);
}
if (rc || !newvalue)
{
_gcry_mpi_point_release (ec->Q);
ec->Q = NULL;
}
/* Note: We assume that Q matches d and thus do not reset d. */
}
else if (!strcmp (name, "d"))
{
mpi_free (ec->d);
ec->d = mpi_copy (newvalue);
if (ec->d)
{
/* We need to reset the public key because it may not
anymore match. */
_gcry_mpi_point_release (ec->Q);
ec->Q = NULL;
}
}
else
rc = GPG_ERR_UNKNOWN_NAME;
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;
/* 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. */
rc = _gcry_ecc_eddsa_compute_h_d (&digest, skey->d, ctx);
if (rc)
goto leave;
_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, 0, &encpk, &encpklen);
if (rc)
goto leave;
if (DBG_CIPHER)
log_printhex (" e_pk", encpk, encpklen);
}
/* Compute R. */
mbuf = 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, 0, &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. */
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);
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);
xfree (digest);
_gcry_mpi_ec_free (ctx);
point_free (&I);
point_free (&Q);
xfree (encpk);
xfree (rawmpi);
return rc;
}
