/* Turn VALUE into an octet string and store it in an allocated buffer
at R_FRAME. If the resulting octet string is shorter than NBYTES
the result will be left padded with zeroes. If VALUE does not fit
into NBYTES an error code is returned. */
static gpg_err_code_t
int2octets (unsigned char **r_frame, gcry_mpi_t value, size_t nbytes)
{
gpg_err_code_t rc;
size_t nframe, noff, n;
unsigned char *frame;
rc = _gcry_mpi_print (GCRYMPI_FMT_USG, NULL, 0, &nframe, value);
if (rc)
return rc;
if (nframe > nbytes)
return GPG_ERR_TOO_LARGE; /* Value too long to fit into NBYTES. */
noff = (nframe < nbytes)? nbytes - nframe : 0;
n = nframe + noff;
frame = mpi_is_secure (value)? xtrymalloc_secure (n) : xtrymalloc (n);
if (!frame)
return gpg_err_code_from_syserror ();
if (noff)
memset (frame, 0, noff);
nframe += noff;
rc = _gcry_mpi_print (GCRYMPI_FMT_USG, frame+noff, nframe-noff, NULL, value);
if (rc)
{
xfree (frame);
return rc;
}
*r_frame = frame;
return 0;
}
gcry_error_t
gcry_mpi_print (enum gcry_mpi_format format,
unsigned char *buffer, size_t buflen,
size_t *nwritten,
const gcry_mpi_t a)
{
return gpg_error (_gcry_mpi_print (format, buffer, buflen, nwritten, a));
}
gcry_mpi_t
_gcry_ecc_ec2os (gcry_mpi_t x, gcry_mpi_t y, gcry_mpi_t p)
{
gpg_err_code_t rc;
int pbytes = (mpi_get_nbits (p)+7)/8;
size_t n;
unsigned char *buf, *ptr;
gcry_mpi_t result;
buf = xmalloc ( 1 + 2*pbytes );
*buf = 04; /* Uncompressed point. */
ptr = buf+1;
rc = _gcry_mpi_print (GCRYMPI_FMT_USG, ptr, pbytes, &n, x);
if (rc)
log_fatal ("mpi_print failed: %s\n", gpg_strerror (rc));
if (n < pbytes)
{
memmove (ptr+(pbytes-n), ptr, n);
memset (ptr, 0, (pbytes-n));
}
ptr += pbytes;
rc = _gcry_mpi_print (GCRYMPI_FMT_USG, ptr, pbytes, &n, y);
if (rc)
log_fatal ("mpi_print failed: %s\n", gpg_strerror (rc));
if (n < pbytes)
{
memmove (ptr+(pbytes-n), ptr, n);
memset (ptr, 0, (pbytes-n));
}
rc = _gcry_mpi_scan (&result, GCRYMPI_FMT_USG, buf, 1+2*pbytes, NULL);
if (rc)
log_fatal ("mpi_scan failed: %s\n", gpg_strerror (rc));
xfree (buf);
return result;
}
/* RESULT must have been initialized and is set on success to the
point given by VALUE. */
gcry_err_code_t
_gcry_ecc_os2ec (mpi_point_t result, gcry_mpi_t value)
{
gcry_err_code_t rc;
size_t n;
const unsigned char *buf;
unsigned char *buf_memory;
gcry_mpi_t x, y;
if (mpi_is_opaque (value))
{
unsigned int nbits;
buf = mpi_get_opaque (value, &nbits);
if (!buf)
return GPG_ERR_INV_OBJ;
n = (nbits + 7)/8;
buf_memory = NULL;
}
else
{
n = (mpi_get_nbits (value)+7)/8;
buf_memory = xmalloc (n);
rc = _gcry_mpi_print (GCRYMPI_FMT_USG, buf_memory, n, &n, value);
if (rc)
{
xfree (buf_memory);
return rc;
}
buf = buf_memory;
}
if (n < 1)
{
xfree (buf_memory);
return GPG_ERR_INV_OBJ;
}
if (*buf != 4)
{
xfree (buf_memory);
return GPG_ERR_NOT_IMPLEMENTED; /* No support for point compression. */
}
if ( ((n-1)%2) )
{
xfree (buf_memory);
return GPG_ERR_INV_OBJ;
}
n = (n-1)/2;
rc = _gcry_mpi_scan (&x, GCRYMPI_FMT_USG, buf+1, n, NULL);
if (rc)
{
xfree (buf_memory);
return rc;
}
rc = _gcry_mpi_scan (&y, GCRYMPI_FMT_USG, buf+1+n, n, NULL);
xfree (buf_memory);
if (rc)
{
mpi_free (x);
return rc;
}
mpi_set (result->x, x);
mpi_set (result->y, y);
mpi_set_ui (result->z, 1);
mpi_free (x);
mpi_free (y);
return 0;
}