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/*
* Copyright (c) 2018 Thomas Pornin <[email protected]>
*
* Permission is hereby granted, free of charge, to any person obtaining
* a copy of this software and associated documentation files (the
* "Software"), to deal in the Software without restriction, including
* without limitation the rights to use, copy, modify, merge, publish,
* distribute, sublicense, and/or sell copies of the Software, and to
* permit persons to whom the Software is furnished to do so, subject to
* the following conditions:
*
* The above copyright notice and this permission notice shall be
* included in all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
* BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
* ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE.
*/
#include "inner.h"
/* see bearssl_ec.h */
size_t
br_ec_keygen(const br_prng_class **rng_ctx,
const br_ec_impl *impl, br_ec_private_key *sk,
void *kbuf, int curve)
{
const unsigned char *order;
unsigned char *buf;
size_t len;
unsigned mask;
if (curve < 0 || curve >= 32
|| ((impl->supported_curves >> curve) & 1) == 0)
{
return 0;
}
order = impl->order(curve, &len);
while (len > 0 && *order == 0) {
order ++;
len --;
}
if (kbuf == NULL || len == 0) {
return len;
}
mask = order[0];
mask |= (mask >> 1);
mask |= (mask >> 2);
mask |= (mask >> 4);
/*
* We generate sequences of random bits of the right size, until
* the value is strictly lower than the curve order (we also
* check for all-zero values, which are invalid).
*/
buf = kbuf;
for (;;) {
size_t u;
unsigned cc, zz;
(*rng_ctx)->generate(rng_ctx, buf, len);
buf[0] &= mask;
cc = 0;
u = len;
zz = 0;
while (u -- > 0) {
cc = ((unsigned)(buf[u] - order[u] - cc) >> 8) & 1;
zz |= buf[u];
}
if (cc != 0 && zz != 0) {
break;
}
}
if (sk != NULL) {
sk->curve = curve;
sk->x = buf;
sk->xlen = len;
}
return len;
}
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