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