146 lines
4.1 KiB
C
146 lines
4.1 KiB
C
/*
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* Copyright (c) 2017 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 "inner.h"
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#define U (1 + ((BR_MAX_RSA_FACTOR + 14) / 15))
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/* see bearssl_rsa.h */
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uint32_t
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br_rsa_i15_private(unsigned char *x, const br_rsa_private_key *sk)
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{
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const unsigned char *p, *q;
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size_t plen, qlen;
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uint16_t tmp[6 * U];
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uint16_t *mp, *mq, *s1, *s2, *t1, *t2, *t3;
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uint16_t p0i, q0i;
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size_t xlen;
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/*
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* All our temporary buffers are from the tmp[] array.
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*
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* The mp, mq, s1, s2, t1 and t2 buffers are large enough to
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* contain a RSA factor. The t3 buffer can contain a complete
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* RSA modulus. t3 shares its storage space with s2, s1 and t1,
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* in that order (this is important, see below).
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*/
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mq = tmp;
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mp = tmp + U;
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t2 = tmp + 2 * U;
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s2 = tmp + 3 * U;
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s1 = tmp + 4 * U;
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t1 = tmp + 5 * U;
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t3 = s2;
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/*
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* Compute the actual lengths (in bytes) of p and q, and check
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* that they fit within our stack buffers.
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*/
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p = sk->p;
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plen = sk->plen;
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while (plen > 0 && *p == 0) {
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p ++;
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plen --;
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}
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q = sk->q;
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qlen = sk->qlen;
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while (qlen > 0 && *q == 0) {
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q ++;
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qlen --;
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}
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if (plen > (BR_MAX_RSA_FACTOR >> 3)
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|| qlen > (BR_MAX_RSA_FACTOR >> 3))
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{
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return 0;
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}
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/*
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* Decode p and q.
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*/
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br_i15_decode(mp, p, plen);
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br_i15_decode(mq, q, qlen);
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/*
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* Compute signature length (in bytes).
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*/
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xlen = (sk->n_bitlen + 7) >> 3;
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/*
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* Compute s1 = x^dp mod p.
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*/
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p0i = br_i15_ninv15(mp[1]);
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br_i15_decode_reduce(s1, x, xlen, mp);
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br_i15_modpow(s1, sk->dp, sk->dplen, mp, p0i, t1, t2);
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/*
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* Compute s2 = x^dq mod q.
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*/
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q0i = br_i15_ninv15(mq[1]);
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br_i15_decode_reduce(s2, x, xlen, mq);
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br_i15_modpow(s2, sk->dq, sk->dqlen, mq, q0i, t1, t2);
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/*
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* Compute:
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* h = (s1 - s2)*(1/q) mod p
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* s1 is an integer modulo p, but s2 is modulo q. PKCS#1 is
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* unclear about whether p may be lower than q (some existing,
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* widely deployed implementations of RSA don't tolerate p < q),
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* but we want to support that occurrence, so we need to use the
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* reduction function.
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*
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* Since we use br_i15_decode_reduce() for iq (purportedly, the
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* inverse of q modulo p), we also tolerate improperly large
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* values for this parameter.
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*/
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br_i15_reduce(t2, s2, mp);
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br_i15_add(s1, mp, br_i15_sub(s1, t2, 1));
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br_i15_to_monty(s1, mp);
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br_i15_decode_reduce(t1, sk->iq, sk->iqlen, mp);
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br_i15_montymul(t2, s1, t1, mp, p0i);
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/*
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* h is now in t2. We compute the final result:
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* s = s2 + q*h
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* All these operations are non-modular.
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*
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* We need mq, s2 and t2. We use the t3 buffer as destination.
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* The buffers mp, s1 and t1 are no longer needed. Moreover,
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* the first step is to copy s2 into the destination buffer t3.
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* We thus arranged for t3 to actually share space with s2, and
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* to be followed by the space formerly used by s1 and t1.
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*/
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br_i15_mulacc(t3, mq, t2);
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/*
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* Encode the result. Since we already checked the value of xlen,
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* we can just use it right away.
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*/
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br_i15_encode(x, xlen, t3);
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/*
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* The only error conditions remaining at that point are invalid
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* values for p and q (even integers).
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*/
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return p0i & q0i & 1;
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}
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