114 lines
2.8 KiB
C
114 lines
2.8 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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/*
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* As a strict minimum, we need four buffers that can hold a
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* modular integer.
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*/
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#define TLEN (4 * (2 + ((BR_MAX_RSA_SIZE + 14) / 15)))
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/* see bearssl_rsa.h */
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uint32_t
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br_rsa_i15_public(unsigned char *x, size_t xlen,
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const br_rsa_public_key *pk)
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{
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const unsigned char *n;
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size_t nlen;
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uint16_t tmp[1 + TLEN];
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uint16_t *m, *a, *t;
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size_t fwlen;
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long z;
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uint16_t m0i;
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uint32_t r;
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/*
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* Get the actual length of the modulus, and see if it fits within
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* our stack buffer. We also check that the length of x[] is valid.
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*/
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n = pk->n;
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nlen = pk->nlen;
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while (nlen > 0 && *n == 0) {
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n ++;
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nlen --;
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}
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if (nlen == 0 || nlen > (BR_MAX_RSA_SIZE >> 3) || xlen != nlen) {
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return 0;
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}
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z = (long)nlen << 3;
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fwlen = 1;
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while (z > 0) {
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z -= 15;
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fwlen ++;
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}
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/*
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* Round up length to an even number.
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*/
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fwlen += (fwlen & 1);
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/*
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* The modulus gets decoded into m[].
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* The value to exponentiate goes into a[].
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* The temporaries for modular exponentiations are in t[].
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*
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* We want the first value word of each integer to be aligned
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* on a 32-bit boundary.
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*/
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m = tmp;
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if (((uintptr_t)m & 2) == 0) {
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m ++;
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}
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a = m + fwlen;
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t = m + 2 * fwlen;
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/*
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* Decode the modulus.
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*/
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br_i15_decode(m, n, nlen);
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m0i = br_i15_ninv15(m[1]);
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/*
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* Note: if m[] is even, then m0i == 0. Otherwise, m0i must be
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* an odd integer.
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*/
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r = m0i & 1;
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/*
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* Decode x[] into a[]; we also check that its value is proper.
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*/
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r &= br_i15_decode_mod(a, x, xlen, m);
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/*
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* Compute the modular exponentiation.
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*/
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br_i15_modpow_opt(a, pk->e, pk->elen, m, m0i, t, TLEN - 2 * fwlen);
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/*
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* Encode the result.
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*/
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br_i15_encode(x, xlen, a);
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return r;
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}
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