2 * Copyright (c) 2016 Thomas Pornin <pornin@bolet.org>
4 * Permission is hereby granted, free of charge, to any person obtaining
5 * a copy of this software and associated documentation files (the
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7 * without limitation the rights to use, copy, modify, merge, publish,
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9 * permit persons to whom the Software is furnished to do so, subject to
10 * the following conditions:
12 * The above copyright notice and this permission notice shall be
13 * included in all copies or substantial portions of the Software.
15 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
16 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
17 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
18 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
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21 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
27 #if BR_INT128 || BR_UMUL128
30 * As a strict minimum, we need four buffers that can hold a
31 * modular integer. But TLEN is expressed in 64-bit words.
33 #define TLEN (2 * (2 + ((BR_MAX_RSA_SIZE + 30) / 31)))
35 /* see bearssl_rsa.h */
37 br_rsa_i62_public(unsigned char *x, size_t xlen,
38 const br_rsa_public_key *pk)
40 const unsigned char *n;
49 * Get the actual length of the modulus, and see if it fits within
50 * our stack buffer. We also check that the length of x[] is valid.
54 while (nlen > 0 && *n == 0) {
58 if (nlen == 0 || nlen > (BR_MAX_RSA_SIZE >> 3) || xlen != nlen) {
68 * Convert fwlen to a count in 62-bit words.
70 fwlen = (fwlen + 1) >> 1;
73 * The modulus gets decoded into m[].
74 * The value to exponentiate goes into a[].
77 a = (uint32_t *)(tmp + fwlen);
82 br_i31_decode(m, n, nlen);
83 m0i = br_i31_ninv31(m[1]);
86 * Note: if m[] is even, then m0i == 0. Otherwise, m0i must be
92 * Decode x[] into a[]; we also check that its value is proper.
94 r &= br_i31_decode_mod(a, x, xlen, m);
97 * Compute the modular exponentiation.
99 br_i62_modpow_opt(a, pk->e, pk->elen, m, m0i,
100 tmp + 2 * fwlen, TLEN - 2 * fwlen);
105 br_i31_encode(x, xlen, a);
109 /* see bearssl_rsa.h */
111 br_rsa_i62_public_get(void)
113 return &br_rsa_i62_public;
118 /* see bearssl_rsa.h */
120 br_rsa_i62_public_get(void)