mirror of
https://github.com/ClassiCube/ClassiCube.git
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122 lines
3.5 KiB
C
122 lines
3.5 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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/* see bearssl_rsa.h */
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uint32_t
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br_rsa_pkcs1_sig_unpad(const unsigned char *sig, size_t sig_len,
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const unsigned char *hash_oid, size_t hash_len,
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unsigned char *hash_out)
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{
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static const unsigned char pad1[] = {
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0x00, 0x01, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF
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};
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unsigned char pad2[43];
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size_t u, x2, x3, pad_len, zlen;
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if (sig_len < 11) {
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return 0;
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}
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/*
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* Expected format:
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* 00 01 FF ... FF 00 30 x1 30 x2 06 x3 OID [ 05 00 ] 04 x4 HASH
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*
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* with the following rules:
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*
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* -- Total length is that of the modulus and the signature
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* (this was already verified by br_rsa_i31_public()).
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*
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* -- There are at least eight bytes of value 0xFF.
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*
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* -- x4 is equal to the hash length (hash_len).
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*
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* -- x3 is equal to the encoded OID value length (so x3 is the
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* first byte of hash_oid[]).
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*
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* -- If the "05 00" is present, then x2 == x3 + 4; otherwise,
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* x2 == x3 + 2.
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*
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* -- x1 == x2 + x4 + 4.
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*
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* So the total length after the last "FF" is either x3 + x4 + 11
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* (with the "05 00") or x3 + x4 + 9 (without the "05 00").
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*/
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/*
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* Check the "00 01 FF .. FF 00" with at least eight 0xFF bytes.
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* The comparison is valid because we made sure that the signature
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* is at least 11 bytes long.
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*/
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if (br_memcmp(sig, pad1, sizeof pad1) != 0) {
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return 0;
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}
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for (u = sizeof pad1; u < sig_len; u ++) {
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if (sig[u] != 0xFF) {
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break;
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}
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}
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/*
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* Remaining length is sig_len - u bytes (including the 00 just
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* after the last FF). This must be equal to one of the two
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* possible values (depending on whether the "05 00" sequence is
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* present or not).
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*/
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if (hash_oid == NULL) {
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if (sig_len - u != hash_len + 1 || sig[u] != 0x00) {
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return 0;
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}
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} else {
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x3 = hash_oid[0];
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pad_len = x3 + 9;
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br_memset(pad2, 0, pad_len);
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zlen = sig_len - u - hash_len;
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if (zlen == pad_len) {
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x2 = x3 + 2;
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} else if (zlen == pad_len + 2) {
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x2 = x3 + 4;
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pad_len = zlen;
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pad2[pad_len - 4] = 0x05;
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} else {
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return 0;
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}
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pad2[1] = 0x30;
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pad2[2] = x2 + hash_len + 4;
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pad2[3] = 0x30;
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pad2[4] = x2;
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pad2[5] = 0x06;
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br_memcpy(pad2 + 6, hash_oid, x3 + 1);
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pad2[pad_len - 2] = 0x04;
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pad2[pad_len - 1] = hash_len;
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if (br_memcmp(pad2, sig + u, pad_len) != 0) {
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return 0;
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}
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}
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br_memcpy(hash_out, sig + sig_len - hash_len, hash_len);
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return 1;
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}
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