77 lines
2.3 KiB
C
77 lines
2.3 KiB
C
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/*
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prf.c -- Pseudo-Random Function for key material generation
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Copyright (C) 2011 Guus Sliepen <guus@tinc-vpn.org>
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License along
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with this program; if not, write to the Free Software Foundation, Inc.,
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51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
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*/
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#include "system.h"
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#include "digest.h"
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#include "prf.h"
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/* Generate key material from a master secret and a seed, based on RFC 2246.
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We use SHA512 and Whirlpool instead of MD5 and SHA1.
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*/
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static bool prf_xor(int nid, char *secret, size_t secretlen, char *seed, size_t seedlen, char *out, ssize_t outlen) {
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digest_t digest;
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if(!digest_open_by_nid(&digest, nid, 0))
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return false;
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if(!digest_set_key(&digest, secret, secretlen))
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return false;
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size_t len = digest_length(&digest);
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/* Data is what the "inner" HMAC function processes.
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It consists of the previous HMAC result plus the seed.
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*/
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char data[len + seedlen];
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memset(data, 0, len);
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memcpy(data + len, seed, seedlen);
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char hash[len];
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while(outlen > 0) {
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/* Inner HMAC */
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digest_create(&digest, data, len + seedlen, data);
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/* Outer HMAC */
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digest_create(&digest, data, len + seedlen, hash);
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/* XOR the results of the outer HMAC into the out buffer */
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for(int i = 0; i < len && i < outlen; i++)
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*out++ ^= hash[i];
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outlen -= len;
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}
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digest_close(&digest);
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return true;
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}
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bool prf(char *secret, size_t secretlen, char *seed, size_t seedlen, char *out, size_t outlen) {
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/* Split secret in half, generate outlen bits with two different hash algorithms,
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and XOR the results. */
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memset(out, 0, outlen);
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return prf_xor(NID_sha512, secret, secretlen / 2, seed, seedlen, out, outlen)
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&& prf_xor(NID_whirlpool, secret, secretlen / 2, seed, seedlen, out, outlen);
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}
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