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/*
* Off-the-Record Messaging Toolkit
* Copyright (C) 2004-2012 Ian Goldberg, Chris Alexander, Nikita Borisov
* <otr@cypherpunks.ca>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of version 2 of the GNU General Public License as
* published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
/* system headers */
#include <stdlib.h>
#include <string.h>
/* toolkit headers */
#include "aes.h"
/* Encrypt or decrypt data in AES-CTR mode. (The operations are the
* same.) We roll our own here just to double-check that the calls
* libotr makes to libgcrypt are doing the right thing. */
void aes_ctr_crypt(unsigned char *out, const unsigned char *in, size_t len,
unsigned char key[16], unsigned char ctrtop[8])
{
unsigned char ctr[16], encctr[16];
aes_context aesc;
aes_set_key(&aesc, key, 128);
memmove(ctr, ctrtop, 8);
memset(ctr+8, 0, 8);
while(len > 0) {
/* How much to do at a time? */
size_t i;
size_t amt = len;
if (amt > 16) amt = 16;
aes_encrypt(&aesc, ctr, encctr);
for(i=0;i<amt;++i) {
out[i] = in[i] ^ encctr[i];
}
/* Increment the counter */
for (i=16;i>0;--i) {
if (++ctr[i-1] != 0) break;
}
out += amt;
in += amt;
len -= amt;
}
}
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