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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 <stdio.h>
#include <stdlib.h>
/* libotr headers */
#include "proto.h"
/* toolkit headers */
#include "readotr.h"
#include "parse.h"
#include "sesskeys.h"
#include "sha1hmac.h"
#include "ctrmode.h"
static void usage(const char *progname)
{
fprintf(stderr, "Usage: %s aeskey [new_message]\n"
"Read an OTR Data Message from stdin. Use the given AES key to\n"
"verify its MAC and decrypt the message to stdout. If new_message\n"
"is given, output a new OTR Data Message with the same fields as the\n"
"original, but with the message replaced by new_message\n", progname);
exit(1);
}
int main(int argc, char **argv)
{
unsigned char *aeskey;
unsigned char mackey[20];
unsigned char macval[20];
size_t aeskeylen;
unsigned char *plaintext, *ciphertext;
char *otrmsg = NULL;
DataMsg datamsg;
if (argc != 2 && argc != 3) {
usage(argv[0]);
}
argv_to_buf(&aeskey, &aeskeylen, argv[1]);
if (!aeskey) {
usage(argv[0]);
}
if (aeskeylen != 16) {
fprintf(stderr, "The AES key must be 32 hex chars long.\n");
usage(argv[0]);
}
otrmsg = readotr(stdin);
if (otrmsg == NULL) {
fprintf(stderr, "No OTR Data Message found on stdin.\n");
exit(1);
}
if (otrl_proto_message_type(otrmsg) != OTRL_MSGTYPE_DATA) {
fprintf(stderr, "OTR Non-Data Message found on stdin.\n");
exit(1);
}
datamsg = parse_datamsg(otrmsg);
free(otrmsg);
if (datamsg == NULL) {
fprintf(stderr, "Invalid OTR Data Message found on stdin.\n");
exit(1);
}
/* Create the MAC key */
sesskeys_make_mac(mackey, aeskey);
/* Check the MAC */
sha1hmac(macval, mackey, datamsg->macstart,
datamsg->macend - datamsg->macstart);
if (memcmp(macval, datamsg->mac, 20)) {
fprintf(stderr, "MAC does not verify: wrong AES key?\n");
} else {
/* Decrypt the message */
plaintext = malloc(datamsg->encmsglen+1);
if (!plaintext) {
fprintf(stderr, "Out of memory!\n");
exit(1);
}
aes_ctr_crypt(plaintext, datamsg->encmsg, datamsg->encmsglen,
aeskey, datamsg->ctr);
plaintext[datamsg->encmsglen] = '\0';
printf("Plaintext: ``%s''\n", plaintext);
free(plaintext);
}
/* Do we want to forge a message? */
if (argv[2] != NULL) {
char *newdatamsg;
size_t newlen = strlen(argv[2]);
ciphertext = malloc(newlen);
if (!ciphertext && newlen > 0) {
fprintf(stderr, "Out of memory!\n");
exit(1);
}
aes_ctr_crypt(ciphertext, (const unsigned char *)argv[2], newlen,
aeskey, datamsg->ctr);
free(datamsg->encmsg);
datamsg->encmsg = ciphertext;
datamsg->encmsglen = newlen;
newdatamsg = remac_datamsg(datamsg, mackey);
printf("%s\n", newdatamsg);
free(newdatamsg);
}
free_datamsg(datamsg);
free(aeskey);
fflush(stdout);
return 0;
}