1 files changed, 126 insertions, 0 deletions
diff --git a/comm/third_party/libotr/toolkit/otr_modify.c b/comm/third_party/libotr/toolkit/otr_modify.c
new file mode 100644
index 0000000000..8257b511e1
--- /dev/null
+++ b/comm/third_party/libotr/toolkit/otr_modify.c
@@ -0,0 +1,126 @@
+/*
+ *  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 "sha1hmac.h"
+
+static void usage(const char *progname)
+{
+    fprintf(stderr, "Usage: %s mackey old_text new_text offset\n"
+"Read an OTR Data Message from stdin.  Even if we can't read the\n"
+"data because we don't know either the AES key or the DH privkey,\n"
+"but we can make a good guess that the substring \"old_text\"\n"
+"appears at the given offset in the message, replace the old_text\n"
+"with the new_text (which must be of the same length), recalculate\n"
+"the MAC with the given mackey, and output the resulting Data message.\n",
+    progname);
+    exit(1);
+}
+
+int main(int argc, char **argv)
+{
+    unsigned char *mackey;
+    size_t mackeylen;
+    unsigned char macval[20];
+    char *otrmsg = NULL;
+    DataMsg datamsg;
+    size_t textlen;
+    unsigned int offset;
+    const unsigned char *old_text, *new_text;
+    char *newdatamsg;
+    size_t i;
+
+    if (argc != 5) {
+	usage(argv[0]);
+    }
+
+    argv_to_buf(&mackey, &mackeylen, argv[1]);
+    if (!mackey) {
+	usage(argv[0]);
+    }
+
+    if (mackeylen != 20) {
+	fprintf(stderr, "The MAC key must be 40 hex chars long.\n");
+	usage(argv[0]);
+    }
+
+    textlen = strlen(argv[2]);
+    if (textlen != strlen(argv[3])) {
+	fprintf(stderr, "The old_text and new_text must be of the same "
+		"length.\n");
+	usage(argv[0]);
+    }
+    old_text = (const unsigned char *)argv[2];
+    new_text = (const unsigned char *)argv[3];
+
+    if (sscanf(argv[4], "%u", &offset) != 1) {
+	fprintf(stderr, "Unparseable offset given.\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);
+    }
+
+    /* 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 MAC key?\n");
+	exit(1);
+    }
+
+    /* Modify the ciphertext */
+    for(i=0; i<textlen && offset+i < datamsg->encmsglen; ++i) {
+	datamsg->encmsg[offset+i] ^= (old_text[i] ^ new_text[i]);
+    }
+
+    /* Recalculate the MAC */
+    newdatamsg = remac_datamsg(datamsg, mackey);
+    printf("%s\n", newdatamsg);
+    free(newdatamsg);
+
+    free_datamsg(datamsg);
+    free(mackey);
+    fflush(stdout);
+    return 0;
+}