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/* crypt.c - TACACS+ encryption related functions
*
* Copyright (C) 2010, Pawel Krawczyk <pawel.krawczyk@hush.com> and
* Jeroen Nijhof <jeroen@jeroennijhof.nl>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* 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 - see the file COPYING.
*
* See `CHANGES' file for revision history.
*/
#include "libtac.h"
#include "xalloc.h"
#include "md5.h"
/* Produce MD5 pseudo-random pad for TACACS+ encryption.
Use data from packet header and secret, which
should be a global variable */
u_char *_tac_md5_pad(int len, HDR *hdr) {
int n, i, bufsize;
int bp = 0; /* buffer pointer */
int pp = 0; /* pad pointer */
u_char *pad;
u_char *buf;
MD5_CTX mdcontext;
/* make pseudo pad */
n = (int)(len/16)+1; /* number of MD5 runs */
bufsize = sizeof(hdr->session_id) + strlen(tac_secret) + sizeof(hdr->version)
+ sizeof(hdr->seq_no) + MD5_LEN + 10;
buf = (u_char *) xcalloc(1, bufsize);
pad = (u_char *) xcalloc(n, MD5_LEN);
for (i=0; i<n; i++) {
/* MD5_1 = MD5{session_id, secret, version, seq_no}
MD5_2 = MD5{session_id, secret, version, seq_no, MD5_1} */
/* place session_id, key, version and seq_no in buffer */
bp = 0;
bcopy(&hdr->session_id, buf, sizeof(session_id));
bp += sizeof(session_id);
bcopy(tac_secret, buf+bp, strlen(tac_secret));
bp += strlen(tac_secret);
bcopy(&hdr->version, buf+bp, sizeof(hdr->version));
bp += sizeof(hdr->version);
bcopy(&hdr->seq_no, buf+bp, sizeof(hdr->seq_no));
bp += sizeof(hdr->seq_no);
/* append previous pad if this is not the first run */
if (i) {
bcopy(pad+((i-1)*MD5_LEN), buf+bp, MD5_LEN);
bp+=MD5_LEN;
}
MD5Init(&mdcontext);
MD5Update(&mdcontext, buf, bp);
MD5Final(pad+pp, &mdcontext);
pp += MD5_LEN;
}
free(buf);
return pad;
} /* _tac_md5_pad */
/* Perform encryption/decryption on buffer. This means simply XORing
each byte from buffer with according byte from pseudo-random
pad. */
void _tac_crypt(u_char *buf, HDR *th, int length) {
int i;
u_char *pad;
/* null operation if no encryption requested */
if((tac_secret != NULL) && (th->encryption == TAC_PLUS_ENCRYPTED_FLAG)) {
pad = _tac_md5_pad(length, th);
for (i=0; i<length; i++) {
*(buf+i) ^= pad[i];
}
free(pad);
} else {
TACSYSLOG((LOG_WARNING, "%s: using no TACACS+ encryption", __FUNCTION__))
}
} /* _tac_crypt */
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