Decrypt Cisco Passwords

If `service password-encryption` is not configured on the Cisco device, you can simply read the plain text passwords from the configuration file.

If `service password-encryption` is configured on the Cisco device, most of the passwords are encrypted using a weak encryption algorithm (Type 7) which is trivial to decrypt. If you have access to the Cisco's configuration file, you can still decrypt the passwords fairly easily.

`service password-encryption` is enabled using the following command:

FAQ-Cisco (config)#service password-encryption

Network administrators often store IOS configuration files on TFTP (Trivial File Transfer Protocol) servers. On one server, you may find configuration files for every Cisco device on the network.

Cisco uses two encryption methods to secure IOS passwords. The first, type 7, uses a Cisco proprietary weak encryption algorithm. The second, type 5, uses strong MD5 encryption.

Cisco Type 7 passwords

If you see a password in the configuration file with a '7' in the second to last field, that password is encrypted using Cisco's weak proprietary algorithm. For example:

enable password 7 03003E2E05077C4F4007

There are many programs available to decrypt Cisco type 7 passwords.

Here is a small PERL program to decrypt Cisco type 7 passwords:

#!/usr/bin/perl -w

# $Id: ios7decrypt.pl,v 1.1 1998/01/11 21:31:12 mesrik Exp $

#

# Credits for original code and description hobbit@avian.org,

# SPHiXe, .mudge et al. and for John Bashinski

# for Cisco IOS password encryption facts.

#

# Use of this code for any malicious or illegal purposes is 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;

Cisco Type 5 passwords

Enable secret passwords are hashed using the MD5 (Message Digest 5) algorithm instead of the weak Cisco proprietary algorithm. Enable secret passwords are not trivial to decrypt.

An "enable secret" password is configured using the following command:

FAQ-Cisco (config)#enable secret password

If you see a password in the configuration file with a '5' in the second to last field, that password is hashed using the MD5 algorithm. For example:

enable secret 5 $1$B8pH$PmmcMRoqfeEtQ7WxL865a0

Although MD5 is a strong algorithm, it may still be attacked with a dictionary attack or a brute force attack.