Saturday, September 3, 2011

Vigenère cipher

If I run into a password that's been encrypted with the Vigenère cipher and don't care to download a tool or use an online decryptor, here's a quick solution I can use to see what that password is.

Let's say the password I'm wanting to uncover is an NTP authentication key. For instance:

R1#show run | include authentication-key
ntp authentication-key 1 md5 060506324F41 7

Where 060506324F41 is the key I'd like to know the password for.

I create a key chain on the router and paste in the ciphered password:

R1#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
R1(config)#key chain TEST
R1(config-keychain)#key 1
R1(config-keychain-key)# key-string 7 060506324F41

Follow it up with show key chain TEST:

R1#show key chain TEST
Key-chain TEST:
    key 1 -- text "cisco"
        accept lifetime (always valid) - (always valid) [valid now]
        send lifetime (always valid) - (always valid) [valid now]

There you have it. In my case, the password is cisco.


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