[NEWS] Cisco VPN Client Password Decryption

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Cisco VPN Client Password Decryption
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SUMMARY

The Cisco VPN Client uses weak encryption to store user and group
passwords in your local profile file.

DETAILS

The main problem of the method used to encrypt the passwords is, that the
whole procedure is deterministically and no user input is used. This
effectively means that the encryption keys the Cisco Client calculates can
also be calculated by any other program whensoever this program knows the
algorithm. This algorithm was now reversed.

The algorithm:
The algorithm which is used to encrypt a given user/group password is
shown below (for further details just visit the source code):
* The current date as a string is retrieved (e.g. Mon Sep 19 20:00:00
2005)
* Then a SHA-1 Hash h1 is computed (20 Bytes)
* h1 is modified and a new Hash h2 is calculated
* h1 is again modified and h3 is calculated
* the 3DES key is made of h2 and the first 4 bytes of h3
* The password is encrypted using 3DES in CBC Mode. The IV consists of
the first 8 Bytes from h1.
* The algorithm computes a last hash h4 from the encrypted pasword
* The key enc_UserPassword in our profile file now looks like ths:
h1|h4|encrypted password

The Cisco Password Revealer along with the source code can be found
<http://www.evilscientists.de/blog/?dl=CiscoPasswordRevealer.rar> here.

ADDITIONAL INFORMATION

The original article can be found at:
<http://evilscientists.de/blog/?page_id=343>
http://evilscientists.de/blog/?page_id=343

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