bugtraq - Ciscos VPN-Client-Passwords can be decrypted

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Message-ID: <778522901.20051016212841@Sniff-em.com>
Date: Sun, 16 Oct 2005 21:28:41 +0200
From: Thierry Zoller <Thierry@...ff-em.com>
To: full-disclosure@...ts.grok.org.uk
Cc: bugtraq@...urityfocus.com
Subject: Ciscos VPN-Client-Passwords can be decrypted

Dear List,

[1] heise published a news article today.
[2] EvilScientists reverse engineered the algorithm Cisco uses to _obscufate_ the
    passwords.
[3] PoC

Summary :
Cisco uses 3des to encrypt the passwords, however it does so using
a deterministic encryption sheme (no user input) and thus must be
reproducible.

The algorithm [2] found was as follows :

* GetDate - convert to string
* Generate an SHA Hash from that string h1 (20 Bytes)
* h1 is modified into Hash h2
* h1 is modified into Hash h3
* h2 and the first 4 Bytes from h3 give the 3DES Key
* The clear text password no encrypted in 3DES CBC Mode. The IV is the first 8 Bytes of h1.
* If the size of the clear text password is not a multiple of the
  Block size, the differece to the next block is calculcated and padded
  with a Digit. -> length of password is known
* A last hash is calculated from the encrypted Password h4
* The value of the Key enc_UserPassword is: h1|h4|verschlüsseltes Passwort

Credits:
[1] http://www.heise.de/newsticker/meldung/64954
[2] http://evilscientists.de/blog/?page_id=339
[3] http://www.evilscientists.de/blog/?dl=CiscoPasswordRevealer.rar
I take no credit I am only translating and forwarding.

-- 
Thierry Zoller
http://thierry.sniff-em.com

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