Re: ARJ encryption

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Article #2611

#2611

From: Ralph Wirthlin
Date: Wed, 30 Dec 1992 14:55

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rwirthli@nyx.cs.du.edu (Ralph Wirthlin) writes:

>	I was wondering if anyone knows the algorithm used in arj for
>the encryption scheme.  It appears to XOR the compressed text with some
>permutation of the password string (I suspect this is XOR'd with something
>else as well).  If anyone knows, please email and I'll summarize, otherwise
>I'll just figure it out myself.

Thanks to all those who responded.  I was able to figure out how ARJ does 
it's encryption.  It was simpler than I suspected.  ARJ adds a single
byte constant to each character in the password and then does an XOR
with this new password to generate the encrypted, compressed file.
  I suspect that this constant is generated from the system clock, but
that doesn't really matter, since ARJ stores this constant in the
local file header at offset 0xb.

					Ralph

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Message-ID: <1992Dec30.145541.8530@mnemosyne.cs.du.edu>

Path: arc1-ca.pugleaf.net!sparky!uunet!mnemosyne.cs.du.edu!nyx!rwirthli

References: <1992Dec28.211703.12276@mnemosyne.cs.du.edu>

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Newsgroups: sci.crypt,comp.binaries.ibm.pc.d
Path: arc1-ca.pugleaf.net!sparky!uunet!mnemosyne.cs.du.edu!nyx!rwirthli
From: rwirthli@nyx.cs.du.edu (Ralph Wirthlin)
Subject: Re: ARJ encryption
Message-ID: <1992Dec30.145541.8530@mnemosyne.cs.du.edu>
Sender: usenet@mnemosyne.cs.du.edu (netnews admin account)
Organization: University of Denver, Dept. of Math & Comp. Sci.
References: <1992Dec28.211703.12276@mnemosyne.cs.du.edu>
Date: Wed, 30 Dec 92 14:55:41 GMT
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