From: "Mark M." <markm@voicenet.com>
Date: Fri, 18 Oct 1996 13:47:10 -0700 (PDT)
To: trei@process.com>
Subject: Re: POTP critques?
In-Reply-To: <199610181356.GAA10935@toad.com>
Message-ID: <Pine.LNX.3.95.961018163224.621A-100000@gak.voicenet.com>
MIME-Version: 1.0
Content-Type: text/plain


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On Fri, 18 Oct 1996, Peter Trei wrote:

> I'm looking for independent critiques of the system, something
> better than 'it's not really a one-time pad.' Is the cryptosystem
> which is actually implemented worth a damn? Does their claim
> to have solved the key distribution problem hold water? I
> seem to remember something about them wanting to
> generate keys for you, and ship them to the customer. Is this
> correct?

POTP is a stream cipher where the key is derived from a "state" and bits from
the ciphertext chosen using the current state.  Two machines have to
synchronize their states before encryption can take place.  The key is derived
from a one-way function performed on the state.  This really doesn't solve the
key distribution problem because initial synchronization has to take place on
a secure channel.  The current state also has to be saved on each machine.
I think the "escrow" system you are referring to is some other encryption
program.

Elementrix does acknowledge that they have a stream cipher and don't refer to
it as a one-time pad.  The only reason OTP is in the name is that the key
derived from the state is as long as the ciphertext being encrypted.  They
claim that the state is larger than the key and it is computationally
infeasible to derive the state given the key.  I would guess that the size of
the next state is determined by the size of the plaintext to be encrypted.

As for security of the system, I really don't know.  Their algorithm is
proprietary so I would avoid it for that reason alone.  They have not yet
gotten any comments regarding security from any cryptographers.  The entire
security of this system is based upon the algorithm used to generate the state
from a previous state and the one-way function used to generate the session
key.  Unless they are using a hash algorithm like SHA-1 to generate the keys
and states, I would seriously question the security of it.

Mark
- -- 
finger -l for PGP key
PGP encrypted mail prefered.



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