[Cryptography] Terakey, An Encryption Method Whose Security Can Be Analyzed from First Principles

[Peter Fairbrother]

On 13/07/2020 16:43, Arnold Reinhold via cryptography wrote:
> Terakey(tm) is a cipher that offers confidentiality properties provable 
> from first principles. It employs a shared secret key substantially 
> larger than the anticipated volume of message traffic. 

Ie an OTP.

Key bytes are
> extracted pseudo-randomly from the large key, using a message indicator 
> as the seed. 

What is the advantage of the pseudo-random selection? That two stations 
can use the terakey using some secret shared-to-them-only key to the 
PRNG without any other stations seeing that traffic? [3]

Well we know that the other stations know the secret terakey, so as far 
as they are concerned the problem is reduced to breaking the PRNG.

That may be a little harder because of the added (I presume) XOR with a 
selection from the OTP, as some methods may not work; but it is not 
necessarily any harder.

And having multiple stations all in possession of the same secret 
terakey is a huge single point of failure - the probability of a 
secret's compromise is, inter alia, proportional to the square of the 
number of people who know it. [8]


Two messages can occasionally use the same
> key byte, violating the one-time use restriction. That risk can be 
> quantified and various ways are proposed to deal with it.

So how do you analyse that? Just probability of collisions? If that's 
all, who's to say the pseudo-random generator doesn't kick out 
collisions at a more-than-random rate, or in some pattern? You have to 
analyse the PRNG as well.

And if you then have a cryptographically secure PRNG ...



Going from the provably-secure OTP to analysable (if it is analysable, 
which I doubt) doesn't seem like much of a gain.



Peter Fairbrother

[3] that doesn't seem to be in your proposal, but I am assuming. If it 
isn't then I see no advantage - bookeeping is reduced to "don't reuse 
key" and if eg a part of the terakey is allocated to station 1 the 
station just uses the next portion of its part for sending its next message.

[8] fourteenth law.