The symmetric ciphers

[Werner Koch]

On Wed, 30 Oct 2013 20:25, pkk at spth.de said:

> If we have plenty of randomness available, we could do this a

Entropy (which should be at the core of every CRNG) is a scarce
resource.  Thus a one time pad is not going to work because you need
true random at the same size of the message.

> XOR the message M with a random one-time pad P to obtain N. Encrypt P
> with A, and N with B.
> The drawback is that this doubles the lenth of the message.

And that you need a way to securely convey the OTP to the recipient.

The soviets had severe problems to do that during WWII and later and
resorted to double use the one time pads.  That was one of the origins
of the UKUSA alliance aiming and succeeding at breaking there messages
(project VENONA).


Shalom-Salam,

   Werner

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