----- Original Message ----- From: "Travis H." <[EMAIL PROTECTED]>
Subject: semi-preditcable OTPs
Despite [flawed OTPs], the NSA wasn't able to crack any messages.

My question is, why?   I think I know the reason, and that is that any
predictability in a symbol of the OTP correlated to a predictability
in only one plaintext symbol.  In other words, there was no "leverage"
whereby that plaintext could then be used to derive other symbols.
Can anyone explain this better (or more accurately)?  Is this lack of
diffusion?  Or does it have something to do with the unicity distance?

You've pretty much got it. In order for a OTP to work you simply need what I commonly refer to as an overflow of entropy. The source of this entropy doesn't matter and it can be from the plaintext as much as it can be from the key. This extends the unicity distance (as you noted) and can render it impossible to decrypt. Joe

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