[cryptography] The Unbreakable Cipher

Jonathan Katz jkatz at cs.umd.edu
Wed Sep 25 15:51:12 EDT 2013

On Wed, Sep 25, 2013 at 1:30 PM, Greg Rose <ggr at seer-grog.net> wrote:

> On Sep 25, 2013, at 9:40 , Jonathan Katz <jkatz at cs.umd.edu> wrote:
> > "Every cipher is breakable, given enough traffic": in principle, yes, as
> long as the traffic (formally, the entropy of the traffic) is larger than
> the key length.
> You misstated this. It's breakable if the *redundancy* of the traffic is
> larger than the key length.

Not so; this is most easily seen by taking the uniform distribution over
n-bit messages, in which case the entropy is n and the redundancy is 0.

> regards,
> Greg.
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