Re: Key entropy, stream entropy, block entropy, block population entropy AKA uniique stream length

On 2007-02-07, jt64@xxxxxxxx <jt64@xxxxxxxx> wrote:
On 5 Feb, 23:26, rossum <rossu...@xxxxxxxxxxxx> wrote:
On 5 Feb 2007 09:36:28 -0800, j...@xxxxxxxx wrote:

I said that the "BLOCK ENTROPY" within a cipher AKA the way to create
a UNIQUE block by downmixing internal streams in a cipher can exceed
the keyentropy.

Then how can you decrypt a message? If the block entropy exceeds the
key entropy, then given the key the receiver cannot decide which of
the possible blocks the key can generate is the correct block to
decrypt with.

rossum

Keyexpanded shuffles/permuation ciphers are not key to block 1:1
ciphers.
They are key to stream 1:1 ciper

So there is really no problem, you have to know where you are in the
permutation cycle for the key that is all.

Then that's all an attacker needs to know to decrypt it too.

How do you communicate this information to the other end without telling
the attacker? (Hint: if you do it secretly, it's essentially part of
the key)

--
David Taylor
.

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