Re: and now for something complete different part 2

Valery Pryamikov wrote:
Antony Clements wrote:
No wrong.

CFB is a chaining mode for BLOCK CIPHERS, not STREAM CIPHERS.

irrespective that someone has already said that CFB mode will work on any
block size, even if the block is 1 in size, and also nevermind that a block
cipher is just a stream cipher that is broken up into manageable chunks. in
other words almost any mode in a block cipher will also work in a stream
cipher because each byte is treated as a block. but i know nothing of
anything so who would ever have an intelligent conversation about something
so that i can learn things.

WOW, THAT'S FUNNY!
Not only *you do not even read what have been said to you*, but *you
also falsely accuse people that was trying to explain you some very
basic things in claiming something that is apparently wrong*...
THAT IS ONE OF THE MOST TROLLISH THINGS! AND ONE OF THE BEST INDICATION
OF TROLL IN THE GROUP!

What have been said to you is that stream cipher operates on bits, (not
bytes as you claimed). Stream cipher's key stream could be modeled as
PRF.
OFB, CBC, CFB ... and all other block cipher's modes operations require
a PRP (and not some commutative bit-operation with output of PRF). In
other words: CFB only works for Block Ciphers (PRP)!
Stream ciphers are really different than block ciphers!
What was also said to you was that there are known techniques of
building block ciphers out of any PRF (i.e. from stream cipher) - by
using PRF with generalized Feistel transformation. That way you can use
your stream cipher as a part of round transform of the completely new
block cipher... which you can use afteward with block cipher modes of
operations. However, by doing that you'd need even larger block sizes
than traditional block ciphers, just to keep up with security.
And btw. the ability of using stream ciphers to build block ciphers
(and vise versa) doesn't matter when we think about differences and
similarities of block ciphers and stream ciphers! They are different!
The thing that they really share is a word "cipher" in the name...

-Valery.
http://www.harper.no/valery

I suspect that you aren't going to read long answer, so here is a
shorter explanation:

It is possible to build Hash out of Ciphers as well as it is possible
to build Ciphers out of Hash. Does it mean that they are the same?
NO! They are different!

analogously:

It is possible to build Stream Cipher out of Block Ciphers and vice
versa. Does it mean that they are the same?
NO! They are different!

You will never learn if you don't read... stop bullshitting yourself
that you learn by trying and failing - that way you'll only guaranteed
to fail.

-Valery.
http://www.harper.no/valery

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