Re: Is RC4 a good choice?

From: Tom St Denis (tomstdenis_at_iahu.ca)
Date: 08/05/03 

Date: Mon, 04 Aug 2003 23:10:50 GMT

Mrsjunecarey wrote:
>>Subject: Re: Is RC4 a good choice?
>>From: mdw@nsict.org (Mark Wooding)
>>Date: 8/1/03 5:22 PM GMT Daylight
>
>
>>It's an /enormous/ code book.
>>
>
>
> Yeh but it's still a code-book.
> And it still sucks.

Science practices like this only make me wonder how civilization is
surviving this long.

>>Why's what a problem? There's nothing which says that a message has to
>>be a whole number of blocks in length, for example. Consider modes such
>>as CBC-with-stealing, CFB, OFB, OCB, etc.
>>
>
>
> It's inconvenient.

Ciphers can also be used as hashes. [or hashes as ciphers!]. Stream
ciphers are mostly only useful as ciphers

Also if you cannot encapsulate a cipher in CTR mode you shouldn't be
writing software.

>>Of course, stream ciphers are always trivial objects. Compare AES or
>>Blowfish with SEAL, for example.
>
>
> SEAL uses a cryptographic hash function which means it sucks very badly; almost
> as bad as a block-cipher, but not quite.

And your cipher uses horribly jibberish non-portable C++ code. Yea, way
to chalk one up for your argument.

BTW RC5 is a block cipher that is WAY simpler than Lxy.

>>[theory lesson deleted]
>>
>>Counter mode turns a PRF into a PRG. Thus, a block cipher in counter
>>mode /is/ an additive stream cipher.
>
>
> Wrong.
>
> A block cipher in counter mode is just a block cipher in counter mode.
>
> It is only becomes a binary additive stream cipher when you XOR its output with
> some plaintext.

Um, what did you think you did with the key stream? Same thing for L14,
I could use it as a PRNG [I wouldn't but I could] which means it
wouldn't be an additive stream cipher.

>>A professional should know the things I've described above, and in the
>>formal terms used in the literature rather than the watered-down
>>handwaving I've used above.
>>
>
>
> You're assuming that when I said "professional" I was meaning "professional
> cryptographer".
>
> And I never said that.

Well as an auto salesman you're still not that convincing!

Tom

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