Re: Stream cipher against block cipher

From: Tom St Denis (tomstdenis_at_iahu.ca)
Date: 06/27/03 

Date: Fri, 27 Jun 2003 14:33:15 GMT

azamruk wrote:

> Hi,
>
> Is secret key stream cipher are globally weaker than block cipher ?

I'll take a wild stab at guessing you're not an English speaker per
default....

Yes, for the most part most stream cipher algorithms [rc4, seal, etc]
are weaker than their block cipher counterparts [in CTR mode for comparison]

> Why the most popular secret key algorithms are block cipher ?

This doesn't follow. You asked if stream ciphers are weaker than block
ciphers than asked why block ciphers are popular?

> Is there weekness in them (stream cipher) or difficulties to make them strong ?
> Or is it only a "culture" biasis ?

The big issue is most stream ciphers cut corners to get a speed
advantage. RC4 can emit key stream bytes at close to 4 cycles per byte
whereas the best AES implementations are [if I recall correctly] around
16 cycles per byte. [on x86 platforms].

Block ciphers in CTR mode involve more work than algorithms like SEAL
and RC4.

Tom 

--
LTC: http://libtomcrypt.org
LTM: http://math.libtomcrypt.org
The Book: http://book.libtomcrypt.org

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