Re: Stream Ciphers and Confusion/Diffusion

From: flip (flip_alpha_at_safebunch.com)
Date: 01/09/05 

Date: Sat, 8 Jan 2005 16:39:57 -0800

"Douglas A. Gwyn" <DAGwyn@null.net> wrote in message
news:xt2dnVhXWOo5y33cRVn-rQ@comcast.com...
> flip wrote:
> > since stream ciphers are a subset of block ciphers (symmetric ciphers),
>
> Wrong. Stream ciphers are not a subset of block ciphers.

Interesting, they are classified as such in AC2 and on the RSA FAQ (unless I
am really confused about how I read their respective statements).

I have also seen this classification in several other books.

Lastly, I thought the stream ciphers could also act on bytes at a time (just
something less than what a block cipher might be used for). This is why I
thought I understood the classificatiion.

>
> > So, is it possible to define these terms [confusion and diffusion]
> > for both synchronous and asynchronous stream ciphers?
>
> They're not precisely defined terms, and they do apply
> (such as they are) to all ciphers. Some ciphers might
> not exhibit much of one or the other..
>
> > What are the general rules/thoughts for using stream ciphers over block
(or
> > using a block cipher as a stream cipher) and their respective security
> > properties (seems like they are less well understood than block ciphers
> > are).
>
> There are no general rules, but if you need to transmit
> unit smaller than a block as soon as the input data is
> available, you must use a stream cipher, even if you
> have to cobble one together from block-cipher components.
>
> True stream ciphers have received much less attention
> in the open cryptologic community.

Relevant Pages

  • Re: Sun setting on stream ciphers?
    ... > with the title 'RSA Panel: Cryptography Can't Foil Human ... > on stream ciphers used to encode real-time data streams. ... > depend on the 'definition' of stream cipher and block cipher. ...
    (sci.crypt)
  • Re: Sun setting on stream ciphers?
    ... > with the title 'RSA Panel: Cryptography Can't Foil Human ... > on stream ciphers used to encode real-time data streams. ... > depend on the 'definition' of stream cipher and block cipher. ... It's true that most recent designs are actually PRP ...
    (sci.crypt)
  • Re: Sun setting on stream ciphers?
    ... > Stream ciphers are more efficient in terms of bandwidth, ... > don't need padding bits. ... > block cipher for VoIP? ...
    (sci.crypt)