Matthias Loepfe wrote:
>
> Hi again,
>
> Does really NOBODY has anything to say about the following? Shouldn't the server
> try to always choose the best available cipher?
>
> regards
>
> Matthias
>
> Matthias Loepfe wrote:
> >
> > Hi
> >
> > I have fundamental question regarding choosing the chipher in SSL. The spec
> > says that the client send the accepted ciphers in the order of preference, and
> > that the server chooses then the cipher to use.
> >
> > In the current implementation of ssl3_choose_cipher() it is realy the client's
> > preference which will be take to choose from the common ciphers.
> >
> > But I know many companies which would like to be able to set the preference
> > on the server side.
> >
> > Because of the current behaviour the 'RC4-MD5' will be choosen before
> > 'DES-CBC3-SHA' which I think is not correct.
> >
> > Now the questions: 1) Is (from the spec point of view) the server side allowed
> > to choose according to his own preferences?
> > 2) Why should the server not enforce his own preference?
> >
As you point out the SSL 3 spec says the client gives a list of ciphers
in order of preference and then says the server has to decide which to
use.
I can't see any specific reason why the server can't enforce its own
preference but currently this can only be done AFAIK by disabling the
ciphers altogether and risking a handshake failure.
RC4 is often chosen over 3DES for speed reasons.
In terms of strength it depends on the interpretation: with sufficient
resources 3DES has an effective key size of 112 bits (due to the meet in
the middle attack) whereas RC4 is a maximum of 128.
Steve.
--
Dr Stephen N. Henson. http://www.drh-consultancy.demon.co.uk/
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