On Fri, Jun 30, 2006 at 07:19:39AM -0400, Victor Duchovni wrote:
> On Thu, Jun 29, 2006 at 12:28:44PM -0700, Chris Clark wrote:
>
> > I have written a client program in which I allow the user to configure
> > which cipher groups they want to allow as well as a cipher strength of
> > low, medium, or high.
> >
> > The problem is I can't find a way of selecting the order in which I
> > want the cipher negotiated. For example if all ciphers are enabled in
> > the configuration, I would perfer if AES is selected during
> > negoitation.
>
> What real problem is this intended to solve?
>
> > Currently I specify the group (HIGH/MEDIUM/LOW) and remove some ciphers
> > from a group (IDEA and ADH). I also remove AES at the beginning (Shif
> > +="-AES:") and add it later because if I don't remove AES there is no
> > way to separate AES128 and AES256.
> > (Due to an OpenSSL bug, HIGH selects both AES128 and AES256)
>
> Is this a real problem? What's wrong with:
>
>
> !EXPORT:!LOW:!MEDIUM:DEFAULT:-DHE-RSA-AES128-SHA:-DHE-DSS-AES128-SHA:-AES128-SHA
>
Sorry, I guess this ("DEFAULT:" should have been first) does not work,
because removing the 128 bit ciphers also removes the 256 bit ciphers.
With:
$ openssl ciphers -v \
'DHE-RSA-AES128-SHA:DHE-DSS-AES128-SHA:AES128-SHA:@STRENGTH'
DHE-RSA-AES256-SHA SSLv3 Kx=DH Au=RSA Enc=AES(256) Mac=SHA1
DHE-DSS-AES256-SHA SSLv3 Kx=DH Au=DSS Enc=AES(256) Mac=SHA1
AES256-SHA SSLv3 Kx=RSA Au=RSA Enc=AES(256) Mac=SHA1
DHE-RSA-AES128-SHA SSLv3 Kx=DH Au=RSA Enc=AES(128) Mac=SHA1
DHE-DSS-AES128-SHA SSLv3 Kx=DH Au=DSS Enc=AES(128) Mac=SHA1
AES128-SHA SSLv3 Kx=RSA Au=RSA Enc=AES(128) Mac=SHA1
and
$ openssl ciphers -v \
'DHE-RSA-AES256-SHA:DHE-DSS-AES256-SHA:AES256-SHA:@STRENGTH'
DHE-RSA-AES256-SHA SSLv3 Kx=DH Au=RSA Enc=AES(256) Mac=SHA1
DHE-DSS-AES256-SHA SSLv3 Kx=DH Au=DSS Enc=AES(256) Mac=SHA1
AES256-SHA SSLv3 Kx=RSA Au=RSA Enc=AES(256) Mac=SHA1
DHE-RSA-AES128-SHA SSLv3 Kx=DH Au=RSA Enc=AES(128) Mac=SHA1
DHE-DSS-AES128-SHA SSLv3 Kx=DH Au=DSS Enc=AES(128) Mac=SHA1
AES128-SHA SSLv3 Kx=RSA Au=RSA Enc=AES(128) Mac=SHA1
producing the same results you are out of luck, if you want 256 bit AES,
you always also get 128 bit AES. In practice (SSLv3/TLSv1) this is not a
problem, because the client and server always choose the strongest common
cipher.
--
Viktor.
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