AES128 or AES256 by default?

Paul Querna chip at
Thu May 15 18:12:50 CEST 2008

On Thu, May 15, 2008 at 2:34 AM, Simon Josefsson <simon at>

> There is a debian bug:
> Which asks that we make AES-256 the default preferred cipher.  Right now
> AES-128 is the default preferred cipher.  Of course, today AES-256 is
> supported as well (it is the second preferred default cipher).
> What do people think here?

Applications can expose a cipher priortity configuration option -- just as
mod_gnutls does -- and then you could configure dovecot to default to

I don't believe the concerns expressed in the debian bug should be a reason
to have libgnutls's default priorities changed.


> I don't care strongly, but I find the arguments for AES-256 rather weak.
> According to RFC 3766, to match a 256 bit symmetric key size, you need a
> ~15kb large RSA key or a ~500b large DSA key.  People don't use that
> kind of public key sizes today as far as I know, as they become very
> big.  The few who do should be able to tweak the GnuTLS cipher
> preference accordingly.
> /Simon
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