DSA2

[Carlo Luciano Bianco]

Il /27 set 2006/, *Robert J. Hansen* ha scritto:

> Carlo Luciano Bianco wrote:
>> Needless to say, I completely agree with both you and Werner on
>> this. This discussion about "balancing" security is very
>> interesting [at least for me... ;-)] from a theoretical point of
>> view. I know very well that using this extra-large keys does not
>> add any security in real life. 
> 
> There's a contrary view, which says that balancing cryptosystem
> components is an unnecessary distraction.  This contrary view says
> that each component of a system should be built to meet or exceed
> security requirements while meeting or exceeding performance and
> usability requirements.  As long as each component is in that
> sweet spot, then you're great.

I agree with David in saying that this two points of view are not
necessarily "contrary" to each other. You can chose a "minimum"
security level and then make sure that all cryptosystem components
are "balanced" in the sense that they all meet at least such level. 

This is also because the "equivalence" between the security of a
DSA/RSA 15-kbit key, SHA-512 and AES-256 comes just from a more or
less rough estimate and not from a mathematical theorem (AFAIK).
Therefore, if you "overshoot" the security of a component of your
cryptosystem, this is not bad. At worst, it is not even good (i.e.
it is useless), but for sure it is not bad. 

Just to make an example:

I am currently using a 4096-bit RSA key, with AES-256 and SHA-512 as
"preferred" algorithms. I am not going to switch back to AES-128 and
SHA-256 to have a "balanced" system. I will stay with AES-256 and
SHA-512, even if they are estimated to be much more secure than
4096-bit RSA keys (and therefore maybe "useless"). In this way, I
can be reasonably sure that the weakest component of my cryptosystem
is the 4096-bit RSA key. But such a key meets my minimum security
requirements, so I am safe. 

The "balance" requirement for my cryptosystem means that I will
bother GnuPG developers about adding full support for longer public
keys before bothering them about longer symmetric keys and longer 
hashes, instead of viceversa... ;-)

-- 
                      |  ICQ UIN: 109517158
 Carlo Luciano Bianco |  Home page: <http://clbianco.altervista.org/>
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GnuPG RSAv4 4096 - Fingerprint:FA68CF697EA63865AAFA805F68703AD40609D743