Which type of key should I choose and why?

[L. Sassaman]

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On Mon, 16 Oct 2000, Paul L. Allen wrote:

> That's what I gathered.  At a guess, in the first DSA is taking the
> place of MD5 from the original with EG in the RSA role and in the
> other option EG is being used both for encryption and cryptographic
> hashing.  But I've yet to find anything confirming that guess or
> saying why one is preferable to the other.

Nope, SHA-1 is taking the place of MD5.

DSA is taking the place of RSA for signing, and ElGamal is taking the
place of RSA for encryption.

RFC 2440 has the gorey details.
 
> Good thinking.  That's certainly a good point.  Using EG for both
> functions would therefore presumably mean either accepting weaker
> signing or more time-consuming encryption.  But that's a pure guess
> which may be wrong.  Basically, this is a weak-spot in the docs because
> users shouldn't have to puzzle it out for themselves or make guesses.
> It's as intrinsic to correct operation as choosing the right key size
> and that is covered in detail.

Phil Zimmermann calls DSA "ElGamal debugged". There's academic attacks
against ElGamal signatures. Don't use it for signing.
 
> I noticed.  But I don't know if EG got added to PGP because of technical
> superiority or to evade the patent difficulties that made it such a
> hassle to ensure you were using it legally.  So I don't know if I should
> be using EG or RSA for encryption strength now that GPG offers both.

It was mainly licensing issues that prompted the use of DSA/ElGamal in PGP
3. (Later renamed PGP 5.)

But it was a convenient excuse to revisit the PGP key format, and develop
v4 keys which added more functionality and versatility in features.
 
> > but will only generate ones using version 4 packet formats, not the older
> > version 3 packets. Given the advantages of v4 keys I think that's
> > understandable.
> 
> Trouble is, one of the reasons I'm looking at GPG is for use with
> automated verification systems used by various domain registrars.
> They use PGP but don't say what version.  I know I can get RSA and
> (somewhat dubiously) IDEA but I still don't know if that's enough to
> interoperate with what those registries are using.  Or maybe DSA/EG is
> enough but the packet format will cause me problems.

I think there needs to be better v3 key support. Whether or not GnuPG
generates v3 keys, it needs to be able to utilize them.
 
> > There's also module implementing the AES selection, Rijndael,
> > already...
> 
> So I noticed, although I hadn't realized that was the AES selection.  To
> be honest, if they're happy with it, I'm not, given the political
> constraints they probably operated under...

That makes no sense.

But, for what it's worth, I met the Rijndael authors today, and they
looked quite happy. :)

__

L. Sassaman

Security Architect             |  "Lose your dreams and you
Technology Consultant          |   will lose your mind."
                               |   
http://sion.quickie.net        |       --The Rolling Stones


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