userids and subkeys

[Dennis Lambe Jr.]

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On Sat, 2003-08-09 at 16:52, Dreweke Alexander wrote:
> What exactly is the primary public key is it the DSA key which is used
> to sign messages or is it ElGamal key for the encryption? Do i have to
> create new just DSA or ElGamal subkeys or both? As far as i understand
> the manual it i just advisable to rotate the encryption (ElGamal) key,
> which seems reasonable, but would it also make sense to rotate the DSA
> key?

The primary key is the DSA key.  the ElGamal key is a subkey attached to
it.  It's generally considered much more important to change your
encryption subkey occasionally than to change your signing key.  Here's
why:

If someone is capable of breaking public key cryptography, they can use
that to do two things:

1) Read your messages
2) Masquerade as you

If someone is successfully decrypting your messages surreptitiously, you
have no real way of knowing.  However, if someone is masquerading as
you, they're leaving evidence all over the place which, with a high
degree of probability, will get back to you eventually.

If you have evidence that there is a party capable of masquerading as
you, that means you have evidence that there is a party capable of
breaking public key cryptography for either of the 2 purposes outlined
above.  Once you present that evidence, people will seek out and switch
to more secure forms of communication.  This is not in the best
interests of the party with the public key cracking technology.

All of this means that, as unlikely as it is (and it is very unlikely)
that someone has compromised your encryption subkey, it is much more
unlikely that someone has bothered to compromise your primary signing
key.  It's just much more valuable to keep cracking technology secret
than to broadcasting it through identity theft.

That's what I've read, however.  If any security experts on the list
would like to correct me, I'd invite them to.

--Dennis Lambe

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