Re: proposed PGP mechanism for SPF

> The sender domain's public key can be found by including the key ID in
> the SPF record (e.g. "pgp=cc983928"), and this can then be retrieved from
> e.g. pgp.mit.edu. and then cached. Key IDs are supposed to be unique and
...

Keyid's are 4 bytes long, thus there are 4294967295 combinations.
(Same number of potential IP addresses out there, were each IP
addr allowed, no multicast, etc.)

I don't know if a collision has occured yet or not, I'm very
curious.  When verifying a key, you should use both the
keyid, bits, type (DSA/RSA), and fingerprint (fingerprint is
20 bytes long) -- you can eventually forge a specific key id
if you can twiddle the rest.  All together, the work to create
a meaningful key that matches all these characteristics is
either computationally infeasable or impossible, I forget
which...

I wonder how many domains are out there currently - if each
had a key, I'd find it amazing if we didn't have a collision
via the birthday paradox.  1.2*sqrt(4294967295) == 78643 keys,
roughly.

Hmmn - with numbers like that, I'd think we'd already have a collision.
I should go investigate.

(FYI: DSA keyids are simply the last 4 bytes of the fingerprint.)


--
Brian Hatch                  "Was that a compliment?"
   Systems and               "After a fashion."
   Security Engineer         "Then you trust me?"
http://www.ifokr.org/bri/    "After a fashion."

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