[hurin]

I too can post a public key I have the private key for and a factor? Or intentionally create a weak key?

[schoen]

Yes you can, we just need to find hpa's n value and see whether it is divisible by 231. If it is, the claim is correct.

I found the n value for my own PGP public key before and I can find hpa's too, I just have to remember the right arguments to gpg.

[cjbprime]

It's: gpg --list-key --with-key-data <id>

[cnvogel]

    $ gpg --export -a $$KEYID$$ >keyfile.asc   
    $ gpg --list-packets --debug=0x02 keyfile.asc

...but I don't know if the pkey[] values are directly usable, or have some substructure.

[davout]

you can trivially verify a key was broken if it was, duh, broken