There are some public solutions to this problem: http://stackoverflow.com/questions/1882981/google-chrome-alphanumeric-hashes-to-identify-extensions/2050916#2050916

Seems its a hash of the public key, which we have.  Might be a brittle problem which we should bring up on the lists for a more formal answer.  For now, I'de copy some public solution and see if it works, then document it as brittle hack ;)