subpacket of type 20 has critical bit set

[David Shaw]

On Wed, Aug 22, 2007 at 08:40:25AM -0400, Kevin Coates wrote:
> 
> Occasionally the console session will display "subpacket of type 20 has
> critical bit set" when verifying certain signatures. What exactly is
> this message telling me and is it of any concern to me or the key owner?

It means that the person who made that signature set a notation on it,
and marked that notation as "critical".  That means, essentially, "if
you don't understand this notation, you cannot understand this
signature".  Thus, that signature is not usable.

The only notations that GPG understands, and thus allows to be
critical without invalidating the signature are:

  preferred-email-encoding at pgp.com
and
  pka-address at gnupg.org

Note that the critical notation might be set on a key or data
signature.  That message can be from either.

David