GPG error with Debian archives

[Ross Boylan <ross@biostat.ucsf.edu>]

aptitude update gives the errors
W: GPG error: http://http.us.debian.org testing Release: The following
signatures were invalid: BADSIG F1D53D8C4F368D5D Debian Archive
Automatic Signing Key (2005) <ftpmaster@debian.org>
W: GPG error: http://http.us.debian.org unstable Release: The following
signatures were invalid: BADSIG F1D53D8C4F368D5D Debian Archive
Automatic Signing Key (2005) <ftpmaster@debian.org>

apt-key still shows
pub   1024D/4F368D5D 2005-01-31 [expires: 2006-01-31]
uid                  Debian Archive Automatic Signing Key (2005)
<ftpmaster@debian.org>

This just started yesterday; perhaps something magic happened Dec 1?  It
was working before.

I'm surprised there don't seem to be any reports of this; I found some
messages when apt first started using keys, but nothing recent.

I tried apt-key update, but do not have debian-keyring installed.

Before I start randomly installing things (from untrusted archives) I
thought I'd check what's going on.  Does anybody know?

If you could cc this edress I'd appreciate it, as I'm  not subscribed
through it.
-- 
Ross Boylan                                      wk:  (415) 514-8146
185 Berry St #5700                               ross@biostat.ucsf.edu
Dept of Epidemiology and Biostatistics           fax: (415) 514-8150
University of California, San Francisco
San Francisco, CA 94107-1739                     hm:  (415) 550-1062