Error when using gpg in a cron job

[Kurt Fitzner]

I have set up an internal machine on my network as a tripwire system 
that checks over my firewall server once each morning and emails me the 
results.  Since my firewall server is also my mail server, I wanted the 
machine sending the mail to sign the email reports - forcing an attacker 
to breach both systems in order to defeat the check.

My problem is when cron runs this command:
   cat /root/.gnupg/pass | $GPG --passphrase-fd 0 --quiet \
     --output $SIGNED --clearsign $REPORT

I get this error:
   gpg: cannot open `/dev/tty': No such device or address

For some reason, gpg is trying to open up a tty directly - for what 
reason, I don't know.

This is running on an HP/UX 11.0 system.  If anyone has any ideas, I'd 
appreciate it.

	Kurt Fitzner