Correct configuration for atp?

Hi. Apologies in advanced if this is a trivial question which has been documented somewhere. I did not find an answer to it, so here it goes.

What is the right configuration for ‘atp’ on an machine with ia64 debian ports?

When I run ‘atp update’ I get the following error:


Get:1 http://ftp.ports.debian.org/debian-ports sid InRelease [24.2 kB]
Err:1 http://ftp.ports.debian.org/debian-ports sid InRelease
  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 5A88D659DCB811BB
Reading package lists... Done
W: GPG error: http://ftp.ports.debian.org/debian-ports sid InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 5A88D659DCB811BB
E: The repository 'http://ftp.ports.debian.org/debian-ports sid InRelease' is not signed.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.


Thanks.

_____
Pedro