PGPdump

PGPdump is a PGP packet visualizer by Kazu Yamamoto <kazu@iij.ad.jp>. It supports OpenPGP (RFC 4880) and PGP v2 (RFC 1991) packet formats.

http://www.pgpdump.net/about.html
http://www.mew.org/~kazu/proj/pgpdump/en/
https://github.com/kazu-yamamoto/pgpdump 

brew install pgpdump

Source code: pgpdump-0.35.tar.gz