Ask HN: How can I securely install Truecrypt on OS X?

I want to download an install Truecrypt on OS X 10.9. Unfortunately, the Mac installer available on the Truecrypt website is not signed the way that OS X installers are normally signed. Instead, I need to use the PGP method described on this page: http://www.truecrypt.org/docs/digital-signatures So the problem then becomes: How can I securely install a program to check PGP signatures? I've come across 3 options, each with problems: 1. Download the GnuPG source zip file and check the SHA-1 checksum as described here: http://www.gnupg.org/download/index.html But isn't it possible for a 'man in the middle' to tamper with the download while still producing the same SHA-1 checksum? 2. Download the Mac installer from this site: http://gpgtools.org/ But it is signed by someone called 'Lukas Pitschl' who I've never heard of and so cannot trust. 3. Download the Macports installer and install GnuPG as described here: http://www.mattnworb.com/post/16019918033/how-to-verify-a-pgp-signature-with-gnupg But the Macports OS X installer is signed by Robert Mercer - again, this is someone I have never heard of and cannot trust. So how can I install Truecrypt securely without trusting someone I've never heard of?