This code is a smallish change to a largeish program, so of course the original APT authors deserve credit. Also, a similar thing has been implemented by Connectiva in their fork of APT, and we used a small amount of their code.
Having said that, the current version of APT Secure was implemented by Colin Walters and Isaac Jones. Special thanks to Matt Zimmerman who integrated the APT Secure patch into mainline APT, with many changes and improvements.