Or, the easy way is to get a "ppm"ed package from this repository: http://theoryx5.uwinnipeg.ca/ppms/
If you are unable to get to the repository, download & edit the ppd, to find where the corresponding .tar.gz package is, download it and create your own local repository.
Thanks (++) to both of you. Both answers were helpful. I'll look more into J's answer later as its an area I want to learn more about, but at this juncture Olivier's answer gave immediate results. I ppm'd into the your suggested repository and it immediately installed (hassle free!), changed my program to utilise Blowfish and ran the encryption. Perfect! All done in less than a minute.