The technical conditions are a bit more specific (that an attacker can't distinguish between the encryptions of two functionally equivalent programs), but the study of indistinguishability obfuscation (abbreviated iO), has been called a "watershed" in cryptography.
I have pointed many friends--technical and non-technical alike--to Moxie's talk because in addition to some basics of how crypto works, it helps people understand why cryptography is essential to open societies in historical context. The linked essay points out some important basics, but it doesn't really explain why things like the deniability properties of OTR, trust agility for CAs, or perfect forward secrecy are so vital in today's world.
* One Time Pad (OTP)
* symmetric ciphers
* asymmetric cryptography (minus signatures)
* homomorphic encryption (at least, the overall principle)
* side-channels attack
Giving more practical examples could have helped though (e.g. HTTPS, GPG, etc)