[codethief]

> IE you can take a secret key system, hardwire the key into the program, and turn it into a public key system without fear that the secret key will be recovered - instead, it will not be distinguishable from other programs with different hardwired keys.

I don't understand. Shouldn't a different secret key yield a different function / circuit?

[DannyBee]

You can actually do it both ways - where the ciphertext is an obfuscated program, and where keys a programs and ciphertexts are short.

https://eprint.iacr.org/2013/454.pdf and friends have a direct description of the latter and references to the former.

This is just one mechanism.