SAT-Based Public Key Cryptosystem I am researching post quantum cryptography and I've stumbled upon this article which presents a PKC with an np-complete (SAT) trapdoor.

I was wondering if someone could help me understand the way the encryption works. From what I understand the cipher text is a formula which consist of a bit (the message) which is then xored with variables taken from the public key. Doesn't it mean that the bit is actually in "plain sight" inside the cipher text ? 

Surely I am missing something.
There are known impossibility results regarding basis public-key cryptography on NP-complete problems. In this paper by Goldreich and Goldwasser they show that under common types of reductions, it is not possible to base public-key cryptography on NP-hardness.