[Cryptography] Is Non-interactive Zero Knowledge Proof an oxymoron?

[Allen]

> This can be used in the same way as a digital signature...

It would also be correct to say (and this might be what you were  
looking for) that a digital signature algorithm is encompassed by the  
definition I gave for a zero knowledge proof.  In a digital signature  
algorithm, the public inputs are the message hash and the known public  
signing key, and the proof is the signature which proves knowledge of  
a hidden input (the private signing key) without revealing the hidden  
input.  So a digital signature is a non-interactive zero knowledge  
proof of knowledge.  It however does not include a richer set of  
operators that can be used in the conditions or constraint equations  
of other zero knowledge proof systems such as the Zero Knowledge  
Succinct Non-interactive Argument of Knowledge (zk-SNARK) used in the  
CredaCash cryptocurrency.  See [1] and the references cited therein.

[1] CredaCash Transaction Protocol, found at  
https://credacash.com/cryptocurrency/