Proof of Knowledge (PoK) Meaning

What is Proof of Knowledge (PoK)?

Cryptographic proofs are validation systems with a prover and a verifier. Proof of knowledge (knowledge proof) in cryptography describes an authentication method in which the prover successfully convinces the verifier that it knows a secret. The prover is an entity with a claim or statement, while the verifier is the one who validates the claim. The prover’s job is to convince the verifier that the statement is true.

Knowledge proofs can either be interactive or non-interactive. In interactive knowledge proofs, the two parties are in direct communication. On the contrary, no direct interaction exists between the participants in non-interactive knowledge proofs.

Other types of cryptographic proofs include zero-knowledge proofs and Zk-SNARKs. 

PoK Explained

Non-interactive knowledge proofs can be used to construct identity verification systems, digital signature schemes, voting systems, and password management. It can also be used in blockchain protocols where transactions need to be validated without revealing the transaction details, such as sender and receiver identities.

Proof of knowledge has two fundamental properties – completeness and soundness.

• Completeness: An honest prover can persuade an honest verifier if their claim that they possess knowledge about something is true. Completeness implies that the statement has to have a high degree of correctness.
• Soundness/validity: A malicious prover cannot persuade an honest verifier if their claim to possess knowledge about something is false.

How is this any different from zero-knowledge proofs (ZKP)? 

A ZKP is an authentication technique involving the two parties, but with the additional “zero-knowledge” aspect. Zero-knowledge implies that the verifier learns nothing from the prover except the truthfulness of the statement.