Blockchains are often associated with transparency and the public availability of information. However, there are certain use cases where this level of transparency is more desirable and necessary. This is where zero-knowledge proofs (ZKPs) come into play.
ZKPs are a type of cryptographic proof that allows one party (the prover) to prove to another party (the verifier) that they possess certain information without revealing the actual information itself. This allows for privacy and confidentiality to be maintained while still being able to prove that something is true.
One of the key benefits of ZKPs is their ability to enable confidential transactions on a public blockchain. This can be particularly useful when transmitted information is sensitive or personal, such as medical records or financial data.
ZKPs can also enhance the security of a blockchain by allowing for verifiable, trustless authentication of transactions. This can help to prevent fraud and ensure the integrity of the blockchain.
In addition, ZKPs has the potential to enable scalability improvements in blockchains. By allowing for the verification of transactions without revealing all of the underlying data, ZKPs can reduce the amount of data that needs to be stored on the blockchain, making it more efficient and scalable.
Zero-knowledge-proof systems can be broadly classified into interactive and non-interactive.
Interactive zero-knowledge proofs, also known as zero-knowledge interactive proof systems (ZKIPs), involve a back-and-forth communication between a prover and a verifier. The prover tries to convince the verifier that a statement is true without revealing additional information.
One of the earliest examples of an interactive zero-knowledge proof is the Feige-Fiat-Shamir (FFS) protocol. In this protocol, the prover sends a random challenge to the verifier, and the verifier responds with a response. The prover then sends proof that the challenge and response are correctly correlated.
Non-interactive zero-knowledge proof systems, also known as zero-knowledge Succinct Non-Interactive Arguments of Knowledge (zk-SNARKs), involve a single message from the prover to the verifier. The prover creates a proof consisting of a public and a private component and sends the public component to the verifier. The verifier can then use the public component to verify the proof without additional communication.
One of the most well-known examples of a non-interactive zero-knowledge proof system is zk-SNARK, which stands for "Zero-Knowledge Succinct Non-Interactive Argument of Knowledge." zk-SNARKs have been used in many blockchain projects, including Zcash and Ethereum.
Both interactive and non-interactive zero-knowledge-proof systems have their benefits and trade-offs. Interactive proof systems are generally faster and simpler to implement but require back-and-forth communication between the prover and verifier. Non-interactive proof systems are usually more efficient but more complex to implement and need a trusted setup.
There are several different types of ZKP systems, each with unique characteristics and applications.