Zcash is a decentralized and open-source cryptocurrency that offers privacy and selective transparency of transactions. Zcash payments are published on a public blockchain, but the sender, recipient, and amount of a transaction remain private.
Zcash is based on peer-reviewed cryptographic research, and built by a security-specialized engineering team on an open source platform based on Bitcoin Core's battle-tested codebase. Major improvement over Bitcoin is the addition of privacy. Zcash uses advanced cryptographic techniques, namely zero-knowledge proofs, to guarantee the validity of transactions without revealing additional information about them.
Zcash encrypts the contents of shielded transactions. Since the payment information is encrypted, the protocol uses a novel cryptographic method to verify their validity.
Zcash uses a zero-knowledge proof construction called a zk-SNARK, developed by team of experienced cryptographers based on recent breakthroughs in cryptography. These constructions allow the network to maintain a secure ledger of balances without disclosing the parties or amounts involved. Instead of publicly demonstrating spend-authority and transaction values, the transaction metadata is encrypted and zk-SNARKs are used to prove that nobody is cheating or stealing.
Zcash also enables users to send public payments which work similarly to Bitcoin. With the support for both shielded and transparent addresses, users can choose to send Zcash privately or publicly. Zcash payments sent from a shielded address to a transparent address reveal the received balance, while payments from a transparent address to a shielded address protect the receiving value.
The acronym zk-SNARK stands for “Zero-Knowledge Succinct Non-Interactive Argument of Knowledge,” and refers to a proof construction where one can prove possession of certain information, e.g. a secret key, without revealing that information, and without any interaction between the prover and verifier.
“Zero-knowledge” proofs allow one party (the prover) to prove to another (the verifier) that a statement is true, without revealing any information beyond the validity of the statement itself. For example, given the hash of a random number, the prover could convince the verifier that there indeed exists a number with this hash value, without revealing what it is.
In a zero-knowledge "Proof of Knowledge" the prover can convince the verifier not only that the number exists, but that they in fact know such a number - again, without revealing any information about the number.Succinct” zero-knowledge proofs can be verified within a few milliseconds, with a proof length of only a few hundred bytes even for statements about programs that are very large. In the first zero-knowledge protocols, the prover and verifier had to communicate back and forth for multiple rounds, but in “non-interactive” constructions, the proof consists of a single message sent from prover to verifier. Currently, the only known way to produce zero-knowledge proofs that are non-interactive and short enough to publish to a block chain is to have an initial setup phase that generates a common reference string shared between prover and verifier.
