Zcash

Zcash brought zero-knowledge proofs into production cryptocurrency, letting a transaction be verified as valid without revealing sender, receiver or amount. Privacy is optional: addresses can be transparent or shielded, and that choice is both its main flexibility and its central weakness.

zk-SNARKs proved a difficult thing possible

A shielded transaction proves that inputs equal outputs and that the spender was authorised, while revealing none of the values or parties. Zcash was the first production deployment of this at scale, and the cryptography it pioneered now underpins a large part of the blockchain scaling industry — an influence far beyond the coin itself.

Optional shielding weakens the anonymity set

If most transactions are transparent, the minority using shielded addresses are visibly doing so, and the pool they hide within is small. This is the standing technical criticism of Zcash relative to mandatory-privacy designs, and it is a matter of usage patterns rather than of cryptographic strength.

The trusted setup, and moving past it

Early shielded transactions relied on parameters generated in a ceremony whose secret material, if retained, would have allowed undetectable counterfeiting. Multi-party ceremonies were designed so that a single honest participant destroying their share made this impossible. Later protocol upgrades removed the requirement for new setups entirely.

Bitcoin's monetary schedule, different mechanics

Zcash retains a 21 million cap and a halving structure. Early issuance included a founders' allocation, later restructured into a development fund — a governance and funding history worth reading, since it differs materially from Bitcoin's.

Where it sits

Zcash offers the strongest privacy cryptography with weaker practical privacy than a mandatory system, and a research programme that has influenced the entire field. Users wanting privacy must actually use shielded addresses, and most historically have not.