Zcash ZEC

A fork of Bitcoin's codebase with zero-knowledge proofs bolted on. A sender can prove to the network that a transfer is valid — the funds exist and are not being spent twice — without revealing addresses or amounts. The cryptography behind this was developed for the purpose and rests on published academic work.

Addresses come in two flavours: transparent ones, as public as Bitcoin's, and shielded ones, where only the existence of an entry is visible. Users choose which to use, and moving between the two types partially discloses the details. Viewing keys exist for reporting: a holder can open their own activity to an auditor or counterparty without opening it to everyone else.

The economics are inherited from Bitcoin: proof of work, a 21 million cap, and a scheduled halving of the block reward. Development is led by a dedicated company that historically received a share of issuance to fund the protocol. The original parameters came out of a closed setup ceremony whose trustworthiness was long criticised, and it was eventually done away with.

Privacy here is optional, and that is its weakness: the smaller the share of shielded transfers, the easier it is to single out whoever uses them.