What is Zcash?
Launching this fall (2016)
Zcash is a decentralized and open-source cryptocurrency that offers privacy and selective transparency of transactions using advanced cryptography. Zcash payments are published on a public blockchain, but the sender, recipient, and amount of a transaction remain private. Zcash software is available in an alpha release for experimentation and software development, but the real currency doesn't yet exist and will not until the official launch this fall. Download the Tech Preview release here, or get started with our Public Alpha Guide.
Transaction metadata
Bitcoin transactions work using triple-entry accounting: transactions combine the "outputs" of previous transactions and split into new outputs of arbitrary value. The spend-authority of the "inputs" of a transaction, as well as the balance of the transaction, are checked manually by all nodes. This means that all unspent outputs must be kept by all fully verifying nodes, but also, that all nodes are aware of all values and parties involved in transactions.
Zero-knowledge proofs
Our zero-knowledge proving scheme makes it possible to hide values and other identifying information from the public. Using advanced cryptographic techniques, users simply prove that the values balance and that they are authorized to spend such value. (And that they have not spent it before.)
Performance
The proofs that we use in our scheme, called zk-SNARKs, are short and take very little time to verify. Transaction "outputs" in our protocol are not retained by full nodes, as they are entered into a finite-size accumulator. Only the spendability of an output is retained. As a result, nearly all components of a transaction can be pruned by fully validating nodes.
Further Information
We're working to provide more in-depth technical specification. You can find further details on our developer wiki's specification page.
https://z.cash