Zcash is the first widespread application of zk-SNARKs, a novel form of zero-knowledge cryptography. The strong privacy guarantee of Zcash is derived from the fact that shielded transactions in Zcash can be fully encrypted on the blockchain, yet still be verified as valid under the network’s consensus rules by using zk-SNARK proofs.page 
YOUTUBE ScY9Z5tZZKU zkSNARKs: what are they? How do their principles apply to security? And more importantly, what is their relationship to cryptocurrency?