According to dcSpark co-founder Sebastien Guillemot, the very first ZK (zero-knowledge) smart contract has been deployed on the Cardano mainnet. 

This marks the start of the era of ZK applications on the popular blockchain network. 

The transaction was performed by Cardano developer Input Output with the help of Halo 2 for ZK verification on the blockchain's mainnet. 

As explained by Input Output, the first transaction was meant to lock the funds. The second transaction, which required the verification of the Halo2-generated ZK proof, was performed in order to unlock the funds. 

The unlocking transaction required a 2.03 ADA ($1.9) fee, which is "reasonably low," according to Input Output. 

The Halo 2 zkSNARK proving system, which was created by Zcash creator Electric Coin Company, makes it possible to create and verify cryptographic zk-SNARKs proofs without a need for a trusted setup. 

In a lengthy social media thread, Input Output explained the benefits of the Halo 2 cryptographic technique, which makes it possible to prove that a computation was performed correctly without revealing its details. The Cardano developer specifically mentioned the fact that recursive proofs as one of the most notable features of Halo 2. They make it possible to increase scalability and interoperability by breaking down computations into smaller parts. 

"We still have more work to do. But this test by IO Research represents a significant step forward in the use of zero-knowledge proofs with Cardano, bringing with it a powerful combination of scalability, efficiency, and further enhanced security," Input Output said.