A16z Crypto updates Jolt zkVM, challenges loose use of ‘ZK’ label

A16z Crypto, the web3 arm of the major venture capital firm Andreessen Horowitz, took aim at the colloquial use of “ZK” in some developer setups in a recent blog post about its Jolt zkVM. 

“Most zkVMs are not actually zero knowledge — unless an expensive ‘wrapping’ procedure is applied,” the blog reads. “This wrapping typically involves recursively proving the verification of the zkVM proof inside another proof system that

The authors also noted that often “zk” has become a kind of shorthand for “the property of succinctness,” meaning proofs that are “short and fast to verify,” rather than true zero-knowledge privacy. 

“As the community’s focus on privacy grows — requiring true zero knowledge, which is about privacy of the prover’s sensitive data — this misuse of terminology is becoming a real problem,” a16z added. 

What are ZK proofs?

ZK proofs are a cryptographic technique that lets one party (the prover) convince another party (the verifier) that a statement is true without revealing any underlying information beyond the fact that the statement is true.

First developed within academia, the first large-scale commercial application of ZK proofs arguably took root within the crypto industry, particularly with the launch of Zcash, which deployed a type of succinct proof called zk-SNARKs to provide onchain privacy by shielding transaction data.  

However, zero-knowledge cryptography has since been applied in several novel blockchain use cases, particularly as a scaling solution for Ethereum Layer 2 blockchains and other zk-Rollups. 

Privacy itself has reemerged as an important concern among crypto developers and investors, who argue that the transparent nature of most blockchains today will limit adoption, particularly among institutions.

Digital Currency Group CEO Barry Silbert, for instance, recently said he expects significant financial flows into privacy chains. 

Jolt's solution

For its part, a16z’s open-source Jolt zkVM rolled out a significant new upgrade to natively support zero-knowledge proofs on Tuesday.

So-called Zero-Knowledge Virtual Machines are used to run programs and generate a proof that some code function was executed without revealing their inputs.

Like the applications the blog calls out, Jolt initially used ZK proofs for succinctness rather than full privacy, an issue the developers rectified by turning to a folding scheme that “dates back to the 1990s.”

In particular, Jolt used the NovaBlindFold folding scheme to create blinded proofs to prevent information leakage, “rendering it suitable for privacy applications.”

“The net result is a ZK proof that is only about 3 KB larger than the original non-ZK Jolt proof,” the blog notes.