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Tjaden Hess

4 posts

A deep dive into Axiom’s Halo2 circuits

Over two audits in 2023, we reviewed a blockchain system developed by Axiom that allows computing over the entire history of Ethereum, all verified by zero-knowledge proofs (ZKPs) on-chain using ZK-verified elliptic curve and SNARK recursion operations. This system is built using the Halo2 framework—a complex, emerging technology that presents many challenges when building a secure application, including potential under-constrained issues resulting from its low-level API.

We wrote the code, and the code won

Earlier this week, NIST officially announced three standards specifying FIPS-approved algorithms for post-quantum cryptography. The Stateless Hash-Based Digital Signature Algorithm (SLH-DSA) is one of these standardized algorithms. The Trail of Bits cryptography team has been anticipating this announcement, and we are excited to share an announcement of our own: we built an open-source pure-Rust implementation of SLH-DSA, which has been merged into RustCrypto.

Tag, you’re it: Signal tagging in Circom

We at Trail of Bits perform security reviews for a seemingly endless stream of applications that use zero-knowledge (ZK) proofs. While fast new arithmetization and folding libraries like Halo2, Plonky2, and Boojum are rapidly gaining adoption, Circom remains a mainstay of ZK circuit design. We’ve written about Circom safety before in the […]