• Traditional hash functions (SHA-256, etc.) are fast for regular computations but require many bitwise operations, making them inefficient for ZK circuits.
• ZK-friendly hash functions are designed for ZK proofs and operate over finite fields used in ZK-proof systems. This allows for efficient proof generation.

Three Classes of ZK-Friendly Hash Functions

1. Low-degree round functions (e.g., MiMC, Poseidon):

   • Use simple operations in each round but require many rounds for security.
   • Offer a good balance between security and efficiency within ZK circuits.

2. Low-degree equivalence (e.g., Rescue, Griffin):

   • Achieve better efficiency within ZK circuits by proving an equivalent but lower-degree constraint.
   • Slower for regular computations outside ZK circuits.

3. Lookup-based round functions (e.g., Monolith):

   • Utilize lookup tables for faster computations within ZK circuits (if supported by the proof system).
   • Offer close to regular hash function speeds for computations outside ZK circuits.