ZKP学习笔记

ZK-Learning MOOC课程笔记

Lecture 6: Discrete-log-based Polynomial Commitments (Yupeng Zhang)

6.3 Bulletproofs and other schemes based on discrete-log

• KZG:

  • Pros:
    • Commitment and proof size: O(1), 1 group element
    • Verifier time: O(1) pairing
  • Cons: trusted setup

• Bulletproofs [BCCGP’16, BBBPWM’18]

• Transparent setup: sample random $g_0,g_1,g_2,...,g_d$ in $G$
  

• High-level idea

  • Example: 3-degree polynomial
    

  • Degree reduction: 3 degree -> 1 degree -> constant degree
    

  • Cross term to commit L and R

  • Similar with FFT

• Correctness
  

• Eval and Verify
  

• Properties of Bulletproofs

  • Keygen: O(d), transparent setup!
  • Commit: O(d) group exponentiations, O(1) commitment size
  • Eval: O(d) group exponentiations (non-interactive via Fiat Shamir)
  • Proof size: O(log d)
  • Verifier time: O(d)

• Other improvement

  • Hyrax [Wahby-Tzialla-shelat-Thaler-Walfish’18]
    • Improves the verifier time to O(d) by representing the coefficients as a 2-D matrix
    • Proof size: O($\sqrt{d}$)
  • Dory [Lee’2021]
    • Base on pairing
    • Improving verifier time to O(log d)
    • Key idea: delegating the structured verifier computation to the prover using inner pairing product arguments [BMMTV’2021]
    • Also improves the prover time to O($\sqrt{d}$)exponentiations plus O(d) field operations
  • Dark [Bünz-Fisch-Szepieniec’20]
    • Based on group of unknown order
    • Achieves O(log d) proof size and verifier time
      • Delegate some part of verifier to the prover

• Summary