BAP-674: Privacy-Preserving Token Transfer Protocol

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Summary

BAP-674 specifies a standard interface for privacy-preserving token transfers on BNB Chain, enabling deposit, transfer, and withdraw of BEP-20 tokens (and native BNB) with on-chain confidentiality using a UTXO-based model and zk-SNARK (Groth16) proofs.

Key Features

• Shielded UTXO model: Deposit, transfer, freeze, and withdraw operations with Poseidon2 commitments and nullifiers over BN254
• Amortized Merkle tree: Buffer array (size 32) with frontier-based batch insertion into a depth-32 tree, dual-root verification (merkleRoot + arrayHash)
• Nullifier derivation: Supports both default (direct secret key) and freezer-aware (DH-derived nullifier key) paths
• Compliance layer: Per-pool viewer (ElGamal encryption on BabyJubjub) and freezer (bidirectional freeze/unfreeze toggle) keys
• Relayer model: Per-operation binding input construction preventing parameter tampering, with self-relay support
• Complete event specification: 21 events covering core operations, encrypted data, pool lifecycle, fee claims, and Merkle tree state
• Poseidon2 reference: Full round constants, MDS matrices, and test vectors (Appendix A)

Discussion

https://forum.bnbchain.org/