Intermediary Audit Report

29/10/2025

Properly formatted code can be seen in the web version of this report: Web Version Link

Background

Solana's Token-2022 Program via the Confidential Transfer extension enables users to transact with encrypted balance amounts while maintaining blockchain transactions verifiability through the use of appropriate cryptographic schemes. Concretely, the confidential transfer extension uses a variant of the ElGamal encryption (i.e., twisted ElGamal encryption), sigma protocols and Bulletproof-based range proofs to prove transaction validity without revealing actual amounts.

Overall Audit Objectives

The primary objectives of the overall audit are to:

• Review the associated documentation provided by the client
• Audit the zk ElGamal proof program
• Audit the implementation of the sigma proofs for completeness, computational knowledge soundness and for the zero-knowledge properties
• Audit the implementation of various range proofs for soundness
• Audit the implementation of the twisted ElGamal encryption scheme and its integration with various proof systems
• Review the design and audit the implementation of the Confidential Transfer algorithm(s) and components
• Test edge cases and potential security bypass scenarios
• Provide recommendations for additional security hardening

The Scope of the Intermediary Report

The audit’s top priority is the verification path of the CT protocol and the verification path in zk-elgamal-proof repository.