Formal Verification of Permission Voucher

TL;DR

The paper tackles the challenge of formally verifying the Permission Voucher Protocol in distributed access-control settings. It adopts the Tamarin Prover, a symbolic, multisets-rewriting based verifier, to model trust relationships, channels, and adversary capabilities under the Dolev-Yao framework, and to prove a set of security lemmas (including voucher authenticity, data confidentiality, and mutual authentication) while illustrating how dependency graphs support reasoning about proofs. Key contributions include a detailed Tamarin model of the protocol, explicit lemmas with verified outcomes (and traces when attacks are found), demonstrated replay-attack demonstrations with nonce-based protections, and a discussion of practical enhancements such as timestamp-based validity and stronger insider-threat considerations. The work highlights both the strengths of Tamarin in handling complex security properties and its limitations in scalability and in capturing certain real-world threat models, offering strategies to mitigate these issues for large-scale deployments.

Abstract

Formal verification is a critical process in ensuring the security and correctness of cryptographic protocols, particularly in high-assurance domains. This paper presents a comprehensive formal analysis of the Permission Voucher Protocol, a system designed for secure and authenticated access control in distributed environments. The analysis employs the Tamarin Prover, a state-of-the-art tool for symbolic verification, to evaluate key security properties such as authentication, confidentiality, integrity, mutual authentication, and replay prevention. We model the protocol's components, including trust relationships, secure channels, and adversary capabilities under the Dolev-Yao model. Verification results confirm the protocol's robustness against common attacks such as message tampering, impersonation, and replay. Additionally, dependency graphs and detailed proofs demonstrate the successful enforcement of security properties like voucher authenticity, data confidentiality, and key integrity. The study identifies potential enhancements, such as incorporating timestamp-based validity checks and augmenting mutual authentication mechanisms to address insider threats and key management challenges. This work highlights the advantages and limitations of using the Tamarin Prover for formal security verification and proposes strategies to mitigate scalability and performance constraints in complex systems.

Figures (10)

• Figure 1: Tamarin dependency graph when IDApp creates PermissionVoucher
• Figure 2: Tamarin dependency graph when OWNER unlocks IDCard
• Figure 3: Tamarin dependency graph when OWNER connects to OnPremise Service
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Theorems & Definitions (8)

• Lemma : Replay Possible
• Lemma : Authentication: Ensure that only a valid ID-CARD can be unlocked by a correct PIN
• Lemma : Voucher Authenticity: Ensure that only the ID APP can create a valid permission voucher
• Lemma : Voucher Integrity: Ensure that a permission voucher is not modified during transfer
• Lemma : No Replay Nonce: Ensure that each nonce used during the process is unique and prevents replay attacks
• Lemma : Visitor Pass Authenticity: Ensure that a visitor pass can only be generated by the ID-VERIFIER after a valid voucher is redeemed
• Lemma : Data Items Confidentiality: Ensure that selected data items remain confidential unless explicitly shared by the OWNER
• Lemma : Mutual Authentication