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Enhancing Security with Built-in Tamper Resilience in Cryptographic Tokens

This paper explores the concept of Built-in Tamper Resilience (BiTR) for cryptographic tokens, addressing the vulnerabilities of traditional cryptography where adversaries can access or tamper with internal states. It proposes modeling tamper-resistant tokens within a universal composability framework and introduces the new functionality of BiTR tokens, demonstrating that they can withstand affine tampering. The protocol ensures that tampering provides no advantage to the adversary, paving the way for secure operations even in compromised environments.

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Enhancing Security with Built-in Tamper Resilience in Cryptographic Tokens

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  1. BiTR: Built-in Tamper Resilience Seung Geol Choi (U. Maryland) Joint work with Aggelos Kiayias (U. Connecticut) Tal Malkin (Columbia U.)

  2. Motivation • Traditional cryptography • internal state: inaccessible to the adversary. • In reality • Adv may access/affect the internal state • E.g., leaking, tampering • Solution? • Make better hardware • Or, make better cryptography

  3. In this work • Focus on tampering hardware tokens • In the universal composability framework

  4. Modeling Tamper-Resilient Tokensin UC

  5. Tamper-Proof Tokens [Katz07] • Ideal functionality Create ! Forge Run …. Run

  6. Tamperable Tokens • Introduce new functionality Create ! Forge Run Tamper

  7. Built-in Tamper Resilience (BiTR) • M is -BiTR • In any environment w/ M deployed as a token, tampering gives no advantage: s.t. indistinguishable

  8. Questions • Are there BiTR tokens? • Yes, with affine tamperings. • UC computation from tamperable tokens? • Generic UC computation from tamper-proof tokens [Katz07] • Yes, with affine tamperings.

  9. Affine Tampering • Adversary can apply an affine transformation on private data.

  10. Schnorr Identification

  11. Schnorr-token is affine BiTR

  12. UC-secure Computation with Tamperable Tokens

  13. Commitment Functionality • Complete for general UC computation. m ! open m

  14. DPG-commitment • DPG: dual-mode parameter generation using hardware tokens • Normal mode • Parameter is unconditionally hiding • Extraction mode • The scheme becomes extractable commitment.

  15. DPG-Commitment from DDH • Parameter: • Com(b) = • Extraction Mode • DH tuple with • Trapdoor r allows extraction • Normal Mode • Random tuple • Com is unconditionally hiding.

  16. Realizing Fmcom from tokens • DPG-Parameter: (pS, pR) • S obtains pR, by running R’s token. • R obtains pS, by running S’s token. • exchange pS and pR • Commit: (Com(m), dpgCompS(m), π) • π: WI (same msg) or (pR from ext mode) • Reveal: (m, π‘) • π': WI (Com(m)) or (pR: ext mode)

  17. UC-security of the scheme • The scheme • Commit: (Com(m), dpgCompS(m), π) • π: WI (same msg) or (pR from ext mode) • Reveal: (m, π‘) • π': WI (Com(m)) or (pR: ext mode) • S*: Make the pS extractable and extract m. • R*: Make the pR extractable and equivocate.

  18. DPG from tamperable tokens • [Katz07] showed DPG-commitment • Unfortunately, the token description is not BiTR. • Our approach: Modify Katz’s scheme to be BiTR.

  19. BiTR DPG

  20. BiTR DPG • The protocol is affine BiTR • Similar to the case of Schnorr • Compose with a BiTR signature • Okamato signature [Oka06] • In this case, the composition works.

  21. Summary • BiTR security • Affine BiTR protocols • UC computation from tokens tamperable w/ affine functions • In the paper • Composition of BiTR tokens • BiTR from deterministic non-malleable codes

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