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BiTR: Built-in Tamper Resilience

BiTR: Built-in Tamper Resilience. Seung Geol Choi (U. Maryland). Joint work with Aggelos Kiayias (U. Connecticut) Tal Malkin (Columbia U.). Motivation. Traditional cryptography internal state: inaccessible to the adversary. In reality Adv may access/affect the internal state

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BiTR: Built-in Tamper Resilience

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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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