## Cryptology ePrint Archive: Report 2012/537

Intercepting Tokens: The Empire Strikes Back in the Clone Wars

Özgür Dagdelen and Marc Fischlin

Abstract: We discuss interception attacks on cryptographic protocols which rely on trustworthy hardware like one-time memory tokens (Goldwasser et al., Crypto 2008). In such attacks the adversary can mount man-in-the-middle attacks and access, or even substitute, transmitted tokens. We show that many of the existing token-based protocols are vulnerable against this kind of attack, which typically lies outside of the previously considered security models.

We also give a positive result for protocols remaining secure against such attacks. We present a very efficient protocol for password-based authenticated key exchange based on the weak model of one-time memory tokens. Our protocol only requires four moves, very basic operations, and the sender to send  tokens in the first step for passwords of length . At the same time we achieve information-theoretic security in Canetti's universal composition framework (FOCS 2001) against adaptive adversaries (assuming reliable erasure), even if the tokens are not guaranteed to be transferred securely, i.e., even if the adversary can read or substitute transmitted tokens.

Category / Keywords: security model, password based key exchange, information-theoretic, one-time memory tokens

Date: received 11 Sep 2012, last revised 17 Sep 2013

Contact author: oezguer dagdelen at cased de

Available format(s): PDF | BibTeX Citation

Note: Sept. 2013: new results and different focus

Short URL: ia.cr/2012/537

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