Cryptology ePrint Archive: Report 2022/011

Security Analysis of Coconut, an Attribute-Based Credential Scheme with Threshold Issuance

Alfredo Rial and Ania M. Piotrowska

Abstract: Coconut [NDSS 2019] is an attribute-based credential scheme with threshold issuance. We analyze its security properties. To this end, we define an ideal functionality for attribute-based access control with threshold issuance. We describe a construction that realizes our functionality. Our construction follows Coconut with a few changes. In particular, it modifies the protocols for blind issuance of credentials and for credential show so that user privacy holds against computationally unbounded adversaries. The modified protocols are slightly more efficient than those of Coconut. Our construction also extends the public key, which seems necessary to prove unforgeability.

Category / Keywords: cryptographic protocols / Public-key cryptography, digital signatures, zero knowledge

Date: received 4 Jan 2022

Contact author: alfredo at nymtech net

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Version: 20220107:165417 (All versions of this report)

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