Cryptology ePrint Archive: Report 2015/626

Practical Round-Optimal Blind Signatures in the Standard Model

Georg Fuchsbauer and Christian Hanser and Daniel Slamanig

Abstract: Round-optimal blind signatures are notoriously hard to construct in the standard model, especially in the malicious-signer model, where blindness must hold under adversarially chosen keys. This is substantiated by several impossibility results. The only construction that can be termed theoretically efficient, by Garg and Gupta (Eurocrypt'14), requires complexity leveraging, inducing an exponential security loss.

We present a construction of practically efficient round-optimal blind signatures in the standard model. It is conceptually simple and builds on the recent structure-preserving signatures on equivalence classes (SPS-EQ) from Asiacrypt'14. While the traditional notion of blindness follows from standard assumptions, we prove blindness under adversarially chosen keys under an interactive variant of DDH. However, we neither require non-uniform assumptions nor complexity leveraging.

We then show how to extend our construction to partially blind signatures and to blind signatures on message vectors, which yield a construction of one-show anonymous credentials à la "anonymous credentials light" (CCS'13) in the standard model.

Furthermore, we give the first SPS-EQ construction under non-interactive assumptions and show how SPS-EQ schemes imply conventional structure-preserving signatures, which allows us to apply optimality results for the latter to SPS-EQ.

Category / Keywords: public-key cryptography / (Partially) Blind Signatures, Standard Model, SPS-EQ, One-Show Anonymous Credentials

Original Publication (with major differences): IACR-CRYPTO-2015

Date: received 23 Jun 2015, last revised 26 Jun 2015

Contact author: georg fuchsbauer at ist ac at

Available format(s): PDF | BibTeX Citation

Version: 20150630:184252 (All versions of this report)

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