Paper 2019/1120

Structure-Preserving Signatures on Equivalence Classes From Standard Assumptions

Mojtaba Khalili, Daniel Slamanig, and Mohammad Dakhilalian


Structure-preserving signatures on equivalence classes (SPS-EQ) introduced at ASIACRYPT 2014 are a variant of SPS where a message is considered as a projective equivalence class, and a new representative of the same class can be obtained by multiplying a vector by a scalar. Given a message and corresponding signature, anyone can produce an updated and randomized signature on an arbitrary representative from the same equivalence class. SPS-EQ have proven to be a very versatile building block for many cryptographic applications. In this paper, we present the first EUF-CMA secure SPS-EQ scheme under standard assumptions. So far only constructions in the generic group model are known. One recent candidate under standard assumptions are the weakly secure equivalence class signatures by Fuchsbauer and Gay (PKC'18), a variant of SPS-EQ satisfying only a weaker unforgeability and adaption notion. Fuchsbauer and Gay show that this weaker unforgeability notion is sufficient for many known applications of SPS-EQ. Unfortunately, the weaker adaption notion is only proper for a semi-honest (passive) model and as we show in this paper, makes their scheme unusable in the current models for almost all of their advertised applications of SPS-EQ from the literature. We then present a new EUF-CMA secure SPS-EQ scheme with a tight security reduction under the SXDH assumption providing the notion of perfect adaption (under malicious keys). To achieve the strongest notion of perfect adaption under malicious keys, we require a common reference string (CRS), which seems inherent for constructions under standard assumptions. However, for most known applications of SPS-EQ we do not require a trusted CRS (as the CRS can be generated by the signer during key generation). Technically, our construction is inspired by a recent work of Gay et al. (EUROCRYPT'18), who construct a tightly secure message authentication code and translate it to an SPS scheme adapting techniques due to Bellare and Goldwasser (CRYPTO'89).

Available format(s)
Public-key cryptography
Publication info
A major revision of an IACR publication in ASIACRYPT 2019
SignaturesStandard AssumptionsTight Security
Contact author(s)
m khalili @ ec iut ac ir
daniel slamanig @ ait ac at
2019-10-01: received
Short URL
Creative Commons Attribution


      author = {Mojtaba Khalili and Daniel Slamanig and Mohammad Dakhilalian},
      title = {Structure-Preserving Signatures on Equivalence Classes From Standard Assumptions},
      howpublished = {Cryptology ePrint Archive, Paper 2019/1120},
      year = {2019},
      note = {\url{}},
      url = {}
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