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**2020/658**

**Title:**

Time-Specific Signatures

**Authors:**
Masahito Ishizaka, Shinsaku Kiyomoto

**Abstract:**

In Time-Specific Signatures (TSS) parameterized by an integer T\in\mathbb{N}, a signer with a secret-key associated with a numerical value t\in[0,T-1] can anonymously, i.e., without revealing t, sign a message under a numerical range [L,R] such that 0\leq L \leq t\leq R\leq T-1. An application of TSS is anonymous questionnaire, where each user associated with a numerical value such as age, date, salary, geographical position (represented by longitude and latitude) and etc., can anonymously fill in a questionnaire in an efficient manner. In this paper, we propose two \textit{polylogarithmically} efficient TSS constructions based on asymmetric pairing with groups of prime order, which achieve different characteristics in efficiency. In the first one based on a forward-secure signatures scheme concretely obtained from a hierarchical identity-based signatures scheme proposed by Chutterjee and Sarker (IJACT’13), size of the master public-key, size of a secret-key and size of a signature are asymptotically \mathcal{O}(\log T), and size of the master secret-key is \mathcal{O}(1). In the second one based on a wildcarded identity-based ring signatures scheme obtained as an instantiation of an attribute-based signatures scheme proposed by Sakai, Attrapadung and Hanaoka (PKC’16), the sizes are \mathcal{O}(\log T), \mathcal{O}(1), \mathcal{O}(\log^2 T) and \mathcal{O}(\log T), respectively.

**ePrint:**
https://eprint.iacr.org/2020/658

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