tags: Reading sessions

2024

Sphinx-in-the-Head: Group Signatures from Symmetric Primitives

  • LIQUN CHEN, CHANGYU DON, and CHRISTOPHER J. P. NEWTON and YALAN WANG.
  • ACM TOPS 2024
  • [SS] MPC-in-the-Head (MPCitH) is a new paradigm to design signature schemes. Based on this primitive, one builds a Zero Knowledge Proof. Furthermore, that ZKP can be made NIZK, which can be used to construct a signature scheme. PICNIC is an example of a post-quantum signature (submitted to NIST standardization) scheme that has used the MPC-in-the-Head paradigm. This paper has used the MPCitH paradigm to design a group signature. This construction is hash-based, which is a symmetric primitive-based. An essential part of this group signature is group credentials – which is essentially a signature on the user key by the group manager. One of the contributions of this paper is to design such a group credential, which is a variant of the hash-based signature SPHINCS+, which they call F-SPHINCS+. The problem of using SPHINCS+ for this purpose is that it blows up the circuit complexity of the verification algorithm, which they have been able to manage with the variant F-SPHINCS+.The anonymity property of this group signature is achieved through the ZKP approach. When signing a message, the user produces an MPCitH NIZK to show it possesses a group credential, and the signature is generated on the hash of the message (sid) under the keys authorized by the group credential. In SPHINCS+, XMSS signature was used; here in F-SPHINCS, they use M-FORS, which is a new variant of the FORS few-time signature. The novelty that they achieve is less verification time than SPHINCS+.A notable implementation achievement of this group signature is that they can handle a group size as large as 2^60

2023

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2022

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2021

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