### On QA-NIZK in the BPK Model

Behzad Abdolmaleki, Helger Lipmaa, Janno Siim, and Michał Zając

##### Abstract

Recently, Bellare et al. defined subversion-resistance (security in the case the CRS creator may be malicious) for NIZK. In particular, a Sub-ZK NIZK is zero-knowledge, even in the case of subverted CRS. We study Sub-ZK QA-NIZKs, where the CRS can depend on the language parameter. First, we observe that subversion zero-knowledge (Sub-ZK) in the CRS model corresponds to no-auxiliary-string non-black-box NIZK in the Bare Public Key model, and hence, the use of non-black-box techniques is needed to obtain Sub-ZK. Second, we give a precise definition of Sub-ZK QA-NIZKs that are (knowledge-)sound if the language parameter but not the CRS is subverted and zero-knowledge even if both are subverted. Third, we prove that the most efficient known QA-NIZK for linear subspaces by Kiltz and Wee is Sub-ZK under a new knowledge assumption that by itself is secure in (a weaker version of) the algebraic group model. Depending on the parameter setting, it is (knowledge-)sound under different non-falsifiable assumptions, some of which do not belong to the family of knowledge assumptions.

Note: 14 Feb 2020: this eprint corresponds to the version accepted to PKC 2020. It is very different from the older eprint: we now achieve security also in the case the language parameter is subverted ("Sub-PAR soundness/knowledge-soundness"), we additionally prove knowledge-soundness in the case the language-parameter matrix is full-rank. We also use somewhat different assumptions: in particular, Sub-PAR (knowledge-)soundness relies on interactive non-falsifiable assumptions, that are markedly different from knowledge assumptions that are used in the case of SNARKs. 19 Feb 2019: This version is substantially updated: the main new protocol is better explained (and the case k = 2 is simplified), the security proof is different, etc.17 May 2019: This version has a bit more common terminology. Somewhat better comparison with the previous work.

Available format(s)
Category
Cryptographic protocols
Publication info
Keywords
Bare public key modelno-auxiliary-string zero knowledgenon-black-box zero knowledgeQA-NIZKsubversion-security
Contact author(s)
helger lipmaa @ gmail com
History
2020-02-14: last of 3 revisions
See all versions
Short URL
https://ia.cr/2018/877

CC BY

BibTeX

@misc{cryptoeprint:2018/877,
author = {Behzad Abdolmaleki and Helger Lipmaa and Janno Siim and Michał Zając},
title = {On QA-NIZK in the BPK Model},
howpublished = {Cryptology ePrint Archive, Paper 2018/877},
year = {2018},
note = {\url{https://eprint.iacr.org/2018/877}},
url = {https://eprint.iacr.org/2018/877}
}

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