Subversion-Resistant Commitment Schemes: Definitions and Constructions

Karim Baghery

Paper 2019/1065

Subversion-Resistant Commitment Schemes: Definitions and Constructions

Karim Baghery

Abstract

A commitment scheme allows a committer to create a commitment to a secret value, and later may open and reveal the secret value in a verifiable manner. In the common reference string model, (equivocal) commitment schemes require a setup phase which is supposed to be done by a third trusted party. Recently, various news is reported about the subversion of $\textit{trusted}$ setup phase in mass-surveillance activities; strictly speaking about commitment schemes, recently it was discovered that the SwissPost-Scytl mix-net uses a trapdoor commitment scheme, that allows undetectably altering the votes and breaking users' privacy, given the trapdoor [Hae19, LPT19]. Motivated by such news and recent studies on subversion-resistance of various cryptographic primitives, this research studies the security of commitment schemes in the presence of a maliciously chosen commitment key. To attain a clear understanding of achievable security, we define a variety of current definitions called subversion hiding, subversion equivocality, and subversion binding. Then we provide both negative and positive results on constructing subversion-resistant commitment schemes, by showing that some combinations of notions are not compatible while presenting subversion-resistant constructions that can achieve other combinations.

Note: This is the full version of the paper published in Security and Trust Management 2020.

Metadata

Available format(s): PDF
Category: Foundations
Publication info: Published elsewhere. Minor revision. The 16th International Workshop on Security and Trust Management
Keywords: Commitment schemes subversion security reducing trust CRS model
Contact author(s): karim baghery @ ut ee
baghery karim @ gmail com
History: 2020-08-17: revised; 2019-09-21: received; See all versions
Short URL: https://ia.cr/2019/1065
License: CC BY

BibTeX

@misc{cryptoeprint:2019/1065,
      author = {Karim Baghery},
      title = {Subversion-Resistant Commitment Schemes: Definitions and Constructions},
      howpublished = {Cryptology ePrint Archive, Paper 2019/1065},
      year = {2019},
      note = {\url{https://eprint.iacr.org/2019/1065}},
      url = {https://eprint.iacr.org/2019/1065}
}