TOPPSS: Cost-Minimal Password-Protected Secret Sharing Based on Threshold OPRF

Stanisław Jarecki, Aggelos Kiayias, Hugo Krawczyk, Jiayu Xu

Research output: Chapter in Book/Report/Conference proceedingConference contribution


We present TOPPSS, the most efficient Password-Protected Secret Sharing (PPSS) scheme to date. A (t, n)-threshold PPSS, introduced by Bagherzandi et al. [4], allows a user to share a secret among n servers so that the secret can later be reconstructed by the user from any subset of t+1t+1 servers with the sole knowledge of a password. It is guaranteed that any coalition of up to t corrupt servers learns nothing about the secret (or the password). In addition to providing strong protection to secrets stored online, PPSS schemes give rise to efficient Threshold PAKE (T-PAKE) protocols that armor single-server password authentication against the inherent vulnerability to offline dictionary attacks in case of server compromise.

TOPPSS is password-only, i.e. it does not rely on public keys in reconstruction, and enjoys remarkable efficiency: A single communication round, a single exponentiation per server and just two exponentiations per client regardless of the number of servers. TOPPSS satisfies threshold security under the (Gap) One-More Diffie-Hellman (OMDH) assumption in the random-oracle model as in prior efficient realizations of PPSS/T-PAKE [18, 19]. Moreover, we show that TOPPSS realizes the Universally Composable PPSS notion of [19] under a generalization of OMDH, the Threshold One-More Diffie-Hellman (T-OMDH) assumption. We show that the T-OMDH and OMDH assumptions are both hard in the generic group model.

The key technical tool we introduce is a universally composable Threshold Oblivious PRF which is of independent interest and applicability.
Original languageEnglish
Title of host publicationApplied Cryptography and Network Security
Subtitle of host publication15th International Conference, ACNS 2017, Kanazawa, Japan, July 10-12, 2017, Proceedings
EditorsDieter Gollmann, Atsuko Miyaji, Hiroaki Kikuchi
Place of PublicationCham
PublisherSpringer, Cham
Number of pages20
ISBN (Electronic)978-3-319-61204-1
ISBN (Print)978-3-319-61203-4
Publication statusPublished - 26 Jun 2017
Event15th International Conference on Applied Cryptography and Network Security - Kanazawa, Japan
Duration: 10 Jul 201712 Jul 2017

Publication series

NameLecture Notes in Computer Science
Publisher Springer, Cham
ISSN (Print)0302-9743


Conference15th International Conference on Applied Cryptography and Network Security
Abbreviated titleACNS 2017
Internet address


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