This paper revisits double encryption under the lens of multi-user security. We prove that its security degrades only very mildly with an increasing number of users, as opposed to single encryption, where security drops linearly. More concretely, we give a tight bound for the multi-user security of double encryption as a pseudorandom permutation in the ideal-cipher model, and describe matching attacks.
Our contribution is also conceptual: To prove our result, we enhance and generalize the generic technique recently proposed by Hoang and Tessaro for lifting single-user to multi-user security. We believe this technique to be broadly applicable.Category / Keywords: secret-key cryptography / symmetric security, provable security, multi-user security, double encryption Original Publication (with minor differences): IACR-EUROCRYPT-2017 Date: received 15 Feb 2017, last revised 15 Feb 2017 Contact author: hviettung at gmail com Available format(s): PDF | BibTeX Citation Version: 20170220:150126 (All versions of this report) Short URL: ia.cr/2017/145 Discussion forum: Show discussion | Start new discussion