Cryptology ePrint Archive: Report 2016/564

The Multi-User Security of Authenticated Encryption: AES-GCM in TLS 1.3

Mihir Bellare and Bjoern Tackmann

Abstract: We initiate the study of multi-user (mu) security of authenticated encryption (AE) schemes as a way to rigorously formulate, and answer, questions about the "randomized nonce" mechanism proposed for the use of the AE scheme GCM in TLS 1.3. We (1) Give definitions of mu ind (indistinguishability) and mu kr (key recovery) security for AE (2) Characterize the intent of nonce randomization as being improved mu security as a defense against mass surveillance (3) Cast the method as a (new) AE scheme RGCM (4) Analyze and compare the mu security of both GCM and RGCM in the model where the underlying block cipher is ideal, showing that the mu security of the latter is indeed superior in many practical contexts to that of the former, and (5) Propose an alternative AE scheme XGCM having the same efficiency as RGCM but better mu security and a more simple and modular design.

Category / Keywords: secret-key cryptography / authenticated encryption, TLS 1.3, multi-user security, mass surveillance

Original Publication (with minor differences): IACR-CRYPTO-2016

Date: received 3 Jun 2016, last revised 15 Aug 2016

Contact author: btackmann at eng ucsd edu

Available format(s): PDF | BibTeX Citation

Note: Fixed security proof for RGCM.

Version: 20160815:202002 (All versions of this report)

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