Paper 2025/1127 Original: eprint.iacr.org/2025/1127 ↗

KIVR: Committing Authenticated Encryption Using Redundancy and Application to GCM, CCM, and More

Abstract

Constructing a committing authenticated encryption (AE) satisfying the CMT-4 security notion is an ongoing research challenge. We propose a new mode KIVR, a black-box conversion for adding the CMT-4 security to existing AEs. KIVR is a generalization of the Hash- then-Enc (HtE) [Bellare and Hoang, EUROCRYPT 2022] and uses a collision-resistant hash function to generate an initial value (or nonce) and a mask for redundant bits, in addition to a temporary key. We ob- tain a general bound r/2 + tag-col with r-bit redundancy for a large class of CTR-based AEs, where tag-col is the security against tag-collision at- tacks. Unlike HtE, the security of KIVR linearly increases with r, achiev- ing beyond-birthday-bound security. With a t-bit tag, tag-col lies 0 ≤ tag-col ≤ t/2 depending on the target AE. We set tag-col = 0 for GCM, GCM-SIV, and CCM, and the corresponding bound r/2 is tight for GCM and GCM-SIV. With CTR-HMAC, tag-col = t/2, and the bound (r + t)/2 is tight.