Compactly Committing Authenticated Encryption Using Tweakable Block Cipher

• Published in: Network and System Security Vol. 12570; pp. 187 - 206
• Main Author: Hirose, Shoichi
• Format: Book Chapter
• Language: English
• Published: Switzerland Springer International Publishing AG 2020; Springer International Publishing
• Series: Lecture Notes in Computer Science
• Subjects: Authenticated encryption; Encryptment; Message franking; Tweakable block cipher
• ISBN: 9783030657444; 3030657442
• ISSN: 0302-9743; 1611-3349
• DOI: 10.1007/978-3-030-65745-1_11

Message franking is a cryptographic scheme introduced in the Facebook end-to-end encrypted messaging system. It enables users to report abusive messages to Facebook in a verifiable manner. Grubbs, Lu and Ristenpart initiated theoretical study of message franking. They formalized the notion and introduced a new primitive called compactly committing authenticated encryption with associated data (ccAEAD) in 2017. They also presented provably secure ccAEAD schemes. Dodis, Grubbs, Ristenpart and Woodage introduced a new primitive called encryptment as a core building block of ccAEAD in 2018. They presented a provably secure encryptment scheme using a Merkle-Damgård hash function and transformations to ccAEAD from it. In this paper, we present a provably secure encryptment scheme using a tweakable block cipher (TBC). Then, we present a ccAEAD scheme using a TBC by showing a transformation from encryptment using a TBC. Similar to the previous schemes, our scheme requires a collision-resistant pseudorandom function. We adopt a double-block-length construction using TBC for it.