International Association
for Cryptologic Research

In this note, we identify a minor flaw in the design of the XOCB mode, presented at Eurocrypt '23. This vulnerability enables trivial tag forgeries and arises from the padding applied to messages. We examine the security proof and pinpoint the presence of the flaw within it. Furthermore, we propose a simple fix for this issue, drawing upon the features of OCB3, and discuss the implications of this modification on the proof of security.