Breaking Enhanced CBC and Its Application

Shuping Mao, Peng Wang, Yan Jia, Gang Liu () and Ying Chen
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Shuping Mao: Department of Cryptology Science and Technology, Beijing Electronic Science and Technology Institute, Beijing 100070, China
Peng Wang: School of Cryptology, University of Chinese Academy of Sciences, Beijing 100049, China
Yan Jia: State Key Laboratory of Cyberspace Security Defense, Institute of Information Engineering, Chinese Academy of Sciences, Beijing 100085, China
Gang Liu: National Key Laboratory of Security Communication, Chengdu 610041, China
Ying Chen: Department of Cryptology Science and Technology, Beijing Electronic Science and Technology Institute, Beijing 100070, China

Mathematics, 2025, vol. 13, issue 22, 1-10

Abstract: The Enhanced Cipher Block Chaining scheme (eCBC) is an authentication encryption scheme (AE) improved from the CBC encryption scheme. It is shown that eCBC scheme fails to achieve ciphertext integrity (INT-CTXT): the IV is unauthenticated and the tag is a linear XOR of ciphertext hashes, enabling trivial forgeries such as IV substitution, block cancellation, and permutation. Furthermore, the medical image application diagonal block encryption based on eCBC scheme is also insecure. Its deterministic design leaks structural information, breaking confidentiality (IND-CPA). At the same time, it also inherits the forgery weaknesses of eCBC scheme, breaking authenticity. The results highlight that neither eCBC scheme nor its application meet AE security goals. And it is recommended to use standardized AE schemes such as SIV, GCM, or Ascon instead of ad hoc designs.

Keywords: authenticated encryption; IND-CPA; INT-CTXT; eCBC (search for similar items in EconPapers)
JEL-codes: C (search for similar items in EconPapers)
Date: 2025
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