On the Security of the CCM Encryption Mode and of a Slight Variant

Pierre-Alain Fouque (1, 2, 3) , Gwenaëlle Martinet (4) , Frédéric Valette (5) , Sebastien Zimmer (1, 2)

1 LIENS - Laboratoire d'informatique de l'école normale supérieure
2 CASCADE - Construction and Analysis of Systems for Confidentiality and Authenticity of Data and Entities
3 ENS-PSL - École normale supérieure - Paris
4 DCSSI/SDS/LTI - Laboratoire des Technologies de l'Information
5 DGA.MI - DGA Maîtrise de l'information

In this paper, we present an analysis of the CCM mode of operations and of a slight variant. CCM is a simple and efficient encryption scheme which combines a CBC-MAC authentication scheme with the counter mode of encryption. It is used in several standards. Despite some criticisms (mainly this mode is not online, and requires non-repeating nonces), it has nice features that make it worth to study. One important fact is that, while the privacy of CCM is provably garanteed up to the birthday paradox, the authenticity of CCM seems to be garanteed beyond that. There is a proof by Jonsson up to the birthday paradox bound, but going beyond it seems to be out of reach with current techniques. Nevertheless, by using pseudo-random functions and not permutations in the counter mode and an authentication key different from the privacy key, we prove security beyond the birthday paradox. We also wonder if the main criticisms against CCM can be avoided: what is the security of the CCM mode when the nonces can be repeated, (and) when the length of the associated data or message length is missing to make CCM on-line. We show generic attacks against authenticity in these cases. The complexity of these attacks is under the birthday paradox bound. It shows that the lengths of the associated data and the message, as well as the nonces that do not repeat are important elements of the security of CCM and cannot be avoided without significantly decreasing the security.

Domaines: Cryptographie et sécurité [cs.CR]

Pierre-Alain Fouque, Gwenaëlle Martinet, Frédéric Valette, Sebastien Zimmer. On the Security of the CCM Encryption Mode and of a Slight Variant. Applied Cryptography and Network Security : 6th International Conference, ACNS 2008, 2008, New York, United States. pp.411-428, ⟨10.1007/978-3-540-68914-0_25⟩. ⟨inria-00556684⟩