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On the Security of a MAC by Mitchell
Tetsu IWATA Kaoru KUROSAWA
Publication
IEICE TRANSACTIONS on Fundamentals of Electronics, Communications and Computer Sciences
Vol.E88-A
No.1
pp.25-32 Publication Date: 2005/01/01 Online ISSN:
DOI: 10.1093/ietfec/e88-a.1.25 Print ISSN: 0916-8508 Type of Manuscript: Special Section PAPER (Special Section on Cryptography and Information Security) Category: Symmetric Key Cryptography Keyword: message authentication code, OMAC, security proofs, security gap, pseudorandom permutation,
Full Text: PDF>>
Summary:
OMAC is a provably secure MAC scheme proposed by Iwata and Kurosawa. NIST currently intends to specify OMAC as the modes recommendation. In August 2003, Mitchell published a note "On the security of XCBC, TMAC and OMAC" to propose a new variant of OMAC. We call it OMAC1". In this paper, we prove that OMAC1" is less secure than the original OMAC. We show a security gap between them. As a result, we obtain a negative answer to Mitchell's open question--OMAC1" is not provably secure even if the underlying block cipher is a PRP. Further, we point out limitations of discussion in [16].
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