Abstract
We present a forgery attack on Prøst-OTR in a related-key setting. Prøst is a family of authenticated encryption algorithms proposed as candidates in the currently ongoing CAESAR competition, and Prøst-OTR is one of the three variants of the Prøst design. The attack exploits how the Prøst permutation is used in an Even-Mansour construction in the Feistel-based OTR mode of operation. Given the ciphertext and tag for any two messages under two related keys K and K ⊕ Δ with related nonces, we can forge the ciphertext and tag for a modified message under K. If we can query ciphertexts for chosen messages under K⊕Δ, we can achieve almost universal forgery for K. The computational complexity is negligible.
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CITATION STYLE
Dobraunig, C., Eichlseder, M., & Mendel, F. (2015). Related-key forgeries for Prøst-OTR. In Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) (Vol. 9054, pp. 282–296). Springer Verlag. https://doi.org/10.1007/978-3-662-48116-5_14
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