CRC Seminar Series - Ashwin Jha

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Ashwin Jha

Ashwin Jha

CISPA Helmholtz Center for Information Security

3rd November 2022 - 4:00 pm - 5:00 pm (GST)



Reset-Sampling: Fine-tuning the Security of Standardized MACs


Ashwin is a postdoctoral researcher at CISPA. His research interests are primarily in symmetric-key cryptography. Specifically, he works on the design and analysis of symmetric-key modes of operation with an emphasis on obtaining tight provable security bounds.


In this talk, we describe reset-sampling, a novel proof approach that is demonstrably useful in deriving tight security bounds for single-keyed constructions. Specifically, we discuss the application of this approach to two popular and standardized message authentication codes, LightMAC and OMAC. Using reset-sampling, we are able to derive tight security bounds for both LightMAC and OMAC over a large range of message lengths. In practical terms, our security bounds imply that for a 128-bit block cipher, and message lengths up to 64 Gigabyte, both LightMAC and OMAC can process up to 2^{64} messages before rekeying (same as the birthday bound). In comparison, the previous bounds only allow up to 2^{48} messages.

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