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DTEND:20230221T120000Z
UID:6a55797c72b106054fc27473d5fcaa78-409
DTSTAMP:19700101T120016Z
DESCRIPTION:Time-SpaceTradeoffs for Collisions in Hash Functions
URL;VALUE=URI:https://www.csa.iisc.ac.in/newweb/event/409/time-spacetradeoffs-for-collisions-in-hash-functions/
SUMMARY:Cryptographic hash functions are functions that take arbitrary length inputs and output fixed length digest. They are one of the most important cryptographic primitives and widely used in applications today. Apart from the compression requirement, the applications using these functions could need additional properties to be provably secure. One such, perhaps the most important property is collision resistance. 

This property has been well studied for uniform adversaries. However, uniform adversaries fail to capture many real-world adversaries. Hence, several recent works have studied the collision resistance property for non-uniform adversaries. Analyzing non-uniform adversaries presents several challenges. That is why Dodis et al in their EUROCRYPT 18 paper presented a reduction to another (easier to analyze) model named Bit-fixing model.

In our CRYPTO 20 paper, we showed that adversaries in this Bit-fixing model are too strong when the length of the collisions are bounded. We also showed a reduction to the Multi-instance model, which helped us obtain better results for restricted parameter ranges. In our recent CRYPTO 22 paper, we further explored the relation between the Bit-fixing model and the Multi-instance model and further improved the results with our new findings.

The talk will include some preliminary definitions, detailed description of these models, results and a high level idea of the techniques from all the relevant works.
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