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Logical Analysis and Verification of Cryptographic Protocols - Loria

Logical Analysis and Verification of Cryptographic Protocols - Loria

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80 CHAPTER 3. PROTOCOLS WITH VULNERABLE HASH FUNCTIONS<br />

3.5.4 Decidability <strong>of</strong> ordered Ih-satisfiability problem<br />

Following the results obtained in [74], <strong>and</strong> by Lemmas 13, 14, 15, 16, 17, 18, 19,<br />

<strong>and</strong> 20, we conjecture that we can reduce the ordered Ih satisfiability problem<br />

to the ordered Ifree satisfiability problem. And hence, we conjecture that the<br />

ordered Ih satisfiability problem is decidable.<br />

3.6 Conclusions<br />

We have analysed here the class <strong>of</strong> cryptographic protocols that use collision<br />

vulnerable hash functions. In order to model such hash functions we have introduced<br />

new symbols to denote the ability to create messages with the same<br />

hash value. This introduction amounts to the skolemisation <strong>of</strong> the equational<br />

property describing the existence <strong>of</strong> collisions. We believe that this construction<br />

can be extended to model the more complex <strong>and</strong> game-based properties<br />

that appear when relating a symbolic <strong>and</strong> a concrete model <strong>of</strong> cryptographic<br />

primitives. It is well-known that hash functions are widely used in the digital<br />

signature schemes which is the topic <strong>of</strong> the next chapter.

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