SAT Based Attacks on SipHash - Department of Computer Science

iii
Abstract
<strong>SAT</strong> <strong>Based</strong> <strong>Attacks</strong> on SipHash
Santhosh Kantharaju Siddappa
Supervising Professor: Prof. Alan Kaminsky
SipHash is a proposed pseudorandom function (PRF) that is optimized for small message
inputs. It is intended to be used as a message-authentication code (MAC). It uses a 128-bit
secret key to compute the tag of a message. This project uses <strong>SAT</strong> based attacks on the
primitive to perform partial key recovery and compares the effectiveness of these attacks
against standard brute force approach that involves trying all possible combinations for the
key bits.
The primitive is converted into CNF and fed to an off-the-shelf <strong>SAT</strong> solver. The solver uses
clause learning and if satisfiable, returns a set of values for the missing key bits. It also
reports the number of conflicts that occurred before a solution was found. This is repeated
several times for varying number of missing key bits and different versions of SipHash.
It is then compared to the number of attempts to retrieve the missing key bits using brute
force and the results are analyzed to check the effectiveness of <strong>SAT</strong> based attacks.