= Computer security
{scope}
{title2=A12073W1}
Solutions to all three questions of the examination dated 15 June 2015. The cover permits candidates to answer two questions.<Computer Security examination paper by the University of Oxford (2015)>[Cover, A12073W1; questions on printed pages 2–7]{ref}
The <authentication> claims in Question 2 require particular care: the printed third message permits substitution of Bob's key ticket after his <cryptographic nonce> becomes public. The solutions distinguish the intended freshness argument from the <Dolev-Yao model> attack that defeats Bob's <authentication>. This is a property of the printed <protocol>, rather than a missing part of the source.
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