A Cryptographic Approach to Preventing Unauthorized Access

Communication through digital means is playing an increasingly important role in our lives. As the exchanged data can often be sensitive or private, special care must be taken to prevent it from being accessed by unauthorized parties. In this thesis, we analyse this problem in several contexts and propose a series of solutions.
We first consider mobile phone networks, where compatibility with lawful interception requests is an immutable constraint. We propose a new primitive called Lawful Interception Key Exchange, or LIKE. LIKE allows for secure channel establishment and increased privacy, while still being lawful interception compliant.
Next, we investigate the privacy of the Transport Layer Protocol version 1.3 (TLS), widely used for secure channel establishment over the internet. We propose a model for privacy and show that TLS 1.3 is privacy-preserving in our model.
Finally, we analyse deep attestation protocols, with a focus on the property of linking. We propose a formal, cryptographic approach to this topic, as well as a new construction.