Holistic analysis of mix protocols

Security protocols are often analysed in isolation as academic challenges. However, the real world can require various combinations of them, such as a certified email protocol executed over a resilient channel, or the key registration protocol to precede the purchase protocols of Secure Electronic Transactions (SET). We develop what appears to be the first scalable approach to specifying and analysing mix protocols. It expands on the Inductive Method by exploiting the simplicity with which inductive definitions can refer to each other. This lets the human analyst study each protocol separately first, and then derive holistic properties about the mix. The approach, which is demonstrated on the sequential composition of a certification protocol with an authentication one, is not limited by the features of the protocols, which can, for example, share message components such as cryptographic keys and nonces. It bears potential for the analysis of complex protocols constructed by general composition of others.