We consider the problem of secret key distribution in a sensor network with multiple scattered sensor nodes and a mobile device that can be used to bootstrap the network. Our main contribution is a set of secure protocols that rely on simple network coding operations to provide a robust and lowcomplexity solution for sharing secret keys among sensor nodes, including pairwise keys, cluster keys, key revocation and mobile node authentication. In spite of its role as a key enabler for this approach, the mobile node only has access to an encrypted version of the keys, providing information-theoretic security with respect to attacks focused on the mobile node. Our results include performance evaluation in terms of security metrics and a detailed analysis of resource utilization. The basic scheme was implemented and tested in a real-life sensor network testbed. We deem this class of network coding protocols to be particularly well suited for highly constrained dynamic systems such as wireless sensor networks.