# ICRP: Internet-Friendly Cryptographic Relay-Detection Protocol
## 1 Introduction
On a more global scale, Path Aware Networking (PAN) is emerging as a novel way of thinking routing architecture allowing more accurate knowledge on the path traveled by data [16; 17; 18; 19; 20; 21]. An important goal for those architectures is to achieve precise and, above all, trustworthy path tracking of the traversed routers during the sending of a packet. While a complete redesign of the Internet routing architecture might just be the perfect long-term solution, there is still a long way before a worldwide suitable design makes it to standardization. **Our Contribution. **  
1. We approach the detection of relay attacks by using time measurement. To the best of our knowledge, this has never been achieved before in the context of Internet communications. 2. We analyze the time stability between two communicating nodes by running intercontinental experiments over 5 months. 3. We propose ICRP: a two-party cryptographic protocol performing simultaneously the sending of messages, the measurements of the timings, the authentication of the receiver and the decision about the legitimacy of the route. The decision process uses a so-called decision function, taking as inputs a sample of measures captured on the fly. The function checks if the sample matches the \"expected behavior\" between the nodes, and outputs a Boolean (1 if the sample is suspicious, i.e., the traffic might be hijacked, 0 otherwise). 4. We implement a prototype to test the performances of our protocol for a large amount of data exchanges (Up to 200 Mo). The remainder of the paper is structured as follows. In Section 2, we analyze time stability over Internet communication and show that this stability is achieved for UDP communications between terminals from different locations, even for intercontinental exchanges. In Section 3, we introduce the function deciding whether a given exchange is suspicious. This decision function outputs a Boolean (1 for suspicious and 0 otherwise). It takes as inputs a freshly collected sample and a so-called \"reference sample\". The reference sample represents the \"expected behavior\" between the nodes and is constructed during a learning phase prior to the first execution of the protocol. We then test the decision function efficiency by observing the false positive and false negative rates over a large group of both genuine communications and relay simulations. In Section 4, we first describe the Distance-Bounding Protocols. They are used in short range contactless communications for two-party authentication [22; 23; 24; 25; 26]. Those protocols achieve authentication while ensuring an upper bound on the distance separating the parties, which highly complexities the possibilities for relay attacks. Secondly, we present our protocol ICRP which translates the idea of Distance-Bounding in the context of Internet communications. In Section 5, we describe our prototype implementation and evaluate the overhead induced by our solution in terms of latency, computational complexity, and packet size. We believe our approach to be innovative and realistic for practical applications, and so, in section 6, we present an illustrative example.