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Efficient Protocols For Secure Message Transmission Over Directed NetworksAuthor: Ravi Kishore Vasala Date: 2018-04-26 Report no: IIIT/TH/2018/8 Advisor:Kannan Srinathan AbstractIn a large distributed network of interconnected nodes, the goal of any Secure Message Transmission (SMT) protocol is to securely deliver the sender’s message at the receiver’s end in the presence of a computationally unbounded adversary, that can partially control the network by corrupting some of its nodes (except the sender and the receiver). In the literature, different variants of SMT problem have been studied depending on the type of network model and/or the types of node corruptions. Undirected graph model and directed graph model are two of the most well-studied network models. Different types of node corruptions studied are passive, fail-stop, omission and Byzantine. In passive corruption, the adversary is only allowed to read/eavesdrop the corrupted node. In fail-stop corruption, the adversary can crash the corrupted node at its will. In omission corruption, the adversary can eavesdrop and/or crash the corrupted node. In Byzantine corruption, the adversary fully controls the actions of the corrupted nodes. In an undirected graph setting, for most variants of SMT problem whether the corresponding SMT protocols exist or not is known in the literature. Moreover, whenever a protocol exists, communication efficient protocols have been designed too. Whereas, in directed graph setting very little is known about the existence of protocols (for dif- ferent variants of SMT problem) as well as the design of efficient protocols. This thesis primarily focuses on bridging this gap between undirected and directed graph settings. It is usually difficult to design efficient protocols in arbitrary directed graphs due to the plethora of different cases/possibilities that usually need to be dealt with. However, in the literature due to the simplicity and ease of protocol design, wires model is considered which is a special case of directed graph setting. In wires model, paths (known as wires) from the sender to the receiver and vice-versa are considered whereas the weak paths are discarded. On the other hand, if the intermediate nodes can generate random-coins and/or perform computations, it is known that the directed wires-based abstraction is inadequate to capture arbitrary directed graphs. In this thesis, we design efficient protocols for different variants of SMT problem in both wires model as well as arbitrary directed graph model. Moreover, we introduce a new model namely routing model to answer the following fundamental question. If each intermediate node is a mere router (can not do computations but can route message to its neighbours) then under what condition(s) is given variant of SMT (im)possible? Furthermore, in arbitrary directed graph setting, we design a protocol which is both communication as well as round/hop optimum when the adversary is passive. Full thesis: pdf Centre for Security, Theory and Algorithms |
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