GNUnet

3 Acknowledgements Anne-Marie Kermarrec, Tanja Lange, George Danezis, Joe Cannataci and Sad- dek Bensalem have accepted to participate on the jury for my habilitation. I feel very lucky and honored, and thank them for that. I especially thank Tanja Lange for detailed and constructive comments. I am grateful to and for the GNU project, in particular Richard Stallman and Werner Koch, for their long-standing and loud support for me and my projects. I thank all of the Free Software developers, in particular the hundreds of people that have contributed directly to GNUnet over the years. All parts of this document stem from some type of collaboration and the text is based on the respective papers written with various co-authors, in particu- lar my PhD students Nathan Evans, Matthias Wachs, Sree Harsha Totakura, Bartlomiej Polot, Alvaro Garcia-Recuero and Florian Dold. I thank Hernˆani Marques for proofreading the entire document. I also specifically want to thank developers from other projects sharing our goals and values, in particular I2P and Tor. Our discussions with them have been frequently insightful and I hope we will continue to productively work together in the future. Finally, the GNUnet project would not be where it is today without the support by NLnet, the DFG (ENP GR 3688/1-1) and the Renewable Freedom Foundation. Chapter 1 Introduction Internet protocols need a general overhaul to make them suitable as the main communication infrastructure for a sustainable civil liberal society. When the US military created the Internet, the fundamental goal was to interconnect existing networks, which was a simple practical objective. What is more lasting were the second level goalsin order of importanceas elaborated by David Clark in [Cla88]: 1. Internet communication must continue despite loss of networks or gate- ways. 2. The Internet must support multiple types of communications service. 3. The Internet architecture must accommodate a variety of networks. 4. The Internet architecture must permit distributed management of its re- sources. 5. The Internet architecture must be cost-effective. 6. The Internet architecture must permit host attachment with a low level of effort. 7. The resources used in the internet (sic) architecture must be accountable. We note that the only security-related goals relate to availability and usability. While some Internet architects were aware of encryption due to their proximity to the NSA, encryption was classified and thus could not even legally be included in the emerging Internet design that was deliberately non-classified. As a result of these 1970 design goals, the lack of data protection remains visible at all layers of the Internet architecture today. Figure 1.1 shows the design of the IPv4 header from 1981, which is still in use today. It unnecessar- ily leaks information about the sender address and the encapsulated transport protocol. Additionally, the checksum is insufficient to provide authenticity, and it is difficult to prove ownership of a destination address. 11 12CHAPTER 1. INTRODUCTION VersionHDLToSLength IdentificationFlagsFragment offset TTLT. ProtocolChecksum Source IP address Destination IP address Options (optional) Data (Length–HDL bytes) Figure 1.1: The IPv4 header (Sept. 1981) 1.1 The need for private communication Today, the actual use and thus the social requirements for a global network differs widely from those goals of 1970. While the Internet remains suitable for military use, where the network equipment is operated by a command hierarchy and when necessary isolated from the rest of the world, the situation is less tenable for civil society. Due to fundamental Internet design choices, Internet traffic can be misdi- rected, intercepted, censored and manipulated by hostile routers on the net- work. And indeed, the modern Internet has evolved exactly to the point where, as Matthew Green put it, “the network is hostile”. 1 1.1.1 Authenticated encryption With the emerge