Geoencryption with Loran Di Qiu, Sherman Lo, Per Enge, Stanford University BIOGRAPHY The prototype of geoencryption demonstration was built and further refinements are needed. To accomplish the Di Qiu is a Ph.D. candidate in Aeronautics and second task, an attack model is developed and analyzed. Astronautics working in the Global Positioning System In this attack model we discussed all the possible attacks (GPS) Laboratory, Stanford University. Her Research that might weaken the protocol and means to defeat these interests are geoencryption and signal authentication. She attacks. received a B.S. in Aerospace Engineering from UCLA and a M.S. in Aeronautics and Astronautics from Stanford This paper describes the work on analyzing system University. performance using the designed attack model. In addition, this paper also provides preliminary results on the size of Dr. Sherman Lo is currently a research associate at the the geotag derived from Loran location-based parameters, Stanford University Global Positioning System (GPS) which limits the security level of the system. Laboratory. He is the Associate Investigator for the Stanford University efforts on the Department of Keywords: geoencryption, Loran, authentication, security Transportation's technical evaluation of Loran. He has received the International Loran Association (ILA) INTRODUCTION President’s Award. He received his Ph.D. in Aeronautics and Astronautics from Stanford University. Traditional encryption is used to provide assurance that only authorized users can use the secure content. Professor Per Enge is a Professor of Aeronautics and However, there are circumstances where the security Astronautics at Stanford University, where he is the provided by traditional encryption is not adequate. In Kleiner-Perkins, Mayfield, Sequoia Capital Professor in traditional cryptosystems, user encryption is based on the School of Engineering. He directs the Stanford GPS possession of secret keys, which falls apart if the keys are Research Laboratory. Enge has received the Kepler, not kept secret (i.e., shared with non-legitimate users). Thurlow, and Burka Awards from the Institute of Furthermore, keys can be forgotten, lost, or stolen. Navigation. He received his Ph.D. from the University of Another type of cryptosystem is password based Illinois. encryption. Most passwords are so simple that they can be easily guessed (especially based on social engineering ABSTRACT methods) or broken by simple dictionary attacks. In many instances, it would still be useful to have an additional The term “geoencryption” or “location-based encryption” layer of security that provides assurance that the secure refer to a security algorithm that limits the access or content can only be used at authorized location and/or decryption of information content to specified locations time [1]. The concept of location based encryption or and/or times. The algorithm does not replace any of the geoencryption is being developed for such a purpose. The conventional cryptographic algorithms, but instead adds capability has tremendous potential benefits to an additional layer of security. Loran is chosen as a case applications such as managing classified/secure data and study to implement geoencryption due to its many digital movie distribution where controlling access is the properties that are beneficial to this protocol. Loran’s predominate concern. stationary transmitters result in many location dependent parameters. Low frequency and high power signal can To implement geoencryption, in principle, a device reach places like urban canyons and indoor environments. performing the decryption integrates a location sensor and Enhanced Loran can provide a data channel useful for cryptographic algorithms. Different radio frequency (RF) geoencryption. signals were studied and compared. Loran was chosen as a case study due to its potentials to geoencryption. A In order to evaluate the effectiveness of Loran for practical concern for implementing this device is whether geoencryption we need to perform two tasks: 1) build a it can be made resistant to unauthorized use and testbed to implement geoencryption protocol, and 2) “tampering”. By tampering, we mean both physical examine the performance and security of the system. attacks on the hardware and attacks on the geoencryption algorithm can be used to ensure that film implementation such as spoofing. If the device is cannot be retrieved except at the theater by authorized vulnerable to tampering, it may be possible to for an personnel who are located at the specified location. adversary to modify it and bypass the location check [2]. This paper further investigates the performance and security of geoencryption protocol. The structure of the paper is as follows. It first gives a brief review on geoencryption and how the protocol builds on conventional cryptographic algorithms and provides an additional layer of security. The paper then describes how we develop an attack model to evaluate the vulnerabilities of the protocol and means to solve these vulnerabilities. As security of geoencryption depends on not only the design and implementation of the protocol but also characteristics of location-based parameters, several parameters are measured and analyzed. This paper then discusses some preliminary results on measuring location information and concludes with future directions of the research. Figure 1: Geoencryption Overview BACKGROUND Loran as a Case Study Geoencryption and Its Application Loran has many characteristics that can be used to Geoencryption is the use of position navigation and time generate a robust geotag. Additionally, it is being (PNT) information as means to enhance the security of a modernized to a next generation system known as traditional cryptographic system. The information is used enhanced Loran (eLoran), which will have a data channel to generate an additional security verification tag, a that can benefit its use for geoencryption [4]. The “geotag”, that is necessary to access the encrypted data or modernization will also reduce the amount of variation in application. some of the location-based parameters. Possible applications of geoencryption are digital film Loran is transmitted from static transmitters and, as a distribution and data security. In this paper, we will use result, there are many parameters that are location digital film distribution as an example to explain the dependent. This is important as the security strength of concept of geoencryption. The idea of geoencryption and the geolock is derived from the information content or its use in digital film distribution was proposed and randomness of the information used to generate it. In developed by Logan Scott, Dr. Dorothy Denning, and addition, Loran has good repeatable accuracy in position, their colleagues at Geocodex [1]. The overview of the which benefits the design of the geolock. Third, Loran is modified system is shown in Figure 1. This modified a high power low frequency signal. This means it is hard system uses geotag as a location verification. Traditional to spoof and hard to jam. Furthermore, the signal can encryption is an integral part of the system. Geotag is reach some places such as urban canyons and indoor derived from specific user location (and time) dependent environment that may not be reachable by a line of sight parameters by quantizing these parameters into grid system such as GPS. Finally, modernized Loran has a spaces. The detailed description of geoencryption is data channel that can carry authentication and time discussed previously in [3]. messages, which will be discussed in details in the later section. Under this system a content provider (“sender”) distributes the encrypted film (ciphertext) to an authorized SECURITY ANALYSIS user (“recipient”). This is done via many methods (such as satellite data links) and, as such, may be readily The security analysis of a protocol is complicated as there available to unauthorized users. The goal is to provide are no standard metrics to precisely quantify the subject encrypted films a location tag that is decryptable only at a of security. To judge the performance and security of the specified location (theaters) and times. The goal is for the geoencryption protocol, we developed an attack model. decryption process to fail and not reveal information An attack model should provide possible failure modes about the plaintext should there be an attempt to decrypt due to the availability of the system. Furthermore, an the data at another location, this should be true whether it attack model defines all possible attacks that might is by an authorized or unauthorized user. Therefore, the threaten the system. Whether a given systems is secure or not can depend dramatically on the attack model is TESLA is implemented to provide the source considered. authentication of the RF navigation signal. TESLA uses symmetric authentication mechanism by appending Message Authentication Code (MAC) at the end of each Security message, which is transmitted from a sender to a receiver, and time (delayed key disclosure) to achieve asymmetry property required for a secure broadcast authentication [5]. Protocol Vulnerabilities Location Information Content MAC is a cryptographic function and is employed in several widely used security algorithms and protocols. Figure 2: Security Analysis Outline Enhanced Loran will transmit data via a data channel, In cryptography, if there are no analytic attacks or which can be used to carry authentication