Security in Mobile Wireless Sensor Networks – A Survey <s> D. Access Control <s> Access control constrains what a user can do directly, as well as what programs executing on behalf of the users are allowed to do. In this way access control seeks to prevent activity that could lead to a breach of security. This article explains access control and its relationship to other security services such as authentication, auditing, and administration. It then reviews the access matrix model and describes different approaches to implementing the access matrix in practical systems, and follows with a discussion of access control policies commonly found in current systems, and a brief consideration of access control administration. > <s> BIB001 </s> Security in Mobile Wireless Sensor Networks – A Survey <s> D. Access Control <s> A key distribution scheme for dynamic conferences is a method by which initially an (off-line) trusted server distributes private individual pieces of information to a set of users. Later any group of users of a given size (a dynamic conference) is able to compute a common secure key. In this paper we study the theory and applications of such perfectly secure systems. In this setting, any group of t users can compute a common key by each user computing using only his private piece of information and the identities of the other t - 1 group users. Keys are secure against coalitions of up to k users, that is, even if k users pool together their pieces they cannot compute anything about a key of any t-size conference comprised of other users.First we consider a non-interactive model where users compute the common key without any interaction. We prove a lower hound on the size of the user's piece of information of (k+t-1 t-1) times the size of the common key. We then establish the optimality of this bound, by describing and analyzing a scheme which exactly meets this limitation (the construction extends the one in [2]). Then, we consider the model where interaction is allowed in the common key computation phase, and show a gap between the models by exhibiting an interactive scheme in which the user's information is only k + t - 1 times the size of the common key. We further show various applications and useful modifications of our basic scheme. Finally, we present its adaptation to network topologies with neighborhood constraints. <s> BIB002 </s> Security in Mobile Wireless Sensor Networks – A Survey <s> D. Access Control <s> As more sensitive data is shared and stored by third-party sites on the Internet, there will be a need to encrypt data stored at these sites. One drawback of encrypting data, is that it can be selectively shared only at a coarse-grained level (i.e., giving another party your private key). We develop a new cryptosystem for fine-grained sharing of encrypted data that we call Key-Policy Attribute-Based Encryption (KP-ABE). In our cryptosystem, ciphertexts are labeled with sets of attributes and private keys are associated with access structures that control which ciphertexts a user is able to decrypt. We demonstrate the applicability of our construction to sharing of audit-log information and broadcast encryption. Our construction supports delegation of private keys which subsumesHierarchical Identity-Based Encryption (HIBE). <s> BIB003 </s> Security in Mobile Wireless Sensor Networks – A Survey <s> D. Access Control <s> Sensor networks have been an attractive platform for pervasive computing and communication. Due to the lack of physical protection, however, sensor networks are vulnerable to attacks if deployed in hostile environments. When a sensor network is under attack, the most fundamental concern is that information communicated or stored in the network remains safe. The past research has focused on securing information in communication, but how to secure information in storage has been generally overlooked. Meanwhile, distributed data storage and retrieval have become popular for efficient data management in sensor networks, which renders the absence of schemes for securing stored information to be a more severe problem. Hence, we propose in this paper three schemes to deal with the problem. All the schemes have the following properties: (i) only authorized entities can access data stored in the sensor network; (ii) the schemes are resilient to a large number of sensor node compromises. The second and the third schemes do not involve any centralized entity except for a few initialization or renewal operations, and thus support secure, distributed data storage and retrieval. The third scheme further provides high scalability and flexibility, and hence is most suitable in real applications. The effectiveness and efficiency of the proposed schemes have also been verified through extensive analysis and TOSSIM-based simulations <s> BIB004 </s> Security in Mobile Wireless Sensor Networks – A Survey <s> D. Access Control <s> The owner and users of a sensor network may be different, which necessitates privacy-preserving access control. On the one hand, the network owner need enforce strict access control so that the sensed data are only accessible to users willing to pay. On the other hand, users wish to protect their respective data access patterns whose disclosure may be used against their interests. This paper presents DP 2 AC, a Distributed Privacy- Preserving Access Control scheme for sensor networks, which is the first work of its kind. Users in DP 2 AC purchase tokens from the network owner whereby to query data from sensor nodes which will reply only after validating the tokens. The use of blind signatures in token generation ensures that tokens are publicly verifiable yet unlinkable to user identities, so privacy- preserving access control is achieved. A central component in DP 2 AC is to prevent malicious users from reusing tokens. We propose a suite of distributed techniques for token-reuse detection (TRD) and thoroughly compare their performance with regard to TRD capability, communication overhead, storage overhead, and attack resilience. The efficacy and efficiency of DP 2 AC are confirmed by detailed performance evaluations. <s> BIB005 </s> Security in Mobile Wireless Sensor Networks – A Survey <s> D. Access Control <s> We show attacks on several cryptographic schemes that have recently been proposed for achieving various security goals in sensor networks. Roughly speaking, these schemes all use "perturbation polynomials" to add "noise" to polynomialbased systems that offer information-theoretic security, in an attempt to increase the resilience threshold while maintaining efficiency. We show that the heuristic security arguments given for these modified schemes do not hold, and that they can be completely broken once we allow even a slight extension of the parameters beyond those achieved by the underlying information-theoretic schemes. Our attacks apply to the key predistribution scheme of Zhang et al. (MobiHoc 2007), the access-control schemes of Subramanian et al. (PerCom 2007), and the authentication schemes of Zhang et al. (INFOCOM 2008). Our results cast doubt on the viability of using "perturbation polynomials" for designing secure cryptographic schemes. <s> BIB006 </s> Security in Mobile Wireless Sensor Networks – A Survey <s> D. Access Control <s> Distributed sensor data storage and retrieval has gained increasing popularity in recent years for supporting various applications. While distributed architecture enjoys a more robust and fault-tolerant wireless sensor network (WSN), such architecture also poses a number of security challenges especially when applied in mission-critical applications such as battle field and e-healthcare. First, as sensor data are stored and maintained by individual sensors and unattended sensors are easily subject to strong attacks such as physical compromise, it is significantly harder to ensure data security. Second, in many mission-critical applications, fine-grained data access control is a must as illegal access to the sensitive data may cause disastrous result and/or prohibited by the law. Last but not least, sensors usually are resource-scarce, which limits the direct adoption of expensive cryptographic primitives. To address the above challenges, we propose in this paper a distributed data access control scheme that is able to fulfill fine-grained access control over sensor data and is resilient against strong attacks such as sensor compromise and user colluding. The proposed scheme exploits a novel cryptographic primitive called attribute-based encryption (ABE), tailors, and adapts it for WSNs with respect to both performance and security requirements. The feasibility of the scheme is demonstrated by experiments on real sensor platforms. To our best knowledge, this paper is the first to realize distributed fine-grained data access control for WSNs. <s> BIB007 </s> Security in Mobile Wireless Sensor Networks – A Survey <s> D. Access Control <s> For courses in Computer/Network Security. In recent years, the need for education in computer security and related topics has grown dramatically -- and is essential for anyone studying Computer Science or Computer Engineering. This is the only text available to provide integrated, comprehensive, up-to-date coverage of the broad range of topics in this subject. In addition to an extensive pedagogical program, the book provides unparalleled support for both research and modeling projects, giving students a broader perspective. The Text and Academic Authors Association have named Computer Security: Principles and Practice the winner of the Textbook Excellence Award for the best Computer Science textbook of 2008. Visit Stallings Companion Website at http://williamstallings.com/CompSec/CompSec1e.html for student and instructor resources and his Computer Science Student Resource site http://williamstallings.com/StudentSupport.html Password protected instructor resources can be accessed here by clicking on the Resources Tab to view downloadable files. (Registration required) Supplements Include: *Power Point Lecture Slides*Instructor's Manual*Author maintained website . <s> BIB008
Access control is defined as the prevention of unauthorized use of a resource, including the prevention of use of a resource in an unauthorized manner BIB008 . Generally, the data access strategy of WSNs can be divided into two ways, namely access control at the base station and access control at sensor nodes. In traditional WSNs, sensor nodes transmit generated data to a base station that users can access by querying through the base station. Access control strategy is adopted in the base station side rather than in the sensor nodes. Since the base station is not constrained by resources (computation, energy, memory, etc.), many access control policies BIB001 ,  can be used. As this paper focuses mainly on MWSNs, we do not explicitly address the access control strategies of base stations. In MWSNs, as a large amount of sensed data are stored in individual sensor nodes, the data storage and access have to be protected by using encryption, so that the data can only be accessed by authorized users with the corresponding keys. For example, in mission-critical application scenarios (such as a battlefield), different kinds of sensors generate different types of sensed data (e.g., smoke, vibration or noise, etc.), which may be specified to different kinds of users (e.g., scouts, landmine experts or officers, etc.), or can be accessed based on the user's security level. For example, a general may have a higher privilege to access data than a soldier does. To solve the aforementioned problem, related schemes BIB004 - BIB005 have been proposed, and they can be divided into two categories, namely Symmetric Key Cryptography (SKC) based schemes BIB004 and Public Key Cryptography (PKC) based ones BIB007 , BIB005 . In the SKC-based schemes, data is encrypted and decrypted by using the same secret key. This means that if a sensor is compromised, the ADV can get the secret key stored in the sensor memory and is thus able to decrypt the accumulated data generated by the same sensor. To solve this problem, a naive scheme is to divide the lifetime of sensors into a series of phases, and the key used for encrypting the data is updated in each phase. Sensors merely store the key for the current phase, and erase all the previous keys securely. Nevertheless, the interaction may incur high computation overhead. The authors in BIB004 have proposed an SKC-based distributed data storage and retrieval scheme, where the access control policy is provided by sharing the symmetric secret key with authorized users based on perturbed polynomial technique BIB002 . However, the scheme BIB004 was proved as not secure in BIB006 . Thus, distributed data storage access control in MWSNs using SKC-based scheme is still an open question. Next, in the PKC-based schemes, data is encrypted by using a public key, and it can only be decrypted by using the corresponding private key. Thanks to this advantageous feature of PKC, an attacker is not able to decrypt the data stored in the sensors even if the sensors are compromised, since it lacks the corresponding private keys. In traditional PKC-based schemes, however, data encrypted using a public key can be only decrypted by using the corresponding private key, in the sense of a oneto-one relationship. For instance, the encrypted data using a general's public key can only be accessed by the general. If the data is specified to be accessed by users having different security levels (e.g., scouts or landmine experts), the data has to be encrypted by the public keys of the users, which consequently causes large storage overhead and computation overhead. To tackle this problem, the authors in BIB007 proposed Fine-grained Distributed data Access Control (FDAC) scheme based on Key-Policy Attribute-Based Encryption (KP-ABE) BIB003 . The basic idea of KP-ABE is that ciphertext associates with a set of attributes, and private key associates with an access structure. A ciphertext can be decrypted only if the attributes of the ciphertext satisfy the access structure of the private key. As shown in Fig. 5 , a landmine expert with the key which has access structure as {(Location is road) AND (Type is smoke OR vibration) AND (Owner is landmine expert)} can decrypt ciphertext A with attribute {location = road, type = vibration, owner = (landmine expert, scout, general)}, but cannot decrypt ciphertext B with attribute {location = village, type = smoke, owner = (scout, general)}. By using the advantageous property of KP-ABE, in FDAC, each sensor and its sensed data are associated with a set of attributes, and each user is assigned with an access structure which is embedded in its secret key. The leaf node of the access structure tree is one of the attributes in the attribute set. It is easy to observe that the definition of the access structure tree enables one to represent complex logical expressions, and is able to specify access privileges of users in a fine-grained way. Although the authors have tailored and adapted KP-ABE for WSNs and demonstrate that FDAC is affordable compared with high-end sensor nodes such as iMote2, the scheme is still too expensive for normal sensor nodes because KP-ABE is public key cryptography. Figure 5 . A example of access structure in a battlefield scenario.