Ad Hoc Networks

1. Ad Hoc Networks Curtis Bolser Miguel Turner Kiel Murray

2. Towards Flexible Credential Verification in Mobile Ad-hoc Networks - Goals • “To propose a flexible verification mechanism to ascertain a user’s identity and credentials based on assertions from peers.” • Similar to PGP’s web-of-trust concept. • Lessen the number of signature verifications needed. • Allow interoperability between different certificate formats and paradigms (X.509, PGP, SPKI).

3. Towards Flexible Credential Verification in Mobile Ad-hoc Networks – Requirements • Due to generation and verification of credentials and assertions, significant processing power may be required. • For X.509 and SPKI verification, a connection to a wired or fixed network is required. • The devices must have enough space to store a public key ring and trustworthiness levels for each key.

4. Towards Flexible Credential Verification in Mobile Ad-hoc Networks – Architecture • The general architecture is shown in the following figure. Verification Module Security Assertion Module XML Credential Generator Key Management • Key management: Public keys can be added provided their validity has been checked beforehand. • Only assertions made from trusted keys in the ring are considered , all other assertions are discarded. • Four trust levels; Full, Partial, Untrustworthy, Unknown.

5. Towards Flexible Credential Verification in Mobile Ad-hoc Networks – Architecture • XML Credential Generator: Used to create Credential Assertion Statements (CAS) by grouping the user’s credentials together. • Information in X.509 certificates and SPKI are extracted and then converted into XML form to produce the CAS. • The CAS itself need not be encrypted, but it is signed. • Contains X.509 certificate data and attribute certificate data through <X509Data> and <AttributeData> tags in the XML document. • The <X509Certificate> tag denotes where the certificate is stored in its original form (ASN.1 DER encoded)

6. Towards Flexible Credential Verification in Mobile Ad-hoc Networks – Architecture • Security Assertion Model: Main functionality is to issue assertions to other peers after successfully verifying the credentials listed in the CAS. • This is done through Assertion Signature Statements (ASS) which are distributed to the Ad-hoc network. • Peers must have explicitly declared trust of the issuer of the ASS for it to be considered. • More trusted nodes would lead to more ability to validate credentials via peers in the Ad-hoc network instead of through Credential Authorities via a wired network.

7. Towards Flexible Credential Verification in Mobile Ad-hoc Networks – Architecture • Verification Module: Used to determine if the CAS is authentic and based on authentic credentials. • Checks the signatures in the ASSs corresponding to the CAS against the key ring to determine trust. • Trust relationships are not transitive except in the case of partially verified information. • Ex: Node A trusts Node B, Node B trusts Node C. Node C asserts that node L’s credential is valid. • If Node A can partially validate L’s credential, it can trust it due to trusting Node B which trusts Node C. • Does NOT imply trust of further assertions from Node C.

8. Ad Hoc Sensor Networks • Authentication • Typically requires high levels of computational and communication capabilities • Sensors • Low-powered, mobile devices • Many applications for sensors where strong authentication is desirable

9. Three-tier Hierarchy • Tier 1: Access Points • High-power • Route radio packets to wired infrastructure • Tier 2: Forwarding Nodes • Medium-power, mobile • Relay information to access points • Tier 3: Sensor Nodes • Low-power, mobile • Collect data to send to application

10. Authentication • TESLA Certificate • Short lifetime • Sensors assigned certificates by access points • Forwarding nodes only authenticate themselves in assured mode

11. Authentication • Weak mode • Only the origin of the data is verified • The data can be routed through any series of forwarding nodes • Assured mode • Each forwarding node will append its signature to the data • This allows the route to be verified

12. Mobility Helps Security in Ad Hoc Networks – Idea • Mimic human behavior; to communicate securely get close to each other and establish mutual credentials. • Two separate models: • 1 – Allows for security without any kind of central authority. • 2 – Allows for an offline authority authorizing nodes to join the network.

13. Mobility Helps Security in Ad Hoc Networks – Assumptions • The ability to establish a “secure side channel,” through an infrared link, physical connection, or some other secure, local method for model 1. • Nodes in a given Ad Hoc network move around. • This mobility will actually assist in establishing security associations between nodes on the network. • Each node is able to generate cryptographic keys, check signatures, and accomplish any task required to secure its communications (specifically; agree on cryptographic protocols with other nodes)

14. Mobility Helps Security in Ad Hoc Networks – Overview 1 • Network is fully self-organized (no infrastructure, no central authority, no centralized trusted third party). • Secure side channel is used to set up security associations between nodes by exchanging cryptographic material. • This exchange is made by both users consciously and simultaneously (associate a “human face” with the established security association). • Use of “Friends” to further distribute public keys.

15. Mobility Helps Security in Ad Hoc Networks – Overview 2 • Ad Hoc network with a central authority (off-line). • Central Authority controls network membership, deciding which nodes can join and how. • Each node has a unique identity, assigned to it by the authority, binding the node’s identity and public key. • Each node holds the public key of the central authority. • If a node A possesses a certificate signed by the central authority binding node B and its public key, then there is a one-way security association between node A and B. • If each node has a one-way security association of the other, they have a two-way security association.

16. Mobility Helps Security in Ad Hoc Networks – Comparisons • Mobility-based approach allows insertion of new nodes and secure transfers without on-line key distribution. • Drawback: takes time to establish security associations. • Self-organized approach is useful in securing personal communications on the application level. • Offline authority approach useful in securing networking mechanisms such as routing. • In the self-organized approach, users must establish security associations consciously; In the authority-based approach, these associations are established automatically.

17. Generic Implementation of Elliptic Curve Cryptography using Partial Reduction • Elliptic curve cryptography (ECC) is becoming an attractive alternative to traditional RSA and DH • Elliptic Curve Digital Signature Algorithm (ECDSA) • Government a big fan • Paper outlines hardware and software approach to implementing ECC

18. ECC • Security per bit rivals other common cryptosystems • Involves modular addition, multiplication, and division • Coupled with partial reduction, selection of curves becomes more flexible

19. Self-Organized Network-Layer Security in Mobile Ad Hoc Networks • Assumes no initial trust, no central trusting entity • Based on On-demand Distance Vector (AODV) routing protocol • Path discovery is on-demand • Uses Route request/response packets • Is susceptible to routing updates misbehavior and packet forwarding misbehavior

20. Self-Organized Network-Layer Security in Mobile Ad Hoc Networks • Goals • No central trust authority or key distributor • Tolerant to the existence of compromised nodes • Isolate the attacker • Credit based system where nodes will incur less security overhead as time passes

21. Self-Organized Network-Layer Security in Mobile Ad Hoc Networks • How it works • Each node has a token signed by the system key (SK) • This token will expire without renewing it in a timely manner • Bad tokens are known to all nodes via their Token Revocation Lists

22. Self-Organized Network-Layer Security in Mobile Ad Hoc Networks • How it works • Nodes collaborate to monitor each other and issue new tokens • Only when the group decides a node is an attacker is it isolated from the network