Managing Keys in Mobile Ad-Hoc Networks

Instructor: Lyna Griffin

Lyna has tutored undergraduate Information Management Systems and Database Development. She has a Bachelor's degree in Electrical Engineering and a Masters degree in Information Technology.

In this lesson we will understand the significance of key management in a Mobile Adhoc Network. We will understand the different types of keys employed in the system and the different key management techniques used to ensure data security.

Significance of Security keys in Mobile Ad-Hoc Networks

Encryption keys or security keys are defined as a string of bits generated by an algorithm designed to hide/scramble (make unreadable) for intruders and unscramble the data for the authentic user. Key management forms the core of secure communications within the Mobile Ad-Hoc Networks (MANET). Key Management is the administration of encryption keys, responsible for providing safe methods in the creation, deletion, protecting, storing, revocation and backing up security keys in the network.

The nature of the MANET is that it establishes communication between nodes on the network using open medium wireless communication. Nodes can be dynamically connected anytime and anywhere on the network without following any formal pre-defined structure. They also lack any form of centralized monitoring or management point, making the whole interconnected system highly vulnerable to threats. Free host connections and wireless mobility makes the topology of the network unpredictable and continually changing. Figure-1 below depicts an ad-hoc network:

Adhoc Net

For nodes to access the network- initialization, authentication, and secure communication must be established. Authentication (ensuring and confirming the identity of a user or node) is a core security element. We implement this by exchanging unique security keys based on a specific Key Management System.

As nodes dynamically join/leave the network they are assigned different types of keys which determine their scope of data access within the connected system. Therefore, key management - as a function, is the core of secure communication and can also be the weakest link in the network.

Management of Security Keys

As we discussed earlier secure communication within the MANET is established by a unique key management system and secure routing protocols which provide safe corridors of the passage of data between nodes. The major issue with MANETs is their key management. For ease of understanding, we can compare this to the consulate representative at the airport (Key management technique) checking the identity of every passenger, the validity and authenticity of their passports and visas (keys and nodes). Any form of negligence in carrying out his duties could expose the country (the network) to criminals (malicious attacks) and all kinds of unauthorized individuals (unauthorized nodes).

Without some control, even the most sophisticated cryptographic keys (advanced Passport and Visa technologies) are inefficient if not supported by proper management schemes (border security and technology). The efficiency of this checking mechanism (border security) to pick out fake/unauthentic passports and visas (unauthorized nodes), determines the safety of the country (network). In this lesson, we will look at some of the techniques used to manage security keys within a MANET properly.

Types of Security Keys

  1. Symmetric Keys: The sending and receiving nodes use the same keys.
  2. Asymmetric Keys: Two-part keys: These use separate public and private keys. Public keys are used by all to encrypt data and private keys used by individual nodes to decrypt that data.
  3. Group Keys: A single key assigned to a specific group of nodes.

Key Management Techniques

Centralized Key Management

With this technique, we assign a well-trusted node on the network - the complete responsibility of the management of keys. The node is called a Trusted Third Party (TTP). Depending on the implementation, we can use TTP in three different modes.

  • Inline Mode: TTP is active during the communication session between the two users.
  • Online Mode: TTP is active during communication of two users but for only administrative functions.
  • Offline Mode: TTP communicates with both parties before the establishment of communication and remains offline during the communication session. As seen in Figure-2 below.

centralized management

TTP in Symmetric Key Management

With Symmetric Key Management the same keys are used between all sending and receiving nodes. With the implementation of TTP in symmetric key management systems, Key Distribution Centers (KDCs) are the delegated TTP.

  • Key Distribution Centers(KDC): KDC allows two or more nodes, access to a network, by using a unique key generated by the KDC establishing a secure communication channel. This key gives specific nodes special access to a service not made available to others in that symmetric key segment. KDC is suitable for small networks where some requests by the dynamic connection are not overwhelming. The network can be made more secure by generating the keys randomly on the instance of the request.

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