1. Asymmetric-Key Cryptography Also known as public-key cryptography, performs encryption and decryption with two different algorithms. Each node announces its public key and then uses its own private key to encrypt messages. Other nodes can decrypt the node with the public key. Only the specific public key of a node can be used to decrypt a message encrypted with that node’s private key. Messages can be authenticated, kept private and the content proven to be correct through this method.

2. Symmetric-Key Cryptography Also known as shared-key cryptography, performs encryption and decryption with the same algorithm and key. The difficulty is sharing a key between two nodes without someone else eavesdropping and also receiving the key Schemes must be implemented carefully. Methods such as simple shifts in ASCII code are prone to the “dictionary attack” Traditional symmetric schemes have great difficulty scaling. The number of keys in each node increases on O(n 2 )

3. Sensor Node Characteristics

4. Probabilistic Key Distribution Keeping every key of a large sensor network is unnecessary. Most nodes can not talk directly to each other in a network with 10,000 nodes. The number of keys can be be decreased greatly if we reduce the number per node to guarantee that two nodes can “almost certainly” communicate. In order to implement this, it is important to understand some random graph theory.