| 6.2 |  | IOS Cryptosystem |
| 6.2.3 |  | Asymmetric encryption |

| Asymmetric encryption is often referred to as public key encryption. It can use either the same algorithm, or different but complementary algorithms to scramble and unscramble data. The required public key and a private key are different, but related. For example, if Alice and Bob want to communicate using public key encryption, both need a public key and private key pair. Alice has to create her public key/private key pair, and Bob has to create his own public key/private key pair. When communicating with each other securely, Alice and Bob use different keys to encrypt and decrypt data.

The mechanisms used to generate these public/private key pairs are complex, but they result in the generation of two very large random numbers. One of which becomes the public key and the other becomes the private key. Because these numbers, as well as their product, must adhere to stringent mathematical criteria to preserve the uniqueness of each public/private key pair, generating these numbers is fairly processor intensive.

Some of the more common public key algorithms are the Rivest-Shamir-Adleman (RSA) algorithm and the El Gamal algorithm. Public key encryption algorithms are rarely used for data confidentiality because of their performance constraints. Instead, public key encryption algorithms are typically used in applications involving authentication using digital signatures and key management.

RSA is the public key cryptographic system developed by Ron Rivest, Adi Shamir, and Leonard Adleman. The two methods are RSA signatures and RSA encryption . RSA encryption generates a value known as a nonce. A nonce is temporary random string, which is generated and combined with the peer public key. This is more secure than the shared key method of authentication. However, it requires more processing power and decreases throughput performance. An RSA signature is the method that uses digital certificates. This method is very scalable and typically is used by medium and large corporations.

Non-repudiation is the ability to prove a transaction occurred, similar to a signed package received from a shipping company. This is very important in financial transactions and similar data transactions. RSA signatures provide non-repudiation. RSA encryption does not provide non-repudiation.

| Web Links RSA Cryptography FAQ http://www.rsasecurity.com/rsalabs/faq/