l (duplex) connection, one SA connection in each direction. The following elements define an SA connection: SPI or 32-bit Security Parameter Index acts as a virtual circuit identifier in connection oriented protocols like Frame Relay or ATM. Protocol type used for security. Source IP address. The transport mode and the tunnel mode are the two modes that define where the IPSec header is added to the IP packet. In transport mode, the IPSec header is added between the IP header and the rest of the packet and in tunnel mode, the IPSec header is added before the original IP header and a new IP header is added before the IPSec header. IPSec header, IP header, and the rest of the packet consti- tute the payload of the new IP header. Authentication header (AH) protocol and the encapsulating security payload (ESP) protocol are the two protocols defined by IPSec. Authentication header (AH) protocol: Source host authentication and pay- load integrity carried by the IP packet are carried out by the AH protocol. But it does not provide privacy. Using a hashing function and a symmetric key, it calculates a message digest and inserts the digest in the authentication header. AH is placed in the correct location depending on the transport or tunnel mode. Encapsulating security payload (ESP) protocol: Source host authentication, data integrity, and privacy are provided by the encapsulating security payload (ESP) protocol. Security in the World Wide Web can be met through the security protocol at the transport level known as transport layer security or TLS. The TLS lies between the Secure Communication application layer and the transport layer (TCP). The handshake protocol and the data exchange or record protocol are the two protocols that make up the TLS. Handshake protocol: Apart from defining message exchange between the browser and the server the protocol also defines other communication param- eters. It is responsible for security negotiation and authentication of the server to the browser. Data exchange protocol: It uses a se