 main public key algorithms: RSA (named for its creators, Rivest, Shamir, and Adelman), Diffie-Hellman, and PGP. RSA is the oldest of the three algorithms, and its security derives from the difficulty of factoring the product of two large prime integers. Diffie-Hellman is used mostly for exchanging keys; its security rests on the difficulty of computing discrete algorithms in a finite field, generated by a large prime number. PGP (www.pgp.com), which was created in 1991, is one of the most popular PKE schemes. Public Key Infrastructure Without a functioning universal public key infra- structure (PKI), we cannot reliably and easily acquire certificates that contain pub- lic keys for persons or organizations we want to communicate with. One of the biggest hurdles e-commerce companies face is confirming the identity of the par- ties involved. Ensuring identity requires an encrypted ID object that can be issued by a mutually trusted third party (i.e., a CA) and then verified and accepted by a user's browser. Personal digital IDs contained in the user's browser accomplish this. Historically, these client certificates have been used to control access to resources on a business network, but they can also contain other user information, including identity discount level or customer type. The user's browser reads the server certif- icate, and if it's accepted, the browser generates a symmetric session key, using the server's public key. The server then decrypts the symmetric key, which is then used to encrypt the rest of the transaction. The transaction is then signed, using the user's digital ID, verifying the user's identity and legally binding the user to the transaction. PKI is a system that provides protocols and services for managing public keys in an intranet or Internet environment; it involves distributing keys in a secure way. PKI secures e-business applications such as private e-mail, purchase orders, and workflow automation. It uses digital certificates and digital signatures to authenticate and encrypt messag