What is PKI? Public key cryptography is one mechanism that is often used to fulfill the security requirements necessary to conduct electronic transactions over public networks. PKI (public key infrastructure) and cryptography based solutions are taking the lead in secure e-commerce. PKI addresses nonrepudiation of identity using a dual-key encryption system that allows users to uniquely sign documents with a digital signature. Public key cryptography uses pairs of keys, each pair consisting of one public key and one private key. Information encrypted with one key in the pair can only be decrypted with the other key. Alice (the subscriber) attaches a digital signature to a document using her own encryption key (the private key). This has a counterpart (the public key), which anyone may use to confirm that the digital signature was signed with the corresponding private key. A PKI enables users of a public network such as the Internet to exchange data and undertake financial transactions securely and privately. By binding Alice's identity to her public key in a digital certificate, a trusted third party known as a certification authority (CA) allows Bob to verify that Alice signed the document. Under the American Bar Association's Digital Signature Guidelines, a court will presume that Alice did sign the document unless she can prove otherwise. This digital signature system also uses a hash process to verify the what attribute of the electronic document. It does so through the use of a pair of cryptographic keys, a so-called "public key" and a "private key", to encrypt and decrypt messages using a common cryptographic algorithm. The public key is distributed widely within a digital certificate, which has been endorsed by a trusted authority to authenticate the owner. The private key, however, is closely held by you the end user, and is never shared with anyone or sent insecurely across the Internet. Thus, when you, an e-commerce customer encrypt your private information using your private key, the Web server can decrypt your message using your public key. Since your private key is unique and unlike any other key the message could only have come from you. Think of it like a secure safe deposit box that stores all your private information. The safe deposit box requires two keys to open. One key you control, the other key is held by the e-commerce retailer. No one can access or view your account information without your key.