SSL is sn acronym for Secure Sockets Layer, a protocol developed by Netscape Corporation for transmitting private documents via the Internet. SSL uses a cryptographic system that uses two keys to encrypt data — a public key known to everyone and a private or secret key known only to the recipient of the message. All modern browsers support SSL, and many websites use the protocol to securely transmit confidential user information, such as credit card numbers, over the internet. By convention, URLs that require an SSL connection start with https: instead of http:.