Secure Hash:

A process which reduces a message of arbitrary length to a fixed length fingerprint which is very unlikely to be the same for any other message. The word "secure" indicates that the algorithm has been chosen so that it is not possible to forge a message which to have given hash value, nor to create two similar messages with the same hash value.

Session Key:

A key used for just one message or set of messages. In a typical system, a random session key is generated for use with a symmetric algorithm to encode the bulk of the data, and only the session key itself is communicated using public key encryption.

Server Signature:

The string usually returned as part of servicing each http request that gives the name and version of the web server software being used.

SET:

SET is a secure protocol designed by MasterCard and Visa to facilitate financial transactions over the Internet. Compared with SSL, it places more emphasis on validating both parties to the transaction. SET is still in development, and is not yet widely available.

SHA (Secure Hash Algorithm):

A secure hash, or message digest algorithm adopted as a Federal Information Processing Standard.

SHTTP:

Secure Hypertext Transfer Protocol, provides security at the document level rather than the connection level as provided by SSL. This protocol is not widely used.

SSL (Secure Socket Layer):

A protocol developed by Netscape for encrypted transmission over TCP/IP networks. It sets up a secure end-to-end link over which http or any other application protocol can operate. The most common application of SSL is https for ssl-encrypted http.

SSLeay:

A freely available implementation of the SSL protocol and the cryptographic algorithms used by SSL, developed by Eric Young in Australia. It is naturally available worldwide without breaching United States export legislation, and has become a cornerstone for cryptography application developers wishing to avoid the implications of US export regulations. Usage within the United States has not been legally tested but is likely to be controversial because of the US patent on RSA. Eric Young has now withdrawn from the project and further development is continued under the name OpenSSL by a team of developers.