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Glossary

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Secure Sockets Layer (SSL)

Secure Sockets Layer is a program layer created by Netscape

Communications for managing the security of message transmissions in

a network. Netscape’s idea was that the programming for keeping your

messages conﬁdential ought to be contained in a program layer between

higher-level protocols (such as HTTP or IMAP) and the TCP/IP layers

of the Internet. The “sockets” part of the term refers to the sockets

method of passing data between a client and a server program in a

network or between program layers in the same computer.

SSL allows an SSL-enabled server to authenticate itself to an

SSL-enabled client, allows the client to authenticate itself to the server,

and allows both machines to establish an encrypted connection.

These capabilities address fundamental concerns about communication

over the Internet and other TCP/IP networks:

• SSL server authentication allows a user to confirm the identity of a

server. SSL-enabled client software can use standard techniques of

public-key cryptography to check that a server’s certificate and

public ID are valid and have been issued by a certificate authority

(CA) listed in the client’s list of trusted CAs. This confirmation can

be important if, for example, the user is sending a credit card

number over the network and wants to check the receiving server’s

identity.

• SSL client authentication allows a server to confirm a user’s

identity. Using the same techniques as those used for server

authentication, SSL-enabled server software can check that a

client’s certificate and public ID are valid and have been issued by a

certificate authority (CA) listed in the server’s list of trusted CAs.

This confirmation can be important if, for example, the server is a

bank sending confidential financial information to a customer and

wants to check the recipient’s identity.

• an encrypted SSL connection requires all information sent between

a client and a server to be encrypted by the sending software and

decrypted by the receiving software, thus providing a high degree

of confidentiality. Confidentiality is important for both parties to

any private transaction. In addition, all data sent over an encrypted

SSL connection is protected with a mechanism for detecting

tampering — that is, for automatically determining whether the

data has been altered in transit.