Web Security and Commerce

SSL 3.0 Protocols

SSL protocols are specific types of messages that are sent using the record layer. SSL v3.0 defines three protocols:

• Alert protocol

• ChangeCipherSpec protocol

• Handshake protocol

The SSL record layer can also be used to send user data.

Alert Protocol

Alerts are a specific type of message that can be transmitted by the SSL record layer. Alerts consist of two parts: an AlertLevel and an AlertDescription. Both are coded as single 8-bit numbers.

SSL alerts are encrypted and compressed.

The SSL v3.0 specification defines two alert levels:

Alert Level	Level Name	Meaning
1	Warning	SSL warnings indicate a problem that is not fatal.
2	Fatal	SSL fatal alerts immediately terminate the current SSL session.

SSL v3.0 defines 13 alert descriptions:

Alert Number	Alert Name	Meaning
0	close_notify	Indicates that the sender will not send any more information. If a close_notify is sent with a warning alert level, the session may be resumed. If a close_notify is sent with a fatal alert level, the session may not be resumed.
10	unexpected_message	Inappropriate message was received. This alert should never occur; it indicates an error in one of the SSL implementations participating in the conversation.
20	bad_record_mac	Sender received a record with an incorrect MAC. Fatal.
30	decompression_failure	Information in the record would not properly decompress. Fatal.
40	handshake_failure	Indicates that the sender was unable to negotiate an acceptable set of security parameters—for ...