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Web Security and Commerce by Gene Spafford, Simson Garfinkel

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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 ...

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