SSL协议（二）帧格式

TLS record

This is the general format of all TLS records.

+	Byte +0	Byte +1	Byte +2	Byte +3
Byte 0	Content type
Bytes 1..4	Version	Length
(Major)	(Minor)	(bits 15..8)	(bits 7..0)
Bytes 5..(m-1)	Protocol message(s)
Bytes m..(p-1)	MAC (optional)
Bytes p..(q-1)	Padding (block ciphers only)

Content typeThis field identifies the Record Layer Protocol Type contained in this Record.
Content types

Hex	Dec	Type
0x14	20	ChangeCipherSpec
0x15	21	Alert
0x16	22	Handshake
0x17	23	Application
0x18	24	Heartbeat

VersionThis field identifies the major and minor version of TLS for the contained message. For a ClientHello message, this need not be the highest version supported by the client.
Versions

Major version	Minor version	Version type
3	0	SSL 3.0
3	1	TLS 1.0
3	2	TLS 1.1
3	3	TLS 1.2

Length

The length of Protocol message(s), MAC and Padding, not to exceed 214 bytes (16 KiB).Protocol message(s)One or more messages identified by the Protocol field. Note that this field may be encrypted depending on the state of the connection.MAC and PaddingA message
authentication code computed over the Protocol message, with additional key material included. Note that this field may be encrypted, or not included entirely, depending on the state of the connection.No MAC or Padding can be present at end of TLS records before all cipher algorithms and parameters have been negotiated and handshaked and then confirmed by sending a CipherStateChange record
(see below) for signalling that these parameters will take effect in all further records sent by the same peer.

Handshake protocol[edit]

Most messages exchanged during the setup of the TLS session are based on this record, unless an error or warning occurs and needs to be signaled by an Alert protocol record (see below), or the encryption mode of the session is modified by another record (see
ChangeCipherSpec protocol below).

+	Byte +0	Byte +1	Byte +2	Byte +3
Byte 0	22
Bytes 1..4	Version	Length
(Major)	(Minor)	(bits 15..8)	(bits 7..0)
Bytes 5..8	Message type	Handshake message data length
(bits 23..16)	(bits 15..8)	(bits 7..0)
Bytes 9..(n-1)	Handshake message data
Bytes n..(n+3)	Message type	Handshake message data length
(bits 23..16)	(bits 15..8)	(bits 7..0)
Bytes (n+4)..	Handshake message data

Message typeThis field identifies the Handshake message type.

Message types
Code	Description
0	HelloRequest
1	ClientHello
2	ServerHello
4	NewSessionTicket
11	Certificate
12	ServerKeyExchange
13	CertificateRequest
14	ServerHelloDone
15	CertificateVerify
16	ClientKeyExchange
20	Finished

Handshake message data lengthThis is a 3-byte field indicating the length of the handshake data, not including the header.

Note that multiple Handshake messages may be combined within one record.

Alert protocol[edit]

This record should normally not be sent during normal handshaking or application exchanges. However, this message can be sent at any time during the handshake and up to the closure of the session. If this is used to signal a fatal error, the session will be
closed immediately after sending this record, so this record is used to give a reason for this closure. If the alert level is flagged as a warning, the remote can decide to close the session if it decides that the session is not reliable enough for its needs
(before doing so, the remote may also send its own signal).

+	Byte +0	Byte +1	Byte +2	Byte +3
Byte 0	21
Bytes 1..4	Version	Length
(Major)	(Minor)	0	2
Bytes 5..6	Level	Description
Bytes 7..(p-1)	MAC (optional)
Bytes p..(q-1)	Padding (block ciphers only)

LevelThis field identifies the level of alert. If the level is fatal, the sender should close the session immediately. Otherwise, the recipient may decide to terminate the session itself, by sending
its own fatal alert and closing the session itself immediately after sending it. The use of Alert records is optional, however if it is missing before the session closure, the session may be resumed automatically (with its handshakes).Normal closure of a session after termination of the transported application should preferably be alerted with at least the Close notify Alert type (with a simple warning level) to
prevent such automatic resume of a new session. Signalling explicitly the normal closure of a secure session before effectively closing its transport layer is useful to prevent or detect attacks (like attempts to truncate the securely transported data, if
it intrinsically does not have a predetermined length or duration that the recipient of the secured data may expect).
Alert level types

Code	Level type	Connection state
1	warning	connection or security may be unstable.
2	fatal	connection or security may be compromised, or an unrecoverable error has occurred.

DescriptionThis field identifies which type of alert is being sent.
Alert description types

Code	Description	Level types	Note
0	Close notify	warning/fatal
10	Unexpected message	fatal
20	Bad record MAC	fatal	Possibly a bad SSL implementation, or payload has been tampered with e.g. FTP firewall rule on FTPS server.
21	Decryption failed	fatal	TLS only, reserved
22	Record overflow	fatal	TLS only
30	Decompression failure	fatal
40	Handshake failure	fatal
41	No certificate	warning/fatal	SSL 3.0 only, reserved
42	Bad certificate	warning/fatal
43	Unsupported certificate	warning/fatal	e.g. certificate has only Server authentication usage enabled and is presented as a client certificate
44	Certificate revoked	warning/fatal
45	Certificate expired	warning/fatal	Check server certificate expire also check no certificate in the chain presented has expired
46	Certificate unknown	warning/fatal
47	Illegal parameter	fatal
48	Unknown CA (Certificate authority)	fatal	TLS only
49	Access denied	fatal	TLS only – e.g. no client certificate has been presented (TLS: Blank certificate message or SSLv3: No Certificate alert), but server is configured to require one.
50	Decode error	fatal	TLS only
51	Decrypt error	warning/fatal	TLS only
60	Export restriction	fatal	TLS only, reserved
70	Protocol version	fatal	TLS only
71	Insufficient security	fatal	TLS only
80	Internal error	fatal	TLS only
90	User canceled	fatal	TLS only
100	No renegotiation	warning	TLS only
110	Unsupported extension	warning	TLS only
111	Certificate unobtainable	warning	TLS only
112	Unrecognized name	warning/fatal	TLS only; client's Server Name Indicator specified a hostname not supported by the server
113	Bad certificate status response	fatal	TLS only
114	Bad certificate hash value	fatal	TLS only
115	Unknown PSK identity (used in TLS-PSK andTLS-SRP)	fatal	TLS only
120	No Application Protocol	fatal	TLS only, client's ALPN did not contain any server-supported protocols

ChangeCipherSpec protocol[edit]

+	Byte +0	Byte +1	Byte +2	Byte +3
Byte 0	20
Bytes 1..4	Version	Length
(Major)	(Minor)	0	1
Byte 5	CCS protocol type

CCS protocol typeCurrently only 1.

Application protocol[edit]

+	Byte +0	Byte +1	Byte +2	Byte +3
Byte 0	23
Bytes 1..4	Version	Length
(Major)	(Minor)	(bits 15..8)	(bits 7..0)
Bytes 5..(m-1)	Application data
Bytes m..(p-1)	MAC (optional)
Bytes p..(q-1)	Padding (block ciphers only)

LengthLength of application data (excluding the protocol header and including the MAC and padding trailers)MAC20 bytes for the SHA-1-based HMAC,
16 bytes for the MD5-based HMAC.PaddingVariable length; last byte contains the padding length.