TLS协议v1.2详解：网络安全与数据加密

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"rfc5246 - TLS协议版本1.2 (2008).pdf" 《TLS协议版本1.2》是2008年发布的一份互联网标准草案，由T.Dierks和E.Rescorla共同撰写，旨在更新和替代先前的TLS 1.1和其他相关版本。该文档详细规定了Transport Layer Security（传输层安全）协议的第1.2版，是网络安全通信的重要组成部分，特别关注于网络数据的加密和安全传输。 TLS协议的主要目的是在互联网上提供通信安全性，防止窃听、篡改以及消息伪造。它使得客户端/服务器应用程序能够进行安全通信，确保信息的机密性、完整性和身份验证。在TLS 1.2版本中，相比之前的版本，主要的区别包括改进的安全算法选择、更好的抵御特定攻击以及对密码套件的更新。文档中包含多个部分，详细阐述了TLS 1.2的各个方面： 1. 引言：介绍了TLS协议的基本概念，以及1.2版本相对于1.1版本的主要改进和变化。 1.1 要求和术语：定义了文档中使用的专业术语和标准要求。 1.2 与TLS 1.1的主要区别：列出新版本中引入的关键变化，包括加密和认证机制的增强。 2. 目标：明确TLS协议设计和实现的目标，包括数据保密、完整性保护和身份验证。 3. 文档目标：阐述了文档的目的和预期的读者群体。 4. 表现语言：详细描述了协议的结构和元素，包括基本块大小、杂项规则、向量定义等，这些都是实现TLS协议所必需的基础知识。 4.1 基本块大小：规定了协议处理数据时的单位大小，这对于理解和实现加密算法至关重要。 4.2 杂项：涵盖了一些与协议操作相关的非特定块大小的细节。 4.3 向量：定义了协议中的数据序列和它们在安全操作中的作用。 4.4... （部分内容未给出，此处省略）此外，TLS 1.2还规定了握手协议、记录协议、密码套件选择、认证方式、密钥交换机制以及错误处理等多个核心组件，以确保通信双方能够建立安全连接并进行安全的数据交换。TLS 1.2支持多种加密算法和散列函数，如AES、SHA-256等，这些算法的灵活性和强度是其安全性的基石。《TLS协议版本1.2》是互联网通信安全的基石，它的规范为全球网络应用提供了标准的安全框架，确保了用户数据的隐私和通信的可靠性。随着技术的发展，TLS协议不断演进，但TLS 1.2仍然是许多系统和应用广泛采用的安全标准。

RFC 5246

TLS August 2008

Implementations MUST NOT send record types not defined in this

document unless negotiated by some extension. If a TLS

implementation receives an unexpected record type, it MUST send an

unexpected_message alert.

Any protocol designed for use over TLS must be carefully designed to

deal with all possible attacks against it. As a practical matter,

this means that the protocol designer must be aware of what security

properties TLS does and does not provide and cannot safely rely on

the latter.

Note in particular that type and length of a record are not protected

by encryption. If this information is itself sensitive, application

designers may wish to take steps (padding, cover traffic) to minimize

information leakage.

6.1. Connection States

A TLS connection state is the operating environment of the TLS Record

Protocol. It specifies a compression algorithm, an encryption

algorithm, and a MAC algorithm. In addition, the parameters for

these algorithms are known: the MAC key and the bulk encryption keys

for the connection in both the read and the write directions.

Logically, there are always four connection states outstanding: the

current read and write states, and the pending read and write states.

All records are processed under the current read and write states.

The security parameters for the pending states can be set by the TLS

Handshake Protocol, and the ChangeCipherSpec can selectively make

either of the pending states current, in which case the appropriate

current state is disposed of and replaced with the pending state; the

pending state is then reinitialized to an empty state. It is illegal

to make a state that has not been initialized with security

parameters a current state. The initial current state always

specifies that no encryption, compression, or MAC will be used.

The security parameters for a TLS Connection read and write state are

set by providing the following values:

connection end

Whether this entity is considered the "client" or the "server" in

this connection.

PRF algorithm

An algorithm used to generate keys from the master secret (see

Sections

5 and 6.3).

Dierks & Rescorla Standards Track [Page 16]

RFC 5246

TLS August 2008

struct {

ConnectionEnd entity;

PRFAlgorithm prf_algorithm;

BulkCipherAlgorithm bulk_cipher_algorithm;

CipherType cipher_type;

uint8 enc_key_length;

uint8 block_length;

uint8 fixed_iv_length;

uint8 record_iv_length;

MACAlgorithm mac_algorithm;

uint8 mac_length;

uint8 mac_key_length;

CompressionMethod compression_algorithm;

opaque master_secret[48];

opaque client_random[32];

opaque server_random[32];

} SecurityParameters;

The record layer will use the security parameters to generate the

following six items (some of which are not required by all ciphers,

and are thus empty):

client write MAC key

server write MAC key

client write encryption key

server write encryption key

client write IV

server write IV

The client write parameters are used by the server when receiving and

processing records and vice versa. The algorithm used for generating

these items from the security parameters is described in

Section 6.3.

Once the security parameters have been set and the keys have been

generated, the connection states can be instantiated by making them

the current states. These current states MUST be updated for each

record processed. Each connection state includes the following

elements:

compression state

The current state of the compression algorithm.

cipher state

The current state of the encryption algorithm. This will consist

of the scheduled key for that connection. For stream ciphers,

this will also contain whatever state information is necessary to

allow the stream to continue to encrypt or decrypt data.

Dierks & Rescorla Standards Track [Page 18]

RFC 5246

TLS August 2008

version

The version of the protocol being employed. This document

describes TLS Version 1.2, which uses the version { 3, 3 }. The

version value 3.3 is historical, deriving from the use of {3, 1}

for TLS 1.0. (See

Appendix A.1.) Note that a client that

supports multiple versions of TLS may not know what version will

be employed before it receives the ServerHello. See

Appendix E

for discussion about what record layer version number should be

employed for ClientHello.

length

The length (in bytes) of the following TLSPlaintext.fragment. The

length MUST NOT exceed 2^14.

fragment

The application data. This data is transparent and treated as an

independent block to be dealt with by the higher-level protocol

specified by the type field.

Implementations MUST NOT send zero-length fragments of Handshake,

Alert, or ChangeCipherSpec content types. Zero-length fragments of

Application data MAY be sent as they are potentially useful as a

traffic analysis countermeasure.

Note: Data of different TLS record layer content types MAY be

interleaved. Application data is generally of lower precedence for

transmission than other content types. However, records MUST be

delivered to the network in the same order as they are protected by

the record layer. Recipients MUST receive and process interleaved

application layer traffic during handshakes subsequent to the first

one on a connection.

6.2.2. Record Compression and Decompression

All records are compressed using the compression algorithm defined in

the current session state. There is always an active compression

algorithm; however, initially it is defined as

CompressionMethod.null. The compression algorithm translates a

TLSPlaintext structure into a TLSCompressed structure. Compression

functions are initialized with default state information whenever a

connection state is made active. [

RFC3749] describes compression

algorithms for TLS.

Compression must be lossless and may not increase the content length

by more than 1024 bytes. If the decompression function encounters a

TLSCompressed.fragment that would decompress to a length in excess of

2^14 bytes, it MUST report a fatal decompression failure error.

Dierks & Rescorla Standards Track [Page 20]

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