IEEE 802.11i安全增强标准详解

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"802.11i是IEEE针对无线局域网（WLAN）安全增强的一个重要标准，它对802.11系列协议进行了修订，特别是在Medium Access Control (MAC)层的安全性方面进行了大幅改进。该标准旨在解决早期802.11无线网络存在的安全漏洞，如WEP（ Wired Equivalent Privacy）加密的不足，以提供更可靠的数据保护和身份验证机制。802.11i引入了WPA（Wi-Fi Protected Access）和后来的WPA2，这两种安全协议已经成为现代WiFi网络的标准配置。" 802.11i协议是在2004年由IEEE发布，作为802.11标准的第六个修正案，它包含了对1999年版802.11标准以及后续的802.11a、802.11b、802.11d、802.11g和802.11h等多个修订版的更新。这个标准主要关注的是MAC层的安全性提升，以确保无线通信的隐私和完整性。在802.11i中，最重要的安全特性是引入了AES（Advanced Encryption Standard）加密算法，取代了原来的WEP中使用的RC4算法。AES提供了更强大的数据加密，使得破解变得更加困难。此外，802.11i还引入了TKIP（Temporal Key Integrity Protocol），这是一个用于WPA的过渡性解决方案，它在不改变原有WEP硬件的情况下增强了加密性能。在身份验证方面，802.11i引入了802.1X标准，这是一种基于端口的网络访问控制协议，允许动态地进行用户认证和授权。结合EAP（Extensible Authentication Protocol），802.1X可以支持多种认证方法，如用户名和密码、智能卡或证书，增强了网络的准入控制。为了防止中间人攻击和重放攻击，802.11i采用了称为Michael的MIC（Message Integrity Code）技术，用于保护数据包的完整性。此外，预共享密钥（PSK）模式被引入，允许家庭和小型企业用户更方便地设置和管理安全网络。 802.11i标准的实施显著提高了无线网络的安全水平，为用户提供了更加安全的WiFi环境。随着技术的发展，802.11i的很多安全特性已经集成到现代的802.11ac和802.11ax等标准中，继续为无线通信提供强大的安全保障。

IEEE Standard for

Information technology—

Telecommunications and information

exchange between systems—

Local and metropolitan area networks—

Specific requirements

Part 11: Wireless LAN Medium Access Control

(MAC) and Physical Layer (PHY) specifications

Amendment 6: Medium Access Control

(MAC) Security Enhancements

[This amendment is based on IEEE Std 802.11™, 1999 Edition (Reaff 2003), as amended by IEEE Stds

802.11a™-1999, 802.11b™-1999, 802.11b™-1999/Cor 1-2001, 802.11d™-2001, 802.11g™-2003, and

802.11h™-2003.]

NOTE—The editing instructions contained in this amendment define how to merge the material contained herein into

the existing base standard and its amendments to form the comprehensive standard.

The editing instructions are shown in bold italic. Four editing instructions are used: change, delete, insert, and replace.

Change is used to make small corrections in existing text or tables. The editing instruction specifies the location of the

change and describes what is being changed either by using strikethrough

(to remove old material) or underscore (to add

new material). Delete removes existing material. Insert adds new material without disturbing the existing material.

Insertions may require renumbering. If so, renumbering instructions are given in the editing instructions. Replace is used

to make large changes in existing text, subclauses, tables, or figures by removing existing material and replacing it with

new material. Editorial notes will not be carried over into future editions.

1. Overview

1.2 Purpose

Change the fifth bullet of 1.2 as follows:

— Describes the requirements and procedures to provide privacy

confidentiality of user information

being transferred over the wireless medium (WM) and authentication of IEEE 802.11 conformant

devices.

End of changes to Clause 1.

IEEE

Std 802.11i-2004 LOCAL AND METROPOLITAN AREA NETWORKS

2. Normative references

Insert the following references at the appropriate locations in Clause 2:

FIPS PUB 180-1-1995, Secure Hash Standard.

FIPS PUB 197-2001, Advanced Encryption Standard (AES).

IEEE P802.1X™-REV, Draft Standard for Local and Metropolitan Area Networks: Port-Based Network

Access Control.

2, 3, 4

IETF RFC 1321, The MD5 Message-Digest Algorithm, April 1992.

IETF RFC 1750, Randomness Recommendations for Security, December 1994.

IETF RFC 2104, HMAC: Keyed-Hashing for Message Authentication, February 1997.

IETF RFC 2202, Test Cases for HMAC-MD5 and HMAC-SHA-1, September 1997.

IETF RFC 3394, Advanced Encryption Standard (AES) Key Wrap Algorithm, September 2002.

IETF RFC 3610, Counter with CBC-MAC (CCM), September 2003.

IETF RFC 3748, Extensible Authentication Protocol (EAP), March 2004.

End of changes to Clause 2.

3. Definitions

Delete the definition “3.40 privacy.”

Change the definition for “wired equivalent privacy (WEP)” as follows:

3.49 wired equivalent privacy (WEP): The

An optional cryptographic confidentiality algorithm specified

by IEEE 802.11 that may be

used to provide data confidentiality that is subjectively equivalent to the confi-

dentiality of a wired local area network (LAN) medium that does not employ cryptographic techniques to

enhance privacy

confidentiality.

Insert the following definitions in alphabetical order into Clause 3, renumbering as necessary:

3.63 additional authentication data (AAD): Data that are not encrypted, but are cryptographically

protected.

FIPS publications are available from the National Technical Information Service (NTIS), U. S. Dept. of Commerce, 5285 Port Royal

Road, Springfield, VA 22161 (http://www.ntis.org/).

IEEE publications are available from the Institute of Electrical and Electronics Engineers, Inc., 445 Hoes Lane, Piscataway, NJ 08854,

USA (http://standards.ieee.org/).

The IEEE standards or products referred to in this clause are trademarks of the Institute of Electrical and Electronics Engineers, Inc.

This IEEE standards project was not approved by the IEEE-SA Standards Board at the time this publication went to press. For infor-

mation about obtaining a draft, contact the IEEE.

Internet RFCs are available from the Internet Engineering Task Force at http://www.ietf.org/.

IEEE

AMENDMENT 6: MEDIUM ACCESS CONTROL (MAC) SECURITY ENHANCEMENTS Std 802.11i-2004

3.64 authentication, authorization, and accounting (AAA) key: Key information that is jointly negotiated

between the Supplicant and the Authentication Server (AS). This key information is transported via a secure

channel from the AS to the Authenticator. The pairwise master key (PMK) may be derived from the AAA

key.

3.65 authentication and key management (AKM) suite: A set of AKM suite selectors.

3.66 Authentication Server (AS): An entity that provides an authentication service to an Authenticator.

This service determines, from the credentials provided by the Supplicant, whether the Supplicant is autho-

rized to access the services provided by the Authenticator. (IEEE P802.1X-REV

)

3.67 Authenticator: An entity at one end of a point-to-point LAN segment that facilitates authentication of

the entity attached to the other end of that link. (IEEE P802.1X-REV)

3.68 Authenticator address (AA): The IEEE 802.1X Authenticator medium access control (MAC) address.

3.69 authorized: To be explicitly allowed.

3.70 big endian: The concept that, for a given multi-octet numeric representation, the most significant octet

has the lowest address.

3.71 cipher suite: A set of one or more algorithms, designed to provide data confidentiality, data authentic-

ity or integrity, and/or replay protection.

3.72 counter mode (CTR) with CBC-MAC [cipher-block chaining (CBC) with message authentication

code (MAC)] (CCM): A symmetric key block cipher mode providing confidentiality using CTR and data

origin authenticity using CBC-MAC.

NOTE—See IETF RFC 3610.

3.73 decapsulate: To recover an unprotected frame from a protected one.

3.74 decapsulation: The process of generating plaintext data by decapsulating an encapsulated frame.

3.75 EAPOL-Key confirmation key (KCK): A key used to integrity-check an EAPOL-Key frame.

3.76 EAPOL-Key encryption key (KEK): A key used to encrypt the Key Data field in an EAPOL-Key

frame.

3.77 encapsulate: To construct a protected frame from an unprotected frame.

3.78 encapsulation: The process of generating the cryptographic payload from the plaintext data. This com-

prises the cipher text as well as any associated cryptographic state required by the receiver of the data, e.g.,

initialization vectors (IVs), sequence numbers, message integrity codes (MICs), key identifiers.

3.79 4-Way Handshake: A pairwise key management protocol defined by this amendment. It confirms

mutual possession of a pairwise master key (PMK) by two parties and distributes a group temporal key

(GTK).

3.80 group: The entities in a wireless network, e.g., an access point (AP) and its associated stations (STAs),

or all the STAs in an independent basic service set (IBSS) network.

Information on references can be found in Clause 2.

IEEE

Std 802.11i-2004 LOCAL AND METROPOLITAN AREA NETWORKS

3.81 Group Key Handshake: A group key management protocol defined by this amendment. It is used

only to issue a new group temporal key (GTK) to peers with whom the local station (STA) has already

formed security associations.

3.82 group master key (GMK): An auxiliary key that may be used to derive a group temporal key (GTK).

3.83 group temporal key (GTK): A random value, assigned by the broadcast/multicast source, which is

used to protect broadcast/multicast medium access control (MAC) protocol data units (MPDUs) from that

source. The GTK may be derived from a group master key (GMK).

3.84 group temporal key security association (GTKSA): The context resulting from a successful group

temporal key (GTK) distribution exchange via either a Group Key Handshake or a 4-Way Handshake.

3.85 IEEE 802.1X authentication: Extensible Authentication Protocol (EAP) authentication transported by

the IEEE 802.1X protocol.

3.86 key counter: A 256-bit (32-octet) counter that is used in the pseudo-random function (PRF) to generate

initialization vectors (IVs). There is a single key counter per station (STA) that is global to that STA.

3.87 key data encapsulation (KDE): Format for data other than information elements in the EAPOL-Key

Data field.

3.88 key management service: A service to distribute and manage cryptographic keys within a robust secu-

rity network (RSN).

3.89 little endian: The concept that, for a given multi-octet numeric representation, the least significant

octet has the lowest address.

3.90 liveness: A demonstration that the peer is actually participating in this instance of communication.

3.91 message integrity code (MIC): A value generated by a symmetric key cryptographic function. If the

input data are changed, a new value cannot be correctly computed without knowledge of the symmetric key.

Thus, the secret key protects the input data from undetectable alteration. This is traditionally called a

message authentication code (MAC), but the acronym MAC is already reserved for another meaning in this

amendment.

3.92 Michael: The message integrity code (MIC) for the Temporal Key Integrity Protocol (TKIP).

3.93 nonce: A value that shall not be reused with a given key, including over all reinitializations of the sys-

tem through all time.

3.94 pairwise: Two entities that are associated with each other, e.g., an access point (AP) and an associated

station (STA), or a pair of STAs in an independent basic service set (IBSS) network. This term is used to

describe the key hierarchies for keys that are shared only between the two entities in a pairwise association.

3.95 pairwise master key (PMK): The highest order key used within this amendment. The PMK may be

derived from an Extensible Authentication Protocol (EAP) method or may be obtained directly from a pre-

shared key (PSK).

3.96 pairwise master key security association (PMKSA): The context resulting from a successful IEEE

802.1X authentication exchange between the peer and Authentication Server (AS) or from a preshared key

(PSK).

IEEE

AMENDMENT 6: MEDIUM ACCESS CONTROL (MAC) SECURITY ENHANCEMENTS Std 802.11i-2004

3.97 pairwise transient key (PTK): A value that is derived from the pairwise master key (PMK), Authenti-

cator address (AA), Supplicant address (SPA), Anthenticator nonce (ANonce), and Supplicant nonce

(SNonce) using the pseudo-random function (PRF) and that is split up into as many as five keys, i.e., tempo-

ral encryption key, two temporal message integrity code (MIC) keys, EAPOL-Key encryption key (KEK),

EAPOL-Key confirmation key (KCK).

3.98 pairwise transient key security association (PTKSA): The context resulting from a successful

4-Way Handshake exchange between the peer and Authenticator.

3.99 pass-phrase: A secret text string employed to corroborate the user’s identity.

3.100 per-frame encryption key: A unique encryption key constructed for each medium access control

(MAC) protocol data unit (MPDU), employed by some IEEE 802.11 security protocols.

3.101 per-frame sequence counter: For Temporal Key Integrity Protocol (TKIP), the counter that is used

as the nonce in the derivation of the per-frame encryption key. For CCM [counter mode (CTR) with cipher-

block chaining (CBC) with message authentication code (MAC)] Protocol (CCMP), the per-frame initializa-

tion vector (IV).

3.102 pre-robust security network association (pre-RSNA): The type of association used by a pair of sta-

tions (STAs) if the procedure for establishing authentication or association between them did not include the

4-Way Handshake.

3.103 pre-robust security network association (pre-RSNA) equipment: A device that is not able to cre-

ate robust security network associations (RSNAs).

3.104 preshared key (PSK): A static key that is distributed to the units in the system by a method outside

the scope of this amendment, always by some out-of-band means.

3.105 pseudo-random function (PRF): A function that hashes various inputs to derive a pseudo-random

value. To add liveness to the pseudo-random value, a nonce should be one of the inputs.

3.106 robust security network (RSN): A security network that allows only the creation of robust security

network associations (RSNAs). An RSN can be identified by the indication in the RSN Information Element

(IE) of Beacon frames that the group cipher suite specified is not wired equivalent privacy (WEP).

3.107 robust security network association (RSNA): The type of association used by a pair of stations

(STAs) if the procedure to establish authentication or association between them includes the 4-Way Hand-

shake. Note that the existence of a RSNA by a pair of devices does not of itself provide robust security.

Robust security is provided when all devices in the network use RSNAs.

3.108 robust-security-network-association- (RSNA-) capable equipment: A station (STA) that is able to

create RSNAs. Such a device can use pre-RSNAs because of configuration. Notice that RSNA-capable does

not imply full compliance with the RSNA Protocol Implementation Conformance Statement (PICS). A leg-

acy device that has been upgraded to support Temporal Key Integrity Protocol (TKIP) can be RSNA-

capable, but will not be compliant with the PICS if it does not also support CCM [counter mode (CTR) with

cipher-block chaining (CBC) with message authentication code (MAC)] Protocol (CCMP).

3.109 robust-security-network-association- (RSNA-) enabled equipment: A station (STA) when it is

RSNA-capable and dot11RSNAEnabled is set to TRUE.

3.110 robust security network association (RSNA) key management: Key management that includes the

4-Way Handshake, the Group Key Handshake, and the STAKey Handshake.

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