密码学应用手册：网络安全的基石

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"《应用密码学手册》是Alfred J. Menezes的作品，该书深入探讨了在信息处理和通信技术迅速发展的时代背景下，密码学的重要性和应用。随着我们进入21世纪，数字信息传输已成为日常生活的核心，涵盖个人交流、金融交易等多个方面。然而，这些基于数字的互动方式也暴露出安全问题，例如数字资产的复制性、隐私保护的挑战以及身份验证的复杂性。本书旨在提供解决这些问题的密码学理论和实践知识。" 在《应用密码学手册》中，作者Alfred J. Menezes深入浅出地讲解了如何利用密码学技术来保障网络安全。随着互联网的普及，我们的个人信息、经济活动越来越依赖于数字通信，这其中包括爱情信件、数字货币和敏感的公司文件等。然而，这些信息是以二进制的形式在网络中传播，对于不熟悉这种语言的普通用户来说，就像无意义的零和一。这就引出了密码学的关键问题：如何确保数字资产的唯一性，如同纸币一样无法轻易复制？如何在卫星通信的环境中实现私密对话，防止信息被窃听？银行如何确信，一笔价值十亿美元的转账请求确实来自比尔·盖茨在斐济的笔记本电脑？书中涵盖了以下几个重要的密码学知识点： 1. **加密算法**：讨论了各种加密方法，如对称加密（如DES、AES）和非对称加密（如RSA、ECC），它们用于保护数据的机密性，防止未经授权的访问。 2. **数字签名**：解释了如何使用公钥和私钥系统进行数字签名，以确保信息的完整性和发送者的身份认证。 3. **散列函数**：介绍散列函数的作用，如MD5和SHA系列，它们可以生成信息的唯一“指纹”，用于检查数据是否被篡改。 4. **认证协议**：探讨了TLS/SSL、SSH等协议，它们确保了网络通信的安全，防止中间人攻击。 5. **密钥管理**：详细讲述了密钥的生成、分发、存储和更新，这是实现安全通信的基础。 6. **密码学与法律政策**：讨论了隐私权、数据保护法以及国际间密码学使用的法规和标准。 7. **安全协议设计**：分析了如何设计和实现安全的网络协议，如电子支付系统和身份验证机制。 8. **密码学最新进展**：涵盖了现代密码学的研究成果，如量子密码学和后量子密码学，以及对未来可能的威胁的预估。通过《应用密码学手册》，读者不仅能了解密码学的基本原理，还能掌握实际应用中的策略和技巧，这对于保护网络空间的安全至关重要，特别是在一个数字化日益加深的世界中。

Chapter

Overview of Cryptography

Contents in Brief

1.1 Introduction ............................. 1

1.2 Information security and cryptography .............. 2

1.3 Background on functions ...................... 6

1.4 Basic terminology and concepts ................... 11

1.5 Symmetric-key encryption ..................... 15

1.6 Digital signatures .......................... 22

1.7 Authentication and identiﬁcation .................. 24

1.8 Public-key cryptography ...................... 25

1.9 Hash functions ........................... 33

1.10 Protocols and mechanisms ..................... 33

1.11 Key establishment, management, and certiﬁcation ......... 35

1.12 Pseudorandom numbers and sequences .............. 39

1.13 Classes of attacks and security models ............... 41

1.14 Notes and further references .................... 45

1.1 Introduction

Cryptographyhas a long and fascinating history. The most complete non-technical account

of the subject is Kahn’s The Codebreakers. This book traces cryptography from its initial

and limited use by the Egyptians some 4000 years ago, to the twentieth century where it

played a crucial role in the outcome of both world wars. Completed in 1963, Kahn’s book

coversthoseaspects of thehistorywhichweremost signiﬁcant(upto that time)to the devel-

opment of the subject. The predominant practitioners of the art were those associated with

the military, the diplomatic service and government in general. Cryptography was used as

a tool to protect national secrets and strategies.

The proliferationof computersand communicationssystems in the 1960s broughtwith

it a demand from the private sector for means to protect information in digital form and to

provide security services. Beginning with the work of Feistel at IBM in the early 1970sand

culminating in 1977 with the adoption as a U.S. Federal Information Processing Standard

for encrypting unclassiﬁed information, DES, the Data Encryption Standard, is the most

well-known cryptographic mechanism in history. It remains the standard means for secur-

ing electronic commerce for many ﬁnancial institutions around the world.

Themoststrikingdevelopmentinthe historyofcryptographycamein1976whenDifﬁe

and Hellman published New Directions in Cryptography. This paper introduced the revolu-

tionary concept of public-key cryptography and also provided a new and ingeniousmethod

2 Ch. 1 Overview of Cryptography

for key exchange, the security of which is based on the intractability of the discrete loga-

rithm problem. Although the authors had no practical realization of a public-key encryp-

tion scheme at the time, the idea was clear and it generated extensive interest and activity

in the cryptographic community. In 1978 Rivest, Shamir, and Adleman discovered the ﬁrst

practical public-key encryption and signature scheme, now referred to as RSA. The RSA

scheme is based on another hard mathematical problem, the intractability of factoring large

integers. This application of a hard mathematical problem to cryptography revitalized ef-

forts to ﬁnd more efﬁcient methods to factor. The 1980s saw major advances in this area

but none which rendered the RSA system insecure. Another class of powerful and practical

public-key schemes was found by ElGamal in 1985. These are also based on the discrete

logarithm problem.

One of the most signiﬁcant contributions provided by public-key cryptography is the

digital signature. In 1991 the ﬁrst international standard for digital signatures (ISO/IEC

9796) was adopted. It is based on the RSA public-key scheme. In 1994 the U.S. Govern-

ment adopted the Digital Signature Standard, a mechanism based on the ElGamal public-

key scheme.

The search for new public-key schemes, improvementsto existing cryptographicmec-

hanisms, and proofs of security continues at a rapid pace. Various standards and infrastruc-

tures involving cryptographyare being put in place. Security products are being developed

to address the security needs of an information intensive society.

The purpose of this book is to give an up-to-date treatise of the principles, techniques,

and algorithms of interest in cryptographic practice. Emphasis has been placed on those

aspects which are most practical and applied. The reader will be made aware of the basic

issues and pointed to speciﬁc related research in the literature where more indepth discus-

sions can be found. Due to the volume of material which is covered, most results will be

stated without proofs. This also serves the purpose of not obscuring the very applied nature

of the subject. This book is intended for both implementers and researchers. It describes

algorithms, systems, and their interactions.

Chapter 1 is a tutorial on the many and various aspects of cryptography. It does not

attempt to convey all of the details and subtleties inherent to the subject. Its purpose is to

introducethe basicissuesandprinciplesand topointthereadertoappropriatechaptersinthe

book for more comprehensive treatments. Speciﬁc techniques are avoided in this chapter.

1.2 Information security and cryptography

The concept of information will be taken to be an understood quantity. To introduce cryp-

tography, an understanding of issues related to information security in general is necessary.

Information security manifests itself in many ways according to the situation and require-

ment. Regardless of who is involved, to one degree or another, all parties to a transaction

must have conﬁdence that certain objectives associated with informationsecurity have been

met. Some of these objectives are listed in Table 1.1.

Over the centuries, an elaborate set of protocols and mechanisms has been created to

deal with information security issues when the information is conveyed by physical doc-

uments. Often the objectives of information security cannot solely be achieved through

mathematical algorithms and protocols alone, but require procedural techniques and abid-

ance of laws to achieve the desired result. For example, privacy of letters is provided by

sealed envelopes delivered by an accepted mail service. The physical security of the en-

velope is, for practical necessity, limited and so laws are enacted which make it a criminal

1997 by CRC Press, Inc. — See accompanying notice at front of chapter.

1.2 Information security and cryptography 3

privacy

or conﬁdentiality

keeping information secret from all but those who are autho-

rized to see it.

data integrity ensuring information has not been altered by unauthorized or

unknown means.

entity authentication

or identiﬁcation

corroboration of the identity of an entity (e.g., a person, a

computer terminal, a credit card, etc.).

message

authentication

corroborating the source of information; also known as data

origin authentication.

signature a means to bind information to an entity.

authorization conveyance, to another entity, of ofﬁcial sanction to do or be

something.

validation a means to provide timeliness of authorization to use or ma-

nipulate information or resources.

access control restricting access to resources to privileged entities.

certiﬁcation endorsement of information by a trusted entity.

timestamping recording the time of creation or existence of information.

witnessing verifying the creation or existence of information by an entity

other than the creator.

receipt acknowledgement that information has been received.

conﬁrmation acknowledgement that services have been provided.

ownership a means to provide an entity with the legal right to use or

transfer a resource to others.

anonymity concealing the identity of an entity involved in some process.

non-repudiation preventing the denial of previous commitments or actions.

revocation retraction of certiﬁcation or authorization.

Table 1.1:

Some information security objectives.

offense to open mail for which one is not authorized. It is sometimes the case that security

is achieved not through the information itself but through the physical document recording

it. For example, paper currency requiresspecial inksand material to prevent counterfeiting.

Conceptually, the way information is recorded has not changed dramatically over time.

Whereas information was typically stored and transmitted on paper, much of it now re-

sides on magnetic media and is transmitted via telecommunications systems, some wire-

less. What has changed dramatically is the ability to copy and alter information. One can

make thousands of identical copies of a piece of information stored electronically and each

is indistinguishable from the original. With information on paper, this is much more difﬁ-

cult. What is needed then for a society where information is mostly stored and transmitted

in electronic form is a means to ensure information security which is independent of the

physical medium recording or conveying it and such that the objectives of information se-

curity rely solely on digital information itself.

One of the fundamental tools used in informationsecurity is the signature. It is a build-

ing block for many other services such as non-repudiation,data origin authentication, iden-

tiﬁcation, and witnessing, to mention a few. Having learned the basics in writing, an indi-

vidual is taught how to produce a handwritten signature for the purpose of identiﬁcation.

At contract age the signature evolves to take on a very integral part of the person’s identity.

This signature is intended to be unique to the individual and serve as a means to identify,

authorize, and validate. With electronic information the concept of a signature needs to be

Handbook of Applied Cryptography by A. Menezes, P. van Oorschot and S. Vanstone.

4 Ch. 1 Overview of Cryptography

redressed; it cannot simply be something unique to the signer and independent of the in-

formation signed. Electronic replication of it is so simple that appending a signature to a

document not signed by the originator of the signature is almost a triviality.

Analogues of the “paper protocols” currently in use are required. Hopefully these new

electronic based protocols are at least as good as those they replace. There is a unique op-

portunity for society to introduce new and more efﬁcient ways of ensuring information se-

curity. Much can be learned fromthe evolutionof the paper based system, mimickingthose

aspects which have served us well and removing the inefﬁciencies.

Achieving information security in an electronic society requires a vast array of techni-

cal and legal skills. There is, however, no guarantee that all of the information security ob-

jectives deemed necessary can be adequately met. The technical means is providedthrough

cryptography.

1.1 Deﬁnition Cryptography is the study of mathematical techniques related to aspects of in-

formation security such as conﬁdentiality, data integrity, entity authentication, and data ori-

gin authentication.

Cryptography is not the only means of providing information security, but rather one set of

techniques.

Cryptographic goals

Of all the information security objectives listed in Table 1.1, the following four form a

frameworkuponwhichtheotherswill be derived: (1) privacyor conﬁdentiality(§1.5,§1.8);

(2) data integrity (§1.9); (3) authentication (§1.7); and (4) non-repudiation (§1.6).

1. Conﬁdentiality is a service used to keep the content of information from all but those

authorized to have it. Secrecy is a term synonymouswith conﬁdentiality and privacy.

There are numerous approaches to providing conﬁdentiality, ranging from physical

protection to mathematical algorithms which render data unintelligible.

2. Data integrity is a service which addresses the unauthorized alteration of data. To

assure data integrity, one must have the ability to detect data manipulation by unau-

thorized parties. Data manipulation includes such things as insertion, deletion, and

substitution.

3. Authenticationis a service related to identiﬁcation. This function appliesto both enti-

ties andinformationitself. Two partiesenteringintoacommunicationshouldidentify

each other. Informationdelivered overa channel should be authenticated as to origin,

date of origin, data content, time sent, etc. For these reasons this aspect of cryptog-

raphy is usually subdivided into two major classes: entity authentication and data

origin authentication. Data origin authentication implicitly provides data integrity

(for if a message is modiﬁed, the source has changed).

4. Non-repudiationis aservice whichpreventsan entityfromdenying previouscommit-

ments or actions. When disputes arise due to an entity denying that certain actions

were taken, a means to resolve the situation is necessary. For example, one entity

may authorize the purchase of property by another entity and later deny such autho-

rization was granted. A procedure involving a trusted third party is needed to resolve

the dispute.

A fundamental goal of cryptography is to adequately address these four areas in both

theory and practice. Cryptography is about the prevention and detection of cheating and

other malicious activities.

This book describes a number of basic cryptographictools (primitives) used to provide

information security. Examples of primitives include encryption schemes (§1.5 and §1.8),

1997 by CRC Press, Inc. — See accompanying notice at front of chapter.

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密码学应用手册：网络安全的基石

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