Everyday Cryptography · Fundamental Principles and Applications by Martin, Keith -- Read -- Imperial Library of Trantor

Index

Title page Copyright Contents Preface to the Second Edition Preface List of Figures List of Tables Part I Setting the Scene 1 Basic Principles

1.1 Why information security?

1.1.1 The rising profile of information security 1.1.2 Two very different office environments

An Old Office A Modern Office

1.1.3 Differing perspectives

Individual Perspective Business Perspective Government Perspective

1.1.4 The importance of security infrastructure

1.2 Security risks

1.2.1 Types of attack

Passive Attacks Active Attacks

1.2.2 Security risks for a simple scenario 1.2.3 Choosing security mechanisms

1.3 Security services

1.3.1 Basic definitions 1.3.2 Relationships between security services

Data Origin Authentication is a Stronger Notion than Data Integrity Non-Repudiation of a Source is a Stronger Notion than Data Origin Authentication Data Origin Authentication and Entity Authentication are Different Data Origin Authentication Plus a Freshness Check can Provide Entity Authentication Confidentiality Does Not Imply Data Origin Authentication

1.4 Fundamentals of cryptosystems

1.4.1 Different cryptographic concepts 1.4.2 Cryptographic primitives for security services 1.4.3 Basic model of a cryptosystem 1.4.4 Codes 1.4.5 Steganography 1.4.6 Access control 1.4.7 Two types of cryptosystem 1.4.8 Secrecy of the encryption key

1.5 Cryptosystem security assumptions

1.5.1 Standard assumptions 1.5.2 Theoretical attack models 1.5.3 Knowledge of the encryption algorithm

The Impact of Kerckhoffs’ Second Principle The Case for Publicly Known Algorithms What Happens in Practice?

1.5.4 Use of publicly known algorithms

1.6 Breaking cryptosystems

1.6.1 Some useful preliminaries

Binary Numbers XOR Exponentiation Concatenation

1.6.2 Key lengths and keyspaces 1.6.3 Breaking encryption algorithms 1.6.4 Exhaustive key searches

Conducting an Exhaustive Key Search Identifying Candidate Decryption Keys Determining the Correct Decryption Key Protecting Against Exhaustive Key Searches

1.6.5 Classes of attack 1.6.6 Academic attacks

1.7 Summary 1.8 Further reading 1.9 Activities

2 Historical Cryptosystems

2.1 Monoalphabetic ciphers

2.1.1 Caesar Cipher

Description of the Caesar Cipher Fitting the Caesar Cipher to the Basic Model Mathematical Description of the Caesar Cipher Insecurity of the Caesar Cipher

2.1.2 Simple Substitution Cipher

Permutations Description of the Simple Substitution Cipher Fitting the Simple Substitution Cipher to the Basic Model Keyspace of the Simple Substitution Cipher Insecurity of the Simple Substitution Cipher

2.1.3 Frequency analysis

The Nature of Plaintexts Letter Frequency Analysis Limitations of Letter Frequency Analysis Sufficiency of Keyspace Size

2.1.4 A study of theory versus practice

Theory: Uniqueness of the Plaintext Practice: Statistical Information The Gap Between Theory and Practice

2.2 Historical advances

2.2.1 Design improvements 2.2.2 Playfair Cipher

Preprocessing for the Playfair Cipher Encryption Using the Playfair Cipher Example of a Playfair Cipher Cryptanalysis of the Playfair Cipher Lessons from the Playfair Cipher

2.2.3 Homophonic encoding

Example of Homophonic Encoding Single Letter Frequency Analysis of Homophonic Encoding Problems with Homophonic Encoding Lesson from Homophonic Encoding

2.2.4 Vigenère Cipher

Encryption Using the Vigenère Cipher Cryptanalysis of the Vigenère Cipher Lesson from the Vigenère Cipher

2.3 Summary 2.4 Further reading 2.5 Activities

3 Theoretical versus Practical Security

3.1 Theoretical security

3.1.1 Perfect secrecy

Motivating Perfect Secrecy Defining Perfect Secrecy

3.1.2 A simple cryptosystem offering perfect secrecy

Description of the Cryptosystem The Attacker’s View Comments on the Simple Cryptosystem

3.1.3 One-time pads

Properties of a One-Time Pad One-Time Pad from the Vigenère Cipher Consequences of Key Reuse in a One-Time Pad One-Time Pad from a Latin Square Vernam Cipher

3.1.4 Theoretical security summary

3.2 Practical security

3.2.1 One-time pad in practice

Key Management Issues with a One-Time Pad One-Time Pads in Practice

3.2.2 Cover time 3.2.3 Computational complexity

Complexity of Simple Processes Polynomial and Exponential Time Computing Real Attack Times Limitations of Complexity

3.2.4 Design process of a cryptosystem

Selection or Design of a Primitive Mode of Use Implementation Key Management

3.2.5 Evaluating security

Assessing the Security of a Cryptographic Algorithm Assessing the Security of a Cryptographic Protocol Assessing the Security of a Cryptosystem

3.2.6 Adequate security 3.2.7 Towards a notion of practical security

3.3 Summary 3.4 Further reading 3.5 Activities

Part II The Cryptographic Toolkit 4 Symmetric Encryption

4.1 Classification of symmetric encryption algorithms 4.2 Stream ciphers

4.2.1 Model of a stream cipher 4.2.2 Key management of stream ciphers 4.2.3 The impact of errors 4.2.4 Properties of stream ciphers 4.2.5 Examples of stream ciphers

4.3 Block ciphers

4.3.1 Model of a block cipher 4.3.2 Properties of block ciphers 4.3.3 Block cipher algorithms

4.4 The Data Encryption Standard

4.4.1 Feistel Cipher

Encryption Using a Feistel Cipher Choosing the Round Function Decryption Using a Feistel Cipher Number of Rounds

4.4.2 Specification of DES 4.4.3 Brief history of DES

Milestones in the History of DES Early Design Criticisms DES Key Searches

4.4.4 Triple DES

3-Key Triple DES 2-Key Triple DES Triple DES in Practice

4.5 The Advanced Encryption Standard

4.5.1 Development of AES 4.5.2 Design of AES

AES Encryption AES Decryption

4.5.3 AES today

4.6 Modes of operation

4.6.1 Electronic Code Book mode

How ECB Mode Works Problems with ECB Mode

4.6.2 Cipher Block Chaining mode

Encryption Using CBC Mode Decryption Using CBC Mode Impact of Transmission Errors in CBC Mode Properties of CBC Mode

4.6.3 Cipher Feedback mode

Encryption Using CFB Mode Decryption Using CFB Mode Reduced Feedback CFB Mode Properties of CFB Mode

4.6.4 Counter mode

Encryption and Decryption Using CTR Mode Properties of CTR Mode

4.6.5 Comparing modes of operation

4.7 Use of symmetric encryption

4.7.1 Other types of symmetric encryption 4.7.2 The future for symmetric encryption

4.8 Summary 4.9 Further reading 4.10 Activities

5 Public-Key Encryption

5.1 Public-key cryptography

5.1.1 Motivation for public-key cryptography

Problems with Symmetric Cryptography History of Public-Key Cryptography

5.1.2 Properties of public-key cryptosystems

The Briefcase Protocol A Blueprint for a Public-Key Cryptosystem A Better Briefcase Analogy?

5.1.3 Some mathematical preliminaries

Primes Modular Arithmetic Some Notation

5.1.4 One-way functions for public-key cryptography

Trapdoor One-Way Functions Multiplication of Two Large Primes Modular Exponentiation with a Large Modulus Non-Modular Exponentiation

5.2 RSA

5.2.1 Setting up RSA

Generating an RSA Key Pair

5.2.2 Encryption and decryption using RSA

RSA Encryption RSA Decryption

5.2.3 Security of RSA

Decrypting a Ciphertext Without Knowledge of the Private Key Determining the Private Key Directly from the Public Key Specific Instance Attacks on RSA RSA Security Summary

5.2.4 RSA in practice

Probabilistic Encryption RSA-OAEP

5.3 ElGamal and elliptic curve variants

5.3.1 Setting up ElGamal 5.3.2 Encryption and decryption using ElGamal

Elgamal Encryption Elgamal Decryption

5.3.3 Security of ElGamal

Decrypting a Ciphertext Without Knowledge of the Private Key Determining the Private Key Directly from the Public Key Elgamal Security Summary

5.3.4 ElGamal in practice

Use of System-Wide Parameters Probabilistic Encryption Message Expansion

5.3.5 Elliptic Curve Cryptography

5.4 Comparison of RSA, ElGamal, and ECC

5.4.1 Popularity of RSA 5.4.2 Performance issues 5.4.3 Security issues

Key Lengths of Public-Key Cryptosystems Comparing Security of Public-Key Cryptosystems Exhaustive Key Searches for Private Keys Relative Key Lengths

5.5 Use of public-key encryption

5.5.1 Limiting factors 5.5.2 Hybrid encryption 5.5.3 Other types of public-key cryptosystem 5.5.4 The future for public-key cryptosystems

5.6 Summary 5.7 Further reading 5.8 Activities

6 Data Integrity

6.1 Different levels of data integrity 6.2 Hash functions

6.2.1 Properties of a hash function

Practical Property 1: Compresses Arbitrary Long Inputs into a Fixed Length Output Practical Property 2: Easy to Compute Security Property 1: Preimage Resistance Security Property 2: Second Preimage Resistance Security Property 3: Collision Resistance Relationships Between the Three Security Properties

6.2.2 Applications of hash functions

Application Requiring Preimage Resistance Application Requiring Second Preimage Resistance Application Requiring Collision Resistance

6.2.3 Attacking hash functions in theory

The Dangers of a Very Small Hash The Dangers of a Small Hash Birthday Attacks

6.2.4 Hash functions in practice

Hash Function Design A Brief History of Modern Hash Functions

6.2.5 SHA-3

SHA-3 Design SHA-3 Family Use of SHA-3

6.3 Message authentication codes

6.3.1 Does symmetric encryption provide data origin authentication? 6.3.2 MAC properties 6.3.3 CBC-MAC

Computing CBC-MAC Checking CBC-MAC Security of CBC-MAC CBC-MAC in Practice

6.3.4 HMAC 6.3.5 MACs and non-repudiation 6.3.6 Using MACs with encryption

Using Separate Primitives Authenticated-Encryption Primitives Galois Counter Mode Other Authenticated-Encryption Modes

6.4 Summary 6.5 Further reading 6.6 Activities

7 Digital Signature Schemes

7.1 Digital signatures

7.1.1 The basic idea 7.1.2 Electronic signatures 7.1.3 Digital signature scheme fundamentals

Requirements for a Digital Signature Scheme Basic Properties of a Digital Signature Scheme

7.2 Non-repudiation using symmetric techniques

7.2.1 Arbitrated digital signature schemes 7.2.2 Asymmetric trust relationships 7.2.3 Enforced trust

7.3 Digital signature schemes based on RSA

7.3.1 Complementary requirements 7.3.2 Basic model of a digital signature scheme 7.3.3 Two different approaches 7.3.4 RSA digital signature scheme with appendix

The Signing Process The Verification Process Reasons for Hashing RSA is Special

7.3.5 RSA digital signature scheme with message recovery

Advantages of Digital Signature Schemes with Message Recovery Signing and Verifying Using a Digital Signature Scheme with Message Recovery Redundancy Techniques Digital Signature Schemes with Message Recovery and Confidentiality

7.3.6 Other digital signature schemes

7.4 Digital signature schemes in practice

7.4.1 Security of digital signature schemes

Security of the Signature Key Security of the Verification Key Security of the Hash Function

7.4.2 Using digital signature schemes with encryption 7.4.3 Relationship with handwritten signatures

Environmental Differences Security Differences Practical Differences Flexibility Differences

7.4.4 Relationship with advanced electronic signatures

7.5 Summary 7.6 Further reading 7.7 Activities

8 Entity Authentication

8.1 Random number generation

8.1.1 The need for randomness 8.1.2 What is randomness? 8.1.3 Non-deterministic generators

Hardware-Based Non-Deterministic Generators Software-Based Non-Deterministic Generators Non-Deterministic Generators in Practice

8.1.4 Deterministic generators

Basic Model of a Deterministic Generator Deterministic Generators in Practice

8.2 Providing freshness

8.2.1 Clock-based mechanisms 8.2.2 Sequence numbers 8.2.3 Nonce-based mechanisms 8.2.4 Comparison of freshness mechanisms

8.3 Fundamentals of entity authentication

8.3.1 A problem with entity authentication 8.3.2 Applications of entity authentication 8.3.3 General categories of identification information

Something the Claimant Has Something the Claimant Is Something the Claimant Knows

8.4 Passwords

8.4.1 Problems with passwords 8.4.2 Cryptographic password protection

Traditional Approach to Unix Password Protection Key Stretching

8.5 Dynamic password schemes

8.5.1 Idea behind dynamic password schemes 8.5.2 Example dynamic password scheme

Dynamic Password Scheme Description Analysis of Dynamic Password Scheme Dynamic Password Schemes in Practice

8.6 Zero-knowledge mechanisms

8.6.1 Motivation for zero-knowledge 8.6.2 Zero-knowledge analogy 8.6.3 Zero-knowledge in practice

8.7 Summary 8.8 Further reading 8.9 Activities

9 Cryptographic Protocols

9.1 Protocol basics

9.1.1 Operational motivation for protocols 9.1.2 Environmental motivation for protocols 9.1.3 Components of a cryptographic protocol

9.2 From objectives to a protocol

9.2.1 Stages of protocol design 9.2.2 Challenges of the stages of protocol design

Defining the Objectives Determining the Protocol Goals Specifying the Protocol Standards for Cryptographic Protocols

9.2.3 Assumptions and actions

Assumptions Actions

9.2.4 The wider protocol design process

9.3 Analysing a simple protocol

9.3.1 A simple application

The Objectives The Protocol Goals Candidate Protocols

9.3.2 Protocol 1