Cryptography
Page 3: Cryptography Overview
Cryptography: Study of mathematical techniques for information security services.
Purpose: Creating secrets.
Cryptanalysis: Study methods to defeat security services.
Purpose: Breaking secrets.
Cryptology: Combined study of cryptography and cryptanalysis.
Page 4: Key Terminology
Plaintext: Original message before encryption.
Ciphertext: Encrypted message that is unreadable to unauthorized users.
Encryption: Process of converting plaintext to ciphertext.
Decryption: Process of converting ciphertext back to plaintext.
Encryption Key: Key used to encrypt plaintext.
Decryption Key: Key used to decrypt ciphertext.
Page 5: Fundamental Goals of Cryptography
Confidentiality: Protection against unauthorized interception.
Integrity: Assurance that data is unaltered without authorization.
Authenticity: Verification of the true source of data.
Non-repudiation: Prevents denial of authorship.
Page 6: Additional Goals of Modern Cryptography
Pseudo-random number generation: Critical for randomness in cryptographic processes.
Anonymity: Protects identities of individuals engaging in transactions.
E-voting: Secure electronic voting systems.
Secret sharing: Distributing a secret among multiple parties.
Zero-knowledge proof: Proving possession of knowledge without revealing it.
Secure multi-party computation: Multiple parties compute a function while keeping their inputs private.
Homomorphic encryption: Computation performed on encrypted data without decryption.
Page 7: Cryptographic Protocols
Enable parties to achieve security goals against adversaries.
Important considerations in protocols:
Identify parties and their context.
Define security goals of the protocol.
Understand capabilities of potential adversaries.
Page 8: Attacker Threat Model
Passive attackers: Only observe, threatening confidentiality.
Active attackers: Can modify or delete messages, threatening confidentiality, integrity, and authenticity.
Kerckhoffs's Principle: The security of a cryptosystem should remain even if everything besides the key is public knowledge.
Shannon’s Maxim: The enemy knows the system—no security through obscurity.
Page 9: Attacker Threat Model – Types of Attacks
Chosen-plaintext attack: Attacker chooses messages to discover corresponding ciphertexts.
Chosen-ciphertext attack: Attacker chooses ciphertexts to reveal corresponding plaintexts.
Attacks may be adaptive, influenced by previous results.
Computationally bounded adversaries: Finite computational resources, cannot utilize quantum computations.
Page 10: Historical Context
Overview of cryptography and cryptanalysis throughout history.
Page 11: Comparing Steganography and Cryptography
Steganography: Hides existence; secrecy relies on the method.
Cryptography: Hides meaning; relies on secrecy of the key, not the method.
Page 12: Caesar Shift Cipher
A simple symmetric substitution cipher using a key (number k).
To Encrypt: Shift letters by k positions.
To Decrypt: Shift letters back by k positions.
Example: SHIFTS with K = 3.
Page 13: Cryptanalysis of Shift Cipher
Brute-force attack: Testing all 25 keys.
Key space needs sufficient size for security—too few keys will weaken encryption.
Page 14: Monoalphabetic Substitution Cipher
Replaces each letter using a permutation.
Key: The specific permutation applied to each letter.
Key space consists of all possible permutations
Example: For English, the space is 26! (about 4 x 10^26).
Page 15: Cryptanalysis of Monoalphabetic Substitution
Dominated cryptography for centuries.
Exhaustive search is infeasible (26! number of keys).
Utilizes frequency analysis.
Page 16: Frequency Analysis
Based on the observation of common letter patterns and combinations in human languages.
Page 17: Cryptanalysis Advantages
Recommendations based on frequency analysis:
Use larger blocks instead of small data bits.
Implement polyalphabetic substitution and stream ciphers to combat frequency analysis.
Page 18: Vigenère Cipher
Improvement on monoalphabetic substitution ciphers.
Uses a key that shifts letters according to a repeating pattern.
Example of encryption process shown with plaintext and ciphertext transformations.
Page 19: Vigenère Cipher Mechanics
A 26x26 table visualizing multiple letters corresponding to ciphertext letters.
Page 20: Cryptanalysis of Vigenère Cipher
Involves examining shifts and periodic nature of the cipher.
Kasisky Test: Identifying key length through repeated patterns.
Page 21: Kasisky Test Application
Examining repeating patterns in the ciphertext to derive potential key length.
Page 22: Vigenère Cracking Techniques
Division of ciphertext and application of frequency analysis based on guessed key length.
Page 23: One-Time Pads and Perfect Secrecy
A modern encryption method resolving vulnerabilities in previous ciphers.
Page 24: One-Time Pad Structure
Involves using long, random keys for encryption equal to the length of the plaintext.
Page 25: Characteristics of One-Time Pad (OTP)
Ensures perfect secrecy; ciphertext gives no information about plaintext.
Page 26: Adversarial Perspective on OTP
Discussing scenarios that might lead to compromising OTP methods.
Page 27: Feasibility of One-Time Pads
Discussion surrounding practical OTP use, key distribution, and security challenges.
Page 28: Cryptanalysis of OTP
Reiterates conditions for OTP integrity and challenges surrounding key usage.
Page 29: Introduction to Modern Symmetric Block Ciphers
Overview of symmetric key cryptography.
Page 30: Symmetric Key Cryptography Basics
Involves algorithms using the same key for both encryption and decryption.
Historic and modern examples provided.
Page 31: Encryption Process Visualization
Illustrated model demonstrating plaintext, encryption, and decryption.
Page 32: Advancements in Block Ciphers
Larger unit transformations enhance security against frequency analysis.
Page 33: Common Symmetric Encryption Algorithms
Lists popular algorithms with respective plaintext and key sizes.
Page 34: DES Overview
Explains Data Encryption Standard and its vulnerabilities over time.
Page 35: AES Overview
Highlights development and characteristics of Advanced Encryption Standard.
Page 36: AES Features
Notable efficiency in software/hardware; showcases resilience against attacks.
Page 37: Speed of Key Search Analysis
Examines average search times for various key sizes and algorithms and their security implications.
Page 38: Block Cipher Modes
Necessity of encryption modes for managing longer messages beyond single blocks.
Page 39: Electronic Code Book (ECB) Mode Analysis
Discusses weaknesses in ECB mode, notably redundancy and predictability.
Page 40: CBC Mode as a Solution
Introduces Cipher Block Chaining with initial vector randomness.
Page 41: Cryptanalysis of CBC Mode
Strategies and best practices for implementing CBC effectively.
Page 42: Complexity of Computational Security
Highlights challenges in achieving perfect security in practice.
Page 43: Introduction to IND-CPA Security Concept
Overview of the security demonstration and property evaluation.
Page 44: IND-CPA Security Conditions
Comparison of classical and modern algorithms' maximal adversarial probabilities of decrypting.
Page 45: Introduction to Public Key Cryptography
Overview of asymmetric cryptography and its unique features compared to symmetric methods.
Page 46: Weaknesses in Symmetric Key Cryptography
Discusses key distribution vulnerabilities and their implications in unsecured online environments.
Page 47: Understanding RSA Cryptography
Discusses RSA's relevance and method of operation.
Page 48: RSA Algorithm Detailed
Illustrates procedures of RSA encryption including prime selection and public key formulation.
Page 49: RSA Encryption and Decryption Process
Explanation of mathematical operations and relations between plaintext and ciphertext.
Page 50: Attacks Against RSA Security
Notes on historical vulnerabilities and future expectations regarding key sizes.
Page 51: Practical Concerns with Key Management
Discusses difficulties associated with securely managing encrypted communications.
Page 52: Digital Signatures and User Authentication
Utilization of cryptographic principles to ensure identity verification in communications.
Page 53: Hash Functions in Cryptography
Overview of cryptographic hash functions, their significance and essential properties.
Page 54: SHA3 and Future of Hashing
Discusses the evolution and competitive selection process for recent cryptographic hashing standards.
Page 55: Public Key Infrastructure (PKI)
Describes roles and functions of certification authorities in establishing secure communications.
Page 56: Certificate Authorities: Functions and Challenges
Overview of trusted CA's roles, their verification processes, and potential issues in trust dynamics.
Page 57: TLS Implementation and Functionality
Discusses the role of TLS in securing communications and its implementation procedures.
Page 58: Certificate Management Processes
Steps needed to acquire and manage valid digital certificates for web security.
Page 59: Certificate Revocation Strategies
Describes mechanisms for certificate revocation and the importance of timely revocation processes.
Page 60: Revocation Challenges and Improvements
Addresses ongoing issues in revocation methods and proposes improvements for efficacy.