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.