Unit 6. BASIC CONCEPTS OF CRYPTOLOGY Flashcards
Main Points on Cryptography and Cryptanalysis
Main Points on Cryptography and Cryptanalysis
- Overview of Cryptology
- Cryptology is the study of cryptography (securing information) and cryptanalysis (breaking encryption).
- It involves number theory, algorithms, and formula utilization to protect data.
- Core Cryptographic Terms
- Cryptography: Methods to secure data by altering its form.
- Cryptanalysis: Techniques to break encryption without the key.
- Plaintext & Ciphertext: Unencrypted vs. encrypted data.
- Cipher: The algorithm used to encrypt and decrypt data.
- Encryption & Decryption: The process of encoding and decoding information.
- Key: A secret value used in encryption/decryption.
Types of Cryptosystems
- Symmetric Key Cryptography (SKC): Uses a single key for encryption and decryption (e.g., AES, 3DES).
- Public Key Cryptography (PKC): Uses two keys—a public key for encryption and a private key for decryption (e.g., RSA, ECC).
- Hybrid Cryptography: Combines both SKC for encryption and PKC for secure key exchange.
Types of Cryptosystems
- Symmetric Key Cryptography (SKC): Uses a single key for encryption and decryption (e.g., AES, 3DES).
- Public Key Cryptography (PKC): Uses two keys—a public key for encryption and a private key for decryption (e.g., RSA, ECC).
- Hybrid Cryptography: Combines both SKC for encryption and PKC for secure key exchange.
- Key Security Concepts
- Kerckhoffs’ Principle: A cryptosystem remains secure even if the encryption algorithm is known, as long as the key is kept secret.
- Randomness in Cryptography: Ensures unpredictable key generation to prevent brute-force attacks.
- Key Management: Includes generation, storage, distribution, rotation, and revocation to maintain security.
Key Security Concepts of Cryptography
- Kerckhoffs’ Principle: A cryptosystem remains secure even if the encryption algorithm is known, as long as the key is kept secret.
- Randomness in Cryptography: Ensures unpredictable key generation to prevent brute-force attacks.
- Key Management: Includes generation, storage, distribution, rotation, and revocation to maintain security.
Types of Cryptographic Attacks
Analytic Attacks: Exploit weaknesses in the algorithm (e.g., breaking RSA by factoring primes).
* Implementation Attacks: Target flaws in software/hardware execution.
* Statistical Attacks: Analyze frequency and patterns in encryption.
* Brute-Force Attacks: Try all possible key combinations until the correct one is found.
Cryptanalysis Attack Models
- Ciphertext-Only Attack: Attacker has access only to encrypted data.
- Known-Plaintext Attack: Attacker has both plaintext and its ciphertext, allowing pattern analysis.
- Chosen-Plaintext Attack: Attacker encrypts selected plaintexts to find vulnerabilities.
- Chosen-Ciphertext Attack: Attacker decrypts chosen ciphertexts to discover encryption weaknesses.
Strength of Cryptosystems
A cryptosystem is secure if breaking it is computationally impractical (e.g., requiring billions of years to crack).
* Work factor measures how difficult it is to break encryption.
* Brute-force resistance depends on key length and algorithm complexity.
- Conclusion
- Cryptographic security depends on strong algorithms, proper key management, and protection against attack techniques.
- Future-proof encryption requires continuous advancements in cryptographic techniques and cybersecurity measures.
Main Points on Symmetric Encryption
- Overview of Symmetric Encryption
- Also called: Secret-key encryption or shared-key cryptography.
- Uses one secret key for both encryption and decryption.
- Requires a secure key exchange between parties.
- Used for data at rest (e.g., encrypted files) and real-time data transmission (e.g., secure communications).
Types of Symmetric Encryption Ciphers
- Substitution Ciphers: Replace characters with others (e.g., Caesar cipher).
- Transposition Ciphers: Rearrange the order of characters while keeping the content intact.
Components of Symmetric Encryption
- Algorithm: Defines the encryption process (e.g., AES, DES, RC6).
- Key: A secret value used to transform plaintext into ciphertext.
- Plaintext: The original, readable data before encryption.
- Ciphertext: The encrypted, unreadable output.
Example: Using a Caesar cipher with a shift of 2
* Plaintext: “Dublin”
* Ciphertext: “FWDNKP”
Factors Ensuring Strong Security
- Strong Algorithm: Should resist cryptanalysis even if the encryption method is known.
- Secure Key Management: Protect key generation, storage, and distribution.
- Key Length: Longer keys (128-256 bits) enhance security and resist brute-force attacks.
- Advantages and Disadvantages of Symmetric Encryption
Advantages Disadvantages
Fast & Efficient – Ideal for real-time applications Key Management Complexity – Difficult to manage securely for many users
Strong Security (with proper key size) Security Risk – If the key is compromised, encryption is broken
Automated Key Distribution (via Key Distribution Centers - KDCs) Scalability Issues – Managing multiple keys becomes difficult
Confidentiality Lacks Non-Repudiation – Cannot verify sender identity (asymmetric encryption preferred for this)
Main Points on Asymmetric Encryption and Cryptographic Applications
Overview of Asymmetric Encryption
* Also called Public-Key Cryptography (PKC), uses two keys:
* Public key (used for encryption, shared openly).
* Private key (used for decryption, kept secret).
* Based on mathematical problems like factoring large numbers (RSA) or discrete logarithms (ECC).
* Commonly used in TLS, SSH, PGP, and cryptocurrencies.
Key Components of Asymmetric Encryption
Algorithm: Defines the encryption process (e.g., RSA, ECC, Diffie-Hellman, DSA).
* Key Generation: Generates public-private key pairs.
* Encryption: Uses the public key to encode data.
* Decryption: Uses the private key to decode data.
Advantages & Disadvantages of Asymmetric Encryption
Advantages Disadvantages
Eliminates secure key exchange – No need for pre-shared secret keys Slower than symmetric encryption – Computationally intensive
Scales well – Public keys can be shared with many users Complex key management – Requires secure handling of public/private keys
Ensures authentication & non-repudiation Not ideal for large data volumes – Used mainly for key exchange & signatures
Practical Applications of Cryptography
Authentication & Digital Signatures
* Digital signatures verify authenticity and integrity using asymmetric encryption.
* Used in email security, software verification, and legal documents.
Website Security (HTTPS & TLS)
* Uses public key encryption to establish a secure connection.
* Websites obtain TLS certificates from Certificate Authorities (CAs) (e.g., DigiCert).
* TLS handshake uses asymmetric encryption to exchange session keys, then switches to symmetric encryption (AES) for efficiency.
Email Encryption
* PGP (Pretty Good Privacy) and S/MIME encrypt emails using public-key cryptography.
* ProtonMail provides end-to-end encrypted email services.
Secure Messaging (Social Media Encryption)
* WhatsApp: Uses Signal Protocol (Curve25519 key exchange + AES encryption).
* Telegram: “Secret Chats” use MTProto 2.0 (combining symmetric & asymmetric encryption).
* Signal: Fully open-source encryption with end-to-end security.
Summary of Cryptographic Concepts
Cryptology covers cryptography (securing data) and cryptanalysis (breaking encryption).
* Symmetric encryption is fast & efficient but requires secure key exchange.
* Asymmetric encryption solves key exchange issues but is computationally slower.
* Hybrid encryption combines both for efficiency & security.
* Randomness and key management are critical for strong cryptographic security.
* Cryptographic attacks (e.g., brute force, chosen-plaintext, chosen-ciphertext) must be countered with robust encryption algorithms and long key lengths.
