Foundations of Cryptology Flashcards
Decryption?
Restoring plaintext from ciphertext
plaintext?
Original, non-coded message
Encryption?
Converting plaintext into ciphertext
Ciphertext?
Result of encryption
Cryptosystem?
System for encrypting and decrypting information
Cryptanalysis?
Techniques for deciphering messages without encryption details.
Cryptography?
Study of secure communication techniques.
Cryptology?
Encompasses both cryptography and cryptanalysis
Generic Encryption Notation?
c = Ek(m); m = Dkı(c)
Caesar Cipher?
-Overview: Early substitution cipher used by Julius Caesar. mono-alphabetic
-Mechanism: Shifts each letter three places to the left.
-Vulnerability: Susceptible to frequency analysis due to its simplicity.
Vigenère Cipher?
-Overview: Polyalphabetic substitution cipher developed by Blaise de Vigenère.
-Mechanism: Uses a repeating keyword to shift letters.
-Strength: Multiple ciphertext letters for each plaintext letter.
-Weakness: Vulnerable to cryptanalysis due to shared frequency distribution a
statistical technique can be applied.
One-Time Pads?
Overview: Perfect encryption scheme, invented by Gilbert Vernam.
Mechanism: Uses a pad of random values and the XOR operation.
Requirements: The pad must be used only once, as long as the message, is securely distributed, and truly random.
Practicality: Impractical due to cumbersome key management and distribution.
Steganography?
Definition: Hiding data within another media type to conceal its existence.
Methods: Character marking, invisible ink, typewriter correction ribbon, least significant bit alterations in images.
Usage: Information theft, digital watermarks for intellectual property protection.
Nonce?
Definition: A random number used once in a cryptographic function.
Purpose: Adds randomness to the encryption process to strengthen it.
Initialization Vector (IV)?
Definition: Random values used with algorithms to prevent pattern creation during encryption.
Usage: Ensures identical plaintext values do not produce the same ciphertext when encrypted with the same key.
Zero-Knowledge Proof?
Definition: Proving knowledge of a fact to a third party without revealing the fact itself.
Example: Proving knowledge of a password without disclosing it.
Split Knowledge?
Definition: Dividing information or privilege among multiple users to prevent any single person from compromising security.
Example: Key escrow, where a secret key is held by a third party until certain conditions are met.
Goals of Cryptography?
-Confidentiality: Ensuring that information is not accessible to unauthorized individuals.
-Integrity: Ensuring that information is accurate and complete.
-Authentication: Verifying the identity of individuals and entities.
-Non-repudiation: Preventing individuals from denying their actions.
Key
Definition: A piece of information, usually a string of numbers or letters, used in cryptographic algorithms to encode or decode data.
Types: Can vary in size and form based on the cryptographic method.
Security: The strength of encryption depends on the security of the key, influenced by:
The algorithm used.
The size of the key.
How the key is generated.
The key exchange process
Three Dimensions of Cryptographic
Systems?
1-the type of operation used for encryption.
2-number of keys used
3-the way the plaintext is processed
The Kerckhoff Principle
Principle: The security of a cryptosystem should rely on the secrecy of the key, not the algorithm.
Ciphers?
Monoalphabetic Cipher: Substitution cipher using a fixed key.
Polyalphabetic Cipher: Uses multiple substitution alphabets to improve security.
Running Key Cipher: Uses a key based on a book or document.
Concealment Cipher: Hides the message within another message.
Block Cipher
Stream Cipher
Types of Operations in Ciphers?
Transposition: Rearranges letters of plaintext.
Substitution: Replaces each character or bit of plaintext with a different character.
Other Techniques Used in Ciphers?
Compression: Reduces redundancy before encryption.
Expansion: Increases plaintext size to match key sizes.
Padding: Adds material to the plaintext before encryption.
Key Mixing: Uses subkeys to limit key exposure.
Two Attributes of Ciphers?
Confusion: Complicates the relationship between plaintext and key, achieved by substitution.
Diffusion: Spreads changes in plaintext throughout ciphertext, achieved by transposition.
