Data Security - Cryptography Lecture Notes

Flashcards covering the fundamentals of cryptography, historical and modern ciphers (DES, AES, RSA), and security mechanisms like PKI, hashing, and digital signatures based on CIT2371 lecture notes.

Cryptography

A technique of securing information and communications through the use of codes so that only intended persons can understand and process it, derived from the prefix "crypt" (hidden) and suffix "graphy" (writing).

Algorithms

A set of rule-based calculations obtained from mathematical concepts used to convert messages in ways that make it hard to decode them.

Cryptanalysis

The science of analyzing and breaking secure communication, involving analytical reasoning, mathematical tools, and pattern finding.

Cryptology

An academic field that embraces both the practice of cryptography and the science of cryptanalysis.

Encryption

The process of converting messages or data into a form that cannot be read without decrypting or deciphering it, originating from the Greek word "kryptos" meaning hidden or secret.

LUCIFER

A computerized cryptosystem developed by Horst Feistel at IBM in the early 1970s that utilized both substitution and transposition.

Data Encryption Standard (DES)

A 1977 NIST cryptographic technique based on LUCIFER that transformed 64-bit segments of information using a 56-bit key; it was broken in 1998.

RSA System

A system created in 1978 by Ronald L. Rivest, Adi Shamir, and Leonard Adleman that uses the formula $n = pq$ to capitalize on the difficulty of factoring large prime numbers.

Advanced Encryption Standard (AES)

A fast block cipher that replaced DES as an official U.S. government standard in 2002, supporting key lengths and block sizes of 128, 192, or 256 bits.

International Data Encryption Algorithm (IDEA)

An encryption system based on 128-bit segments developed by the Swiss Federal Institute of Technology in the 1990s.

Symmetric Encryption

A type of cryptography where a single secret key is shared by both the sender and recipient to both encrypt and decrypt a message.

Asymmetric Encryption

Also called public key encryption, it uses a pair of mathematically related keys: a public key for encryption and a private key for decryption.

Plaintext

The original message or data input before it undergoes the encryption process.

Ciphertext

The encrypted form of a message that results from applying an encryption algorithm and a key to plaintext.

Substitutions

A cryptosystem operation where each element of the plaintext, such as a bit or letter, is mapped to another element.

Transpositions

A cryptosystem operation where the elements of the plaintext are re-arranged.

Brute Force Attack

An attack that involves trying every possible key until the correct translation of encrypted text into plaintext is obtained.

Block Cipher

A cipher where a fixed-sized block of elements is transformed into an output block in one go, usually in multiples of 64 bits.

Stream Cipher

A cipher that processes input elements continuously one at a time by mathematically combining data with a generated keystream.

Feistel Cipher

A block cipher scheme where input is broken into left (L) and right (R) blocks, cycled through a function (f), XORed, and swapped repeatedly.

SubBytes

A non-linear substitution step in the AES algorithm where each byte in a state is replaced with another according to a lookup table.

ShiftRows

A transposition step in the AES algorithm where each row of the 4 by 4 array is shifted cyclically by a certain number of steps.

MixColumns

An AES operation that combines the four bytes in each column of the state to provide mixing.

AddRoundKey

An AES step where each byte of the state is combined with a round key using a bitwise XOR operation.

Hash Function

A mathematical function used to ensure integrity by converting variably-sized data into a small, fixed-length datum.

SHA-1 (Secure Hash Algorithm)

A hash algorithm that takes an input of less than $2^{64}$ bits and produces a 160-bit message digest.

Public Key Infrastructure (PKI)

A security architecture used to create a secure data infrastructure and provide proof of content and authentication over insecure networks like the Internet.

Digital Signature

A unique, encrypted numerical value generated by a hashing algorithm and a private key, used to prove ownership and verify that data has not been edited.

Certificate Authority (CA)

The entity responsible for issuing and validating public key certificates.

Computationally Secure

An encryption scheme property where the cost of breaking it exceeds the value of the information or the time required exceeds the information's lifetime.