Cryptography Quiz

Cryptography is the practice and study of techniques for secure communication in the presence of adversarial behavior.

Modern cryptography exists at the intersection of mathematics, computer science, information security, electrical engineering, digital signal processing, physics, and other disciplines.

Core concepts related to information security (data confidentiality, data integrity, authentication, and non-repudiation) are also central to cryptography.

Practical applications of cryptography include electronic commerce, chip-based payment cards, digital currencies, computer passwords, and military communications.

Cryptography prior to the modern age was effectively synonymous with encryption, converting readable information (plaintext) to unintelligible nonsense text (ciphertext), which can only be read by reversing the process (decryption).

Modern cryptography is heavily based on mathematical theory and computer science practice; cryptographic algorithms are designed around computational hardness assumptions, making such algorithms hard to break in actual practice by any adversary.

The growth of cryptographic technology has raised a number of legal issues in the Information Age.

There are two main types of cryptosystems: symmetric and asymmetric.

Breaking a message without using frequency analysis essentially required knowledge of the cipher used and perhaps of the key involved, thus making espionage, bribery, burglary, defection, etc., more attractive approaches to the cryptanalytically uninformed.

Different physical devices and aids have been used to assist with ciphers.

Many mechanical encryption/decryption devices were invented early in the 20th century, and several patented, among them rotor machines—famously including the Enigma machine used by the German government and military from the late 1920s and during World War II.

Language letter frequencies may offer little help for some extended historical encryption techniques such as homophonic cipher that tend to flatten the frequency distribution.Cryptography: A Brief History and Overview

• Cryptography was used in ancient times to protect messages from being read by unauthorized persons.

• Cryptanalysis was made more efficient during WWII by the development of the Colossus, the world's first fully electronic, digital, programmable computer, which assisted in decryption of ciphers generated by the German Army's Lorenz SZ40/42 machine.

• Cryptography began to be extensively researched in the mid-1970s, leading to the development of the Data Encryption Standard (DES) algorithm and the Diffie-Hellman key exchange algorithm.

• Modern cryptography makes extensive use of mathematical subdisciplines, including information theory, computational complexity, statistics, combinatorics, abstract algebra, number theory, and finite mathematics.

• Symmetric-key cryptography refers to encryption methods in which both the sender and receiver share the same key.

• Block ciphers and stream ciphers are two implementations of symmetric-key ciphers.

• Public-key cryptography uses two different but mathematically related keys--a public key and a private key--for encryption and decryption of a message.

• Public-key algorithms are most often based on the computational complexity of "hard" problems, often from number theory.

• Cryptographic hash functions are cryptographic algorithms that generate and use keys to encrypt data.

• Cryptographic hash functions take a message of any length as input, and output a short, fixed-length hash, which can be used in a digital signature.

• MD4 and MD5 are widely used but broken hash functions, while SHA-1 and SHA-2 are more secure.

• Cryptography is an important tool in computer security, but designers must consider probable future developments in technology and cryptography.Cryptography: its uses, applications, and legal issues

• Cryptography is the practice of secure communication in the presence of third parties. It is used to verify the authenticity of data retrieved from an untrusted source or to add a layer of security.

• The goal of cryptanalysis is to find some weakness or insecurity in a cryptographic scheme, thus permitting its subversion or evasion.

• Most ciphers, apart from the one-time pad, can be broken with enough computational effort by brute force attack, but the amount of effort needed may be exponentially dependent on the key size.

• There are a wide variety of cryptanalytic attacks, and they can be classified in any of several ways.

• Cryptanalysis of symmetric-key ciphers typically involves looking for attacks against the block ciphers or stream ciphers that are more efficient than any attack that could be against a perfect cipher.

• Public-key algorithms are based on the computational difficulty of various problems. The most famous of these are the difficulty of integer factorization of semiprimes and the difficulty of calculating discrete logarithms.

• Lightweight cryptography (LWC) concerns cryptographic algorithms developed for a strictly constrained environment.

• Cryptography is widely used on the internet to help protect user-data and prevent eavesdropping.

• Cryptographic techniques enable cryptocurrency technologies, such as distributed ledger technologies (e.g., blockchains), which finance cryptoeconomics applications such as decentralized finance (DeFi).

• Cryptography has long been of interest to intelligence gathering and law enforcement agencies. In some countries, even the domestic use of cryptography is, or has been, restricted.

• In the 1990s, there were several challenges to US export regulation of cryptography.

• Another contentious issue connected to cryptography in the United States is the influence of the National Security Agency on cipher development and policy.Cryptography and government policy

• The NSA and cryptography

• The Clipper chip affair

• Digital rights management

• Forced disclosure of encryption keys

• United States v. Fricosu

• FBI-Apple encryption dispute

• Plausible deniability in cryptography