Q: What is Access Control?

A: Ensures that resources are only granted to those users who are entitled to them.

Q: What is Encryption?

A: The process of converting plaintext data into an unreadable format (ciphertext) to prevent unauthorized access.

Q: What is Decryption?

A: The process of converting ciphertext back into its original format (plaintext).

Q: What is a Key in cryptography?

A: Information used in the cipher, known only to the sender/receiver.

Q: What is Authentication?

A: The process of verifying the identity of a user, device, or system.

Q: What is a Threat in computer security?

A: An action or event that might compromise security.

Q: What are some basic problems and concerns involving cryptographic systems?

A: Weak encryption, improper key management, inadequate randomness, inadequate authentication.

Q: What is Plaintext?

A: The original, readable message that is input into the encryption process.

Q: What is Ciphertext?

A: The scrambled, unreadable message that results from the encryption process.

Q: What is a Cipher?

A: The algorithm used for transforming plaintext to ciphertext.

Q: What are the pros of classical cryptographic techniques?

A: Simple, can be done manually, protect plaintext from casual snooping.

Q: What are the cons of classical cryptographic techniques?

A: Limited security, vulnerable to frequency analysis and brute-force attacks, challenging key management.

Q: How does the Caesar Cipher work?

A: By shifting the letters in the plaintext message by a certain number of positions, known as the “shift” or “key”.

Q: What is Symmetric Encryption?

A: A form of cryptosystem in which encryption and decryption are performed using the same key.

Q: Compare Symmetric and Asymmetric Cryptography.

A: Symmetric uses a single key for encryption and decryption; asymmetric uses a pair of keys (public and private).

Q: What are Hash Functions?

A: Algorithms that calculate a fixed length hash value from plaintext, making it impossible to recover the contents of the plaintext.

Q: What was the first recorded use of cryptography for correspondence?

A: The Spartans' use of the scytale.

Q: What is the Enigma machine?

A: A cipher device used extensively by Nazi Germany during World War II to protect communication.

Q: What is the Hebern cipher machine?

A: A typewriter-like device with 26 letters that light up, scrambling the electrical signal between the letters of the keyboard and the light panel.

Q: What can lead to a break in good encryption schemes?

A: Using weak algorithms, improper key management, using vulnerable algorithms, and incorrect implementation of strong algorithms.

Q: What is divisibility in mathematics?

A: If a and b are integers, with a ≠ 0, a divides b if there exists an integer q such that b = a q.

Q: What is Modular Arithmetic?

A: A system of arithmetic for integers, where numbers wrap around upon reaching a certain value, called the modulus.

Q: How do you apply the Euclidean Algorithm to find the GCD?

A: Using repeated division: GCD (A,B) = GCD (B,R), where R is the remainder when A is divided by B.

Q: What is a Prime Number?

A: A natural number greater than 1 that has no positive divisors other than 1 and itself.

Q: What is Euler’s Totient Function?

A: The number of positive integers less than or equal to a given integer that are relatively prime to it.

Q: What are Stream Ciphers?

A: They encrypt plaintext one bit or byte at a time, suitable for varying data lengths and fast encryption/decryption.

Q: What are Block Ciphers?

A: They encrypt data in fixed-size blocks, suitable for applications that manage blocks of data, with higher processing overhead.

Q: Why is a Feistel cipher superior to a full permutation block cipher?

A: It is guaranteed to be invertible, allowing for secure decryption, and has similar encryption and decryption operations.

Q: What are the parts of a Feistel cipher that give it security?

A: Round function, invertibility, and key schedule.

Q: How does the Data Encryption Standard (DES) work?

A: Through initial permutation, 16 rounds of processing, and a final permutation, incorporating substitution and transposition.

Q: What is the Advanced Encryption Standard (AES)?

A: A block cipher that encrypts data in 128-bit blocks using key lengths of 128, 192, or 256 bits.

Q: What is Electronic Code Book (ECB) mode?

A: A block cipher mode that directly encrypts each block of input plaintext into blocks of encrypted ciphertext.

Q: What is Cipher Block Chaining (CBC) mode?

A: An advancement on ECB where the previous cipher block is XORed with the next plaintext block before encryption.

Q: What is a meet-in-the-middle attack?

A: A cryptanalytic attack that divides the key space into two parts and encrypts plaintext while decrypting ciphertext to find a match.

Q: What is the difference between TRNGs, PRNGs, and CSPRNGs?

A: TRNGs generate numbers from physical processes, PRNGs use deterministic algorithms, and CSPRNGs are secure PRNGs suitable for cryptography.

Q: What is Symmetric Key Encryption?

A: It uses the same key for both encryption and decryption.

Q: What is Public Key Encryption?

A: It uses a pair of keys, a public key and a private key, for encryption and decryption.

Q: How does RSA encryption work?

A: One party generates a key pair, uses the public key for encryption, and the private key for decryption.

Q: How does Diffie-Hellman key exchange work?

A: Both parties exchange public key information to arrive at a shared secret key.

Q: What is Elliptic Curve Cryptography (ECC)?

A: A public-key cryptography approach based on the algebraic structure of elliptic curves over finite fields.

Q: What are hash functions used for?

A: To ensure data integrity, generate checksums, and create secure hash algorithms in cryptographic applications.

Q: What is a cryptographic hash function?

A: A transformation that takes an input and returns a fixed-size string of bytes unique to each unique input.

Q: What properties should a good cryptographic hash function have?

A: Preimage resistance, second preimage resistance, and collision resistance.

Q: What is a hash function collision?

A: When two different inputs result in the same output.

Q: What are some good hashing algorithms?

A: SHA-256 and SHA-3.

Q: What is a Message Authentication Code (MAC)?

A: A code used to authenticate the origin and integrity of a message.

Q: What are Digital Signatures?

A: Digital signatures ensure the authenticity and integrity of a message, software, or digital document.

Q: How do you verify a digital signature?

A: By decrypting the signature with the sender's public key and comparing it to the hash of the received message.

Q: What is Public Key Infrastructure (PKI)?

A: A system for the creation, storage, distribution, and revocation of digital certificates.

Q: What is a Certificate Authority (CA)?

A: An entity that issues digital certificates for use by other parties.

Q: How are keys managed in cryptographic systems?

A: Through generation, distribution, storage, and destruction, with secure protocols.

Q: What is a Bitcoin block?

A: A file where data related to transactions are permanently recorded.

Q: What sets a limit on the size of the Bitcoin block?

A: Blocksize.

Q: What is included in the Block Header of a Bitcoin block?

A: Version, Previous Block Hash, Merkle Root, Timestamp, Difficulty Target, Nonce, and Transaction Counter.

Q: What is the Previous Block Hash?

A: An encrypted number of the previous block’s header.

Q: What is the Merkle Root?

A: An encrypted number of transactions in the Merkle tree of the current block.

Q: What does the Timestamp in a Bitcoin block signify?

A: It places the block in the blockchain.

Q: What is the Difficulty Target in a Bitcoin block?

A: The difficulty rating of the target encrypted number, signifying the difficulty in generating an encrypted number that is equal to or less than the target.

Q: What is the Nonce in a Bitcoin block?

A: A number that the miner increases incrementally when encrypting.

Q: What is the Transaction Counter in a Bitcoin block?

A: A field that lists the number of transactions stored in the block.

Q: What are Transactions in a Bitcoin block?

A: A list of all of the transactions within a block.

Q: What is Bitcoin mining?

A: The process by which transactions are officially entered on the blockchain.

Q: What are the steps involved in Bitcoin mining?

A: Transaction Verification, Hashing, Finding the Hash, Block Addition.

Q: What happens during Transaction Verification in Bitcoin mining?

A: When a transaction is made between wallets, the addresses and amount are entered into a block on the blockchain.

Q: What is Hashing in Bitcoin mining?

A: The block is assigned some information, and all of the data in the block is put through a cryptographic algorithm.

Q: What is Finding the Hash in Bitcoin mining?

A: Miners compete to find a hash that is equal to or less than a number set by the Bitcoin network’s difficulty algorithm.

Q: What happens during Block Addition in Bitcoin mining?

A: The first miner to find the solution to the problem receives bitcoins as a reward, and the process begins again.

Q: What do miners need for Bitcoin mining?

A: Substantial hardware and software, such as a GPU or an ASIC.