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Term | Definition |
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True or False: The smaller the encryption key is, the more secure the encrypted data is. | False; The larger the key, the more secure the encrypted data will be. |

What's the difference between a stream cipher and a block cipher? A. Block ciphers are only used for block device encryption. B. Stream ciphers encrypt data as a continuous stream, while block ciphers operate on chunks of data. C. There is no difference. D. Stream ciphers can't save encrypted data to disk. | B. Stream ciphers encrypt data as a continuous stream, while block ciphers operate on chunks of data. |

What makes an encryption algorithm symmetric? A. High speed B. The same keys used for encryption and decryption C. Very large key sizes D. Different keys used for encryption and decryption | B. The same keys used for encryption and decryption |

What is steganography? A. The study of stegosauruses B. The practice of encoding messages C. The study of languages D. The practice of hiding messages | D. The practice of hiding messages |

What are the components that make up a cryptosystem? Select all that apply. A. Decryption algorithms B. Key generation algorithms C. Encryption algorithms D. Transmission algorithms | A. Decryption algorithms B. Key generation algorithms C. Encryption algorithms |

What is the downside of using symmetric encryption? | While having one shared secret that both encrypts and decrypts seems convenient up front, this can actually introduce some complications. |

What are two benefits of using symmetric encryption? | 1. Because of the symmetric nature of the encryption and decryption process, it's relatively easy to implement and maintain. 2. Symmetric algorithms are also very fast and efficient at encrypting and decrypting large batches of data. |

Why is GCM popular? | This is due to its security being based on AES encryption, along with its performance, and the fact that it can be run in parallel with great efficiency. |

GCM (Galois Counter Mode) | Works by taking randomized seed value, incrementing this and encrypting the value, creating sequentially numbered blocks of ciphertexts. The ciphertexts are then incorporated into the plaintext to be encrypted. |

TLS 1.2 with AES GCM | A specific mode of operation for the AES block cipher that essentially turns it into a stream cipher. |

What is the preferred secure configuration? | TLS 1.2 with AES GCM |

Why have most major web browsers dropped support for RC4 entirely, along with all versions of SSL, and use TLS instead? | In 2015, RC4 was dropped in all versions of TLS because of inherent weaknesses. |

What popular encryption protocols used RC4? | WEP, WPA, and SSL |

Since the RC4 NOMORE attack is an attack on the RC4 cipher itself, any protocol that uses this cipher is what? | Potentially vulnerable to the attack. |

What happened in the RC4 NOMORE attack? | This attack was able to recover an authentication cookie from a TLS-encrypted connection in just 52 hours. |

The RC4 cipher itself has inherent weaknesses and vulnerabilities that aren't only theoretically possible, there are lots of examples showing RC4 being broken, except by what? | The weakness of RC4 isn't due to brute-force attacks due to the key sizes supported. |

What key sizes does RC4 support? | Sizes from 40-bits to 2,048-bits. |

RC4 (Rivest Cipher 4) | A symmetric stream cipher that gained widespread adoption because of its simplicity and speed. |

Why do modern CPUs from Intel or AMD have AES instructions built into the CPUs themselves? | This allows for far greater computational speed and efficiency when working on cryptographic workloads. |

Cryptographic operations wind up being performed very often by devices. What does this mean in terms of speed? | The faster they can be accomplished with the minimal impact to the system, the better. |

Why is speed important when considering various encryption algorithms? | Sometimes data will be encrypted by running the data through the cipher multiple times. |

Why do some platforms implement cryptographic algorithms in hardware? | To accelerate the processes and remove some of the burden from the CPU. |

Why shouldn't an algorithm be overly difficult to implement, ideally? | Complicated implementation can lead to errors and potential loss of security due to bugs introduced in implementation. |

What two factors are important to keep in mind when considering various encryption algorithms? | 1. Speed 2. Ease of implementation |

What does it mean that encryption algorithms are the overall designs of the ciphers themselves? | These designs then must be implemented in either software or hardware before the encryption functions can be applied and put to use. |

Because of the large key size, brute-force attacks on AES are what? | Only theoretical right now, because the computing power required (or time required using modern technology) exceeds anything feasible today. |

AES is the first and only public cipher that's approved for what? | For use with top secret information by the NSA. |

AES (Advanced Encryption Standard) | A symmetric block cipher that uses a 128-bit block size and a 128-bit, 192-bit, or 256-bit key size. Practically uncrackable. |

In 1998 the EFF decrypted a DES-encrypted message in only 56 hours. What did this lead to? | Because of the inherent weakness of the small key size of DES, replacement algorithms were designed and proposed. This lead to the adopting of AES in 2001. |

What is an encryption standard used by WPA2 and is currently the strongest encryption standard used by Wi-Fi? | AES |

NIST | National Institute of Standards & Technology |

EFF | Electronic Frontier Foundation |

For encryption, what would protect against a brute force attack? | Longer key lengths |

What is one attack method that is to guess the key and see if the message decodes correctly? | A brute-force attack |

Why is key length important in cryptography? | It essentially defines the maximum potential strength of the system. |

What is the key size? | Defined in bits, it is the total number of bits or data that comprises the encryption key. |

The key is the unique piece that protects your data and the symmetric key must be what? | Kept secret to ensure the confidentiality of the data being protected. |

In symmetric encryption algorithms, the same key is used to encrypt as to what? | As to decrypt, everything else being the same. |

Parity checking | A data transmission control in which the receiving device recalculates the parity bit to verify accuracy of transmitted data. |

Why is the real world key length for DES only 56-bits? | Though the key size is technically 64-bits in length, 8-bits are used only for parity checking. |

DES (Data Encryption Standard) | A symmetric block cipher that uses 64-bit key sizes and operates on blocks 64-bits in size. |

What was one of the earliest encryption standards designed by IBM in the 1970s and adopted as a federal standard for encrypting and securing government data? | DES |

FIPS | Federal Information Processing Standards |

What is a good example of the use of an IV? | This can be seen when inspecting the 802.11 frame of a WEP encrypted wireless packet. The IV is included in plaintext right before the encrypted data payload. |

What is the idea behind an initialization vector? | If you have one shared master key, then generate a one-time encryption key. That encryption key is used only once by generating a new key using the master one and the IV. In order for the encrypted message to be decoded, the IV must be sent in plaintext along with the encrypted message. |

What is a bit of random data that's integrated into the encryption key and the resulting combined key is then used to encrypt the data? | An initialization vector |

How does an initialization vector work? | Using an initialization vector changes the binary sequence corresponding to each letter, enabling the letter "a" to be represented by a particular sequence in the first instance, and then represented by a completely different binary sequence in the second instance. |

Initialization Vector (IV) | A random number used in combination with a secret key as a means to encrypt data. This number is sometimes referred to as a nonce, or "number occuring once," as an encryption program uses it only once per session. |

What is used to avoid key reuse? | Initialization vector (IV) |

With stream ciphers, what happens if the key generation and handling isn't done properly, if the same key is used to encrypt data two or more times? | It's possible to break the cipher and to recover the plaintext. |

Generally speaking, what are the pros and cons of stream ciphers? | They are faster and less complex to implement, but they can be less secure than block ciphers. |

With block ciphers, what happens when the data to be encrypted isn't big enough to fill the block? | The extra space will be padded to ensure the plaintext fits into the blocks evenly. |

Block ciphers | The cipher takes data in, places it into a bucket or block of data that's a fixed size, then encodes that entire block as one unit. |

What two categories can symmetric key ciphers be placed into? | 1. Block ciphers 2. Stream ciphers |

Stream cipher | Takes a stream of input and encrypts the stream one character or one digit at a time, outputting one encrypted character or digit at a time. |

What is a Caesar cipher that uses a key of 13? | ROT13 |

ROT13 | A substitution cipher that uses a key of 13. To encrypt a message, you would rotate each letter 13 spaces. To decrypt a message, you would rotate each letter 13 spaces. |

Caesar Cipher | A substitution cipher that shifts characters a certain number of positions in the alphabet. |

Substitution cipher | An encryption mechanism that replaces parts of your plaintext with ciphertext. |

Symmetric Key Algorithm | Any encryption method that uses the same key for both encryption and decryption. |

Why is there concern that modern encryption could be at risk of being broken as quantum computing continues to develop? | Most modern encryption algorithms are based on large prime number factorization being computationally difficult, something that can be significantly sped up by quantum computing. Because of this, quantum computing would allow for significantly faster factorization and brute force attacks on encryption keys. |

What do modern steganographic techniques include? | Embedding messages and even files into other files like images or videos. |

Steganography | The practice of hiding information from observers, but not encoding it. |

Why would frequency analysis be important? | Some ciphers, especially classical transposition and substitution ciphers, preserve the relative frequency of letters in the plaintext and so are potentially vulnerable to this type of analysis. |

What is the premise behind frequency analysis? | In written languages, certain letters appear more frequently than others, and some letters are more commonly grouped together than others. |

Frequency analysis | The practice of studying the frequency with which letters appear in a ciphertext. |

Cryptanalysis | The process of decrypting a message without knowing the cipher or key used to encrypt it. |

Kerchoff's principle may also be referred to as what? | 1. Shannon's maxim or "the enemy knows the system" |

Cryptosystem | A collection of algorithms for key generation and encryption and decryption operations that comprise a cyptographic service. |

Kerchoff's Principle | A cryptosystem should be secure even if everything about the system, except the key, is public knowledge. |

True or False: Security through obscurity is something that you should rely on for securing communication or systems. | False |

Security through obscurity | Relying upon the secrecy or complexity of an item as its security, instead of practicing solid security practices. |

Without the key, what would happen? | Anyone using the same algorithm would be able to decode your message. |

Key | Component of a cipher which introduces something unique into your cipher. |

What is the underlying logic of process that's used to convert the plaintext into ciphertext? | Encryption algorithm |

Encryption algorithm | A set of steps that can convert readable plaintext into unreadable ciphertext. |

A cipher is made up of what two components? | 1. The encryption algorithm 2. The key |

Decryption | The process of converting a ciphertext back into plaintext. |

Encryption | The act of taking a message, called plaintext, and applying an operation to it, called a cipher, so that you receive a garbled, unreadable message as the output, called ciphertext. |

Cryptography | The art of protecting information by transforming it into an unreadable format, called cipher text. |