Classic Encryption Flashcards

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Questions and Answers

What does 'plaintext' refer to?

Coded Message
Algorithm for transforming plaintext to ciphertext
Information used in cipher known only to the sender/receiver
Original Message (correct)

What is 'ciphertext'?

Algorithm for transforming plaintext
Information used in cipher
Original Message
Coded Message (correct)

What is a cipher?

Algorithm for transforming plaintext to ciphertext

What is a key in cryptography?

Information used in cipher known only to the sender/receiver Signup and view all the answers

What does encipher/encrypt mean?

Converting plaintext to ciphertext Signup and view all the answers

What does decipher mean?

Converting ciphertext to plaintext Signup and view all the answers

What is cryptography?

The study of encryption principles/methods Signup and view all the answers

What is cryptoanalysis?

Study of principles/methods of deciphering ciphertext without knowing the key Signup and view all the answers

What does cryptology encompass?

Field of both cryptography and cryptoanalysis Signup and view all the answers

What are the requirements for a symmetric cipher?

All of the above (D) Signup and view all the answers

What is the objective of cryptoanalysis?

To recover the key and not the message Signup and view all the answers

What are the two types of attacks used in cryptoanalysis?

Cryptanalytic Attack (A), Brute-Force Attack (B) Signup and view all the answers

What are the features of a cryptanalytic attack?

When only the ciphertext or, plaintext, chosen plaintext, chosen ciphertext, chosen text is known Signup and view all the answers

What does ciphertext only mean?

Only know algorithm, and ciphertext, is statistical, know or can identify plaintext Signup and view all the answers

What is known plaintext?

Know/suspect plaintext and ciphertext Signup and view all the answers

What does chosen plaintext mean?

Select plaintext and obtain ciphertext Signup and view all the answers

What is chosen ciphertext?

Select plaintext and obtain ciphertext Signup and view all the answers

What does chosen text mean?

Select plaintext or ciphertext to encrypt/decrypt Signup and view all the answers

What is a brute-force search?

The attacker tries every possible key on a piece of ciphertext until an intelligible translation into plaintext is obtained Signup and view all the answers

What are the two basic building blocks of all encryption techniques?

Transposition (B), Substitution (C) Signup and view all the answers

What are classical substitution ciphers?

Where characters of plaintext are replaced by other characters Signup and view all the answers

What is a Caesar cipher?

26 possible ciphers, brute force search Signup and view all the answers

What is a monoalphabetic cipher?

Rather than just shifting the alphabet, could simply jumble the letters randomly Signup and view all the answers

What is Playfair encryption?

The Playfair cipher is a substitution cipher that employs a table where one letter is omitted Signup and view all the answers

What is a multiletter substitution cipher?

Substitute m successive plaintext letters with m ciphertext letters Signup and view all the answers

What are transposition ciphers?

Hides the message by rearranging the letter order Signup and view all the answers

What are transposition/permutation ciphers?

These hide the message by rearranging the letter order without altering the actual letters used Signup and view all the answers

What are row transposition ciphers?

Writes letters of message out in rows over specified number of columns Signup and view all the answers

What is the Hill cipher?

Cmm = Kmm x Pm*m Signup and view all the answers

Study Notes

Key Concepts in Classic Encryption

Plaintext: The original message before encryption.
Ciphertext: The coded version of the plaintext after encryption.
Cipher: An algorithm designed to transform plaintext into ciphertext.
Key: A unique piece of information used in a cipher, known only to the sender and receiver.

Encryption and Decryption Processes

Encipher/Encrypt: The process of converting plaintext into ciphertext.
Decipher: The reverse process, transforming ciphertext back into plaintext.

Fields of Study

Cryptography: The science of encoding messages to maintain confidentiality.
Cryptoanalysis: The study aimed at deciphering ciphertext without needing the key.
Cryptology: The overarching field that combines both cryptography and cryptoanalysis.

Symmetric Ciphers Requirements

Requires a strong encryption algorithm and a secret key shared only between sender and receiver.
Assumes the encryption algorithm is publicly known.
Secure channels are necessary for key distribution.
Mathematical relationship exists where Y = EK(X) and X = DK(Y).

Objectives and Attacks in Cryptoanalysis

Objective: To recover the key used for encryption rather than the original message.
Types of Attacks: Cryptanalytic and brute-force attacks.
Cryptanalytic Attack Features: Based on known ciphertext, plaintext, chosen plaintext, or chosen ciphertext.

Types of Knowledge in Attacks

Ciphertext only: Knowing the encryption algorithm and ciphertext; relies on statistical analysis.
Known plaintext: Possessing both suspected plaintext and corresponding ciphertext.
Chosen plaintext: Picking specific plaintext to obtain the corresponding ciphertext.
Chosen ciphertext: Similar to chosen plaintext, used to gather ciphertext from selected plaintext.
Chosen text: Involves selecting plaintext or ciphertext for encrypting/decrypting purposes.

Brute-Force Search

The method of systematically testing every possible key to decode the ciphertext into intelligible plaintext.

Basic Components of Encryption Techniques

Substitution: Replacing plaintext characters or bit patterns with ciphertext characters or bit patterns.
Transposition: Rearranging the order of characters in the plaintext without changing the actual letters.

Classical Ciphers

Caesar Cipher: A rotational cipher with 26 possible shifts, susceptible to brute-force attacks.
Monoalphabetic Cipher: Jumbles the letters randomly, providing 26 unique keys for encryption.
Playfair Encryption: Uses a 5x5 grid to substitute letters, omitting one character from the alphabet.
Multiletter Substitution Cipher: Substitutes m plaintext letters with m ciphertext letters, exemplified by the Hill Cipher.

Transposition Ciphers

Employ letter rearrangement to obscure the message.
Row Transposition Ciphers: Write plaintext in rows across a specified number of columns, then reorder the columns based on a key before reading the rows.

Advanced Example

Hill Cipher: Uses matrix mathematics in the encryption process, encapsulating complex relationships between plaintext, ciphertext, and keys.

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Description

Test your knowledge of classic encryption terms with these flashcards. Each card provides a key term related to encryption along with its definition to help reinforce your understanding of the subject. Perfect for students learning about cryptography.