Cryptography: Foundations, History, Security, and Applications

All flashcards

What is cryptography?

The practice and study of methods and protocols for protecting information and communication in the presence of adversaries.

How do plaintext and ciphertext differ?

Plaintext is the original readable or usable information; ciphertext is the transformed output intended to be unintelligible without the appropriate key.

What is a cryptographic key?

Information that controls how a cipher operates. Appropriate key management is central to protecting messages.

How does a code differ from a cipher?

A code substitutes meaningful units such as words or phrases with other units. A cipher systematically transforms smaller elements, such as letters or letter groups.

What do cryptography and cryptanalysis study?

Cryptography develops and uses methods to protect information; cryptanalysis studies ways to obtain information or defeat protection without the normally required key.

Quiz questions

1. What is plaintext?Answer: The original readable or usable information before encryption.
2. What does decryption do?Answer: It uses the appropriate method and key to recover plaintext from ciphertext.
3. In technical cryptography, what distinguishes a code from a cipher?Answer: A code replaces meaningful units such as phrases, while a cipher transforms smaller elements such as letters.
4. Why is key secrecy important in a well-designed cipher?Answer: The key controls the cipher, so exposure may let an attacker recover protected messages.
5. Which approach can help two parties establish secure communication without first sharing a secret key?Answer: Asymmetric cryptography, which uses related public and private keys.