Cryptography Module 2

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Questions and Answers

What is the primary goal of cryptography?

To communicate securely between two parties (correct)

To develop a new encryption algorithm

To encrypt and decrypt messages quickly

To create a secure network infrastructure

What is the type of encryption where the sender and receiver use the same key?

Public key encryption

Asymmetric key encryption

Conventional decryption

Symmetric key encryption (correct)

What is the main difference between block cipher and stream cipher?

Block cipher processes input in blocks, stream cipher processes input continuously (correct)

Block cipher is used for encryption, stream cipher is used for decryption

Block cipher is faster, stream cipher is slower

Block cipher is used for symmetric key encryption, stream cipher is used for asymmetric key encryption

What is an example of current application of cryptography?

Attesting the identity of a web server Signup and view all the answers

What is the classification of cryptography that uses a single, common key for encryption and decryption?

Symmetric key cryptography Signup and view all the answers

What is the main purpose of cryptography in online transactions?

To protect the confidentiality of online transactions Signup and view all the answers

What is the classification of cryptography that uses different keys for encryption and decryption?

Asymmetric key cryptography Signup and view all the answers

What is the term for the person who reads a message without the sender's permission?

Eavesdropper Signup and view all the answers

What is the original intelligible message called in cryptography?

Plaintext Signup and view all the answers

What is the process of converting plaintext to cipher text called?

Encipher Signup and view all the answers

What is the study of principles and methods of transforming an unintelligible message back into an intelligible message without knowledge of the key called?

Cryptanalysis Signup and view all the answers

What is the critical information used by the cipher, known only to the sender and receiver?

Key Signup and view all the answers

What is the term for both cryptography and cryptanalysis?

Cryptology Signup and view all the answers

What is the algorithm for transforming an intelligible message into an unintelligible one using a code-book?

Code Signup and view all the answers

What is the process of converting cipher text back into plaintext using a cipher and a key?

Decipher Signup and view all the answers

What are the two general principles that all encryption algorithms are based on?

Substitution and transposition Signup and view all the answers

What is the most popular symmetric-key system?

Data Encryption Standard (DES) Signup and view all the answers

What type of cipher encrypts a single bit at a time?

Data Encryption Standard (DES) Signup and view all the answers

What is a method of encryption by which the positions held by units of plaintext are shifted according to a regular system?

Transposition Ciphers Signup and view all the answers

What is a method of encryption by which units of plaintext are replaced with ciphertext, according to a fixed system?

Substitution Ciphers Signup and view all the answers

What type of cipher encrypts the same plaintext bit or byte to a different bit or byte every time it is encrypted?

Stream Ciphers Signup and view all the answers

What type of cipher applies a deterministic algorithm along with a symmetric key to encrypt a block of text?

Block Ciphers Signup and view all the answers

What type of cryptography uses different keys for encrypting and decrypting the information?

Asymmetric Key Cryptography Signup and view all the answers

What is a characteristic of asymmetric key cryptography?

Different keys are used for encrypting and decrypting the information Signup and view all the answers

Study Notes

Cryptography

The art or science of transforming an intelligible message into an unintelligible one, and then retransforming it back to its original form.

Terminology

Plaintext: The original intelligible message.
Cipher text: The transformed message.
Cipher: An algorithm for transforming an intelligible message into an unintelligible one.
Key: Critical information used by the cipher, known only to the sender and receiver.
Encipher (encode): The process of converting plaintext to cipher text using a cipher and a key.
Decipher (decode): The process of converting cipher text back into plaintext using a cipher and a key.
Cryptanalysis: The study of principles and methods of transforming an unintelligible message back into an intelligible one without knowledge of the key (also called code breaking).
Cryptology: Both cryptography and cryptanalysis.
Code: An algorithm for transforming an intelligible message into an unintelligible one using a code-book.

Classification of Cryptographic Systems

Classified along 3 independent dimensions: • Type of operations used for transforming plaintext to cipher text. • Type of operations used for transforming plaintext to cipher text. • The way in which the plaintext is processed.

Types of Operations

Substitution: Each element in the plaintext is mapped into another element.
Transposition: Elements in the plaintext are rearranged.

Type of Keys

Symmetric key (or single key or conventional encryption): The sender and receiver use the same key.
Public key encryption: The sender and receiver use different keys.

Way of Processing

Block cipher: Processes the input and block of elements at a time, producing output block for each input block.
Stream cipher: Processes the input elements continuously, producing output element one at a time, as it goes along.

History of Cryptography

Began primarily as a way for two parties to communicate securely, even if their messages might be read by an eavesdropper.

Applications of Cryptography

Attesting the identity of the organization operating a web server.
Digitally signing electronic documents.
Protecting the confidentiality of online banking and shopping transactions.
Protecting the confidentiality of files stored on a hard drive.
Protecting the confidentiality of packets sent over a wireless network.

Categories of Cryptography

Symmetric key cryptography.
Asymmetric key cryptography.

Symmetric Key Cryptography

An encryption system in which the sender and receiver of a message share a single, common key.
The most popular symmetric–key system is the Data Encryption Standard (DES).

Types of Symmetric Key Cryptography

Classical cryptography: • Transposition ciphers: A method of encryption by which the positions held by units of plaintext are shifted according to a regular system. • Substitution ciphers: A method of encryption by which units of plaintext are replaced with ciphertext, according to a fixed system.
Modern cryptography: • Stream ciphers: The same plaintext bit or byte will encrypt to a different bit or byte every time it is encrypted. • Block ciphers: An encryption method that applies a deterministic algorithm along with a symmetric key to encrypt a block of text.

Asymmetric Key Cryptography

The encryption process where different keys are used for encrypting and decrypting the information.
Keys are different but are mathematically related, such that retrieving the plain text by decrypting ciphertext is feasible.

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Description

Learn about the principles and methods of transforming intelligible messages into unintelligible ones and back to their original form. Explore terminology such as plaintext, ciphertext, and more.