Stream Cipher

5 minutes 5 Questions

Stream ciphers are symmetric encryption methods that process messages bit-by-bit, or a byte at a time, using a keystream. A keystream is an infinite sequence of pseudorandom bits derived from a key and a nonce value. Stream ciphers apply a bitwise XOR operation between the plaintext message and the keystream to produce the ciphertext. For decryption, the same operation with the same keystream is performed. Stream ciphers are advantageous for communication systems since they can dynamically encrypt data as it is streamed. Due to their low latency, they are particularly suited for fast communication channels and lightweight implementations. Common stream ciphers are RC4 and ChaCha20.

Complete Guide to Stream Cipher

Stream Cipher: is a method in cryptography where plaintext is combined with a cipher digit by digit. Unlike block ciphers that encrypt blocks of plaintext, Stream Cipher encrypts plaintext symbols one at a time. Stream ciphers fall under the category of symmetric key cipher where the same key is used for both encryption and decryption.

Importance: Due to its ability to encrypt data one bit at a time, it provides high security for data transmission. Its efficient performance in hardware and suitability for encrypting large data makes it highly valuable. Furthermore, it assures confidentiality and maintains the integrity of data.

How it works: Stream Cipher uses a pseudo-random cipher digit generator to generate a stream of bits, which is then combined with the plaintext bit-by-bit or byte-by-byte to produce the ciphertext. The process is reversed during decryption using the same pseudo-random sequence.

Exam Tips: Understanding the mechanism of Stream Cipher is vital for exams.
Consider the following:
* Highlight the difference between a block cipher and a stream cipher.
* Clearly understand the use of pseudo-random number generator in the process.
* Highlight the pros and cons of using Stream Cipher.
* Be able to describe how Stream Cipher ensures data security.

Test mode:

Exam (Timed)

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Question 1

A company wants to securely send data packets using an encryption method where each bit of the plaintext is encrypted with a separate bit of a continuous key stream. Which of the following techniques should they use?

Cipher Block Chaining (CBC) Synchronous stream cipher Electronic Codebook (ECB) Asynchronous stream cipher

Correct Answer: Synchronous stream cipher

Synchronous stream ciphers use a continuous key stream to encrypt plaintext bits individually, providing security and synchronous functionality.

Question 2

A company plans to use a stream cipher for video streaming on their website. Which of the following characteristics of stream ciphers is an advantage for this scenario?

Memory intensive Low latency Key reuse vulnerabilities Lack of hardware support

Correct Answer: Low latency

Stream ciphers have low latency as they encrypt data in real-time, bit-by-bit. This characteristic is advantageous for video streaming as it allows for smooth playback and minimal buffering.

Question 3

An IT company uses a stream cipher for secure communication between their servers. Recently, they experienced a security breach due to key reuse. Which of the following is the best solution?

Implement unique keys for each encryption session Use the same key with counter mode Switch to a different stream cipher Increase key length

Correct Answer: Implement unique keys for each encryption session

Key reuse in stream ciphers can lead to patterns and vulnerabilities. Using unique keys for each encryption session ensures that no patterns can be formed, hence maintaining security.

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