Stream Ciphers

What is Stream Cipher?

Stream ciphers are encryption methods that encrypt digital data bit by bit or byte by byte, producing an encrypted data stream. Unlike block ciphers, which encrypt data in fixed-length blocks, stream ciphers are well suited for real-time applications such as video streaming and online communication, where data delay and efficiency are critical factors.

The basic operation principle of a stream cipher encryption algorithm is quite straightforward. It consists of generating a key stream (or pseudo-random number series), which is then combined with the message at the bit level (often using XOR operation) to produce the encrypted message. The decoding process works in the same way: the encrypted message is XORed again with the same key stream to recover the original message.

Main algorithms

RC4

RC4 was long one of the most popular stream ciphers, and it was widely used in various security protocols, such as SSL/TLS and WEP. Its popularity was based on its simplicity and speed. However, the security of RC4 has been criticized over the years due to several vulnerabilities, and it is now considered outdated. Not recommended for use in security-critical applications.

Salsa20/ChaCha

Salsa20 and its variant ChaCha are modern stream ciphers designed to provide both speed and high level of security. They have gained popularity especially because of their strong security profile and efficiency. For example, ChaCha has been adopted in the TLS protocol and is recommended as an alternative in many security protocols. Salsa20 and ChaCha are good choices when fast and secure encryption method is needed.

AES-CTR

Although AES itself is a block cipher, its CTR (Counter) mode can be used as a stream cipher. AES-CTR combines the strong encryption performance of AES with the flexibility of a stream cipher, allowing data to be encrypted and decrypted in small pieces. AES-CTR is a widely accepted and used method that is part of several standards and protocols. It is a recommended choice when high security and performance are needed.

What are stream ciphers used for?

Stream ciphers are ideal in situations where data is constantly generated or consumed and where even a small delay or data buffering is problematic. This is why they are widely used in real-time data transfer, such as in online video, VoIP calls, and real-time data transfer. Their efficiency and ability to process data streams dynamically make them suitable for use in wireless and mobile devices, where processor power and battery life are limited resources.