Stream ciphers are a class of encryption algorithms used in cryptography to secure digital communication. Unlike block ciphers, which encrypt data in fixed-size blocks, stream ciphers operate on individual bits or bytes of data one at a time. They are designed to efficiently and quickly encrypt and decrypt data in real-time, making them ideal for applications like secure communication channels and data streaming.
Examples of stream ciphers include the well-known RC4, which was widely used in the past in WEP (Wireless Equivalent Privacy) protocol but is now considered insecure due to vulnerabilities, and more modern ciphers like ChaCha20, which are designed to provide both speed and strong security.
Key characteristics of stream ciphers include:
- Pseudo-Randomness: Stream ciphers generate a stream of pseudo-random bits or bytes, often called the “keystream.” This keystream is combined with the plaintext using a mathematical operation (usually XOR) to produce the ciphertext. The security of the stream cipher depends on the unpredictability and randomness of this keystream.
- Synchronization: Stream ciphers require synchronization between the sender and receiver to ensure that the same keystream is used for encryption and decryption. Any deviation in synchronization can lead to decryption errors.
- Efficiency: Stream ciphers are computationally efficient and well-suited for applications where data is continuously transmitted, such as internet communication, voice calls, or streaming media. They can encrypt and decrypt data in small units, which minimizes latency and processing overhead.
- Key Management: The security of a stream cipher relies heavily on the secrecy of the encryption key. Proper key management practices are essential to prevent unauthorized access to the keystream and maintain the confidentiality of the communication.