Strømningskoder

Strømningskoder, also known as stream ciphers, are a type of symmetric encryption algorithm. Unlike block ciphers which encrypt data in fixed-size blocks, stream ciphers encrypt individual bits or bytes of plaintext. They achieve this by generating a pseudorandom keystream, which is then combined with the plaintext, typically using the XOR operation, to produce the ciphertext. The same process is used for decryption, where the keystream is XORed with the ciphertext.

The security of a stream cipher relies heavily on the quality of its pseudorandom number generator (PRNG). A good PRNG should produce a keystream that is indistinguishable from a truly random sequence, making it difficult for an attacker to predict or recover the keystream. If the keystream is compromised or reused for encrypting multiple messages, the cipher is vulnerable.

Stream ciphers are often faster than block ciphers and require less memory, making them suitable for applications where computational resources are limited or high throughput is required, such as in real-time communication protocols. They are widely used in various cryptographic systems, including secure communication protocols like TLS/SSL and in some wireless encryption standards. Examples of well-known stream ciphers include RC4, ChaCha20, and various variants of the International Data Encryption Algorithm (IDEA).