Mastering Blockchain - Second Edition

Stream ciphers

Stream ciphers are encryption algorithms that apply encryption algorithms on a bit-by-bit basis (one bit at a time) to plaintext using a keystream. There are two types of stream ciphers: synchronous stream ciphers and asynchronous stream ciphers:

• Synchronous stream ciphers are those where the keystream is dependent only on the key
• Asynchronous stream ciphers have a keystream that is also dependent on the encrypted data

In stream ciphers, encryption and decryption are the same function because they are simple modulo-2 additions or XOR operations. The fundamental requirement in stream ciphers is the security and randomness of keystreams. Various techniques ranging from pseudorandom number generators to true random number generators ...