Is it correct that a stream cipher using a truly random key binary sequence is the unbreakable One-Time Pad cipher?
A stream cipher is a type of encryption algorithm that operates on individual bits or bytes of plaintext and produces a corresponding stream of ciphertext. It is based on the use of a key stream, which is generated by combining a secret key with a random or pseudorandom sequence of bits. The key stream is then combined with the plaintext using a bitwise XOR operation to produce the ciphertext.
The One-Time Pad (OTP) cipher is a specific type of stream cipher that is considered to be unbreakable if certain conditions are met. In the OTP cipher, the key stream is generated by using a truly random sequence of bits that is at least as long as the plaintext. The key stream is never reused and is kept secret from the adversary. The key stream is combined with the plaintext using a bitwise XOR operation to produce the ciphertext.
The security of the OTP cipher relies on two main principles: perfect secrecy and the randomness of the key stream. Perfect secrecy means that the ciphertext provides no information about the plaintext, even if the adversary has unlimited computational power. This property is achieved by using a key stream that is completely random and independent of the plaintext.
If a stream cipher uses a truly random key binary sequence, it can be considered as an implementation of the OTP cipher. In this case, the key stream is generated using a source of true randomness, such as a physical process like radioactive decay or atmospheric noise. The key stream is truly random and satisfies the requirements of the OTP cipher.
However, it is important to note that the practical implementation of a truly random key binary sequence is challenging. Generating and distributing truly random keys in a secure manner can be difficult in practice. Additionally, the key must be at least as long as the plaintext, which can be impractical for large amounts of data.
In contrast, many stream ciphers use pseudorandom number generators (PRNGs) to generate the key stream. PRNGs are deterministic algorithms that produce sequences of numbers that appear to be random, but are actually generated using a fixed-length seed value. While PRNGs can be secure if implemented correctly, they are not truly random and can be vulnerable to attacks.
A stream cipher using a truly random key binary sequence can be considered as an unbreakable OTP cipher. However, generating and distributing truly random keys in a secure manner can be challenging in practice. It is important to carefully consider the implementation and key generation process when using stream ciphers.
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