Stream Ciphers and Pseudo-Random Number Generators What is a Stream Cipher? A stream cipher is a cryptographic algorithm that processes a sequence of pl...
Stream Ciphers and Pseudo-Random Number Generators
What is a Stream Cipher?
A stream cipher is a cryptographic algorithm that processes a sequence of plaintext characters (data) and transforms it into ciphertext (an encrypted version). It operates by encrypting each character of the plaintext with a secret key, ensuring that only authorized parties can read the data.
How does a Stream Cipher Work?
The plaintext is divided into a series of fixed-length blocks.
Each block is encrypted using the secret key.
The encrypted blocks are then interleaved with the original plaintext, creating an encrypted stream.
Only someone with the correct key can decrypt the stream, revealing the original plaintext.
What is a Pseudo-Random Number Generator (PRNG)?
A PRNG is a mathematical algorithm that generates random numbers based on a set of seed values. Seed values are typically chosen at random and can be any length, ensuring that the generated numbers are unpredictable.
How is a PRNG Used in Symmetric Key Cryptography?
PRNGs are used to generate the keystream for a stream cipher. The keystream is a sequence of random numbers that are used to encrypt and decrypt the plaintext. By using a secure PRNG, the encryption and decryption process becomes more robust against attacks.
Example:
Let's say we have a plaintext message "Hello, world!" and a secret key "secret". The stream cipher would work as follows:
The plaintext is divided into 6 blocks (each 6 characters long).
Each block is encrypted with the secret key.
The encrypted blocks are then interleaved in the order they appear in the plaintext.
The resulting encrypted stream is "ZIVRHUO".
This stream can be decrypted using the same key, revealing the original plaintext.
Conclusion:
Stream ciphers and PRNGs are essential concepts in symmetric key cryptography. Stream ciphers provide a secure way to encrypt data by transforming it into an unintelligible cipher stream. PRNGs generate random numbers that are used to create the keystream for the stream cipher, making it more resistant to attacks