Keystream
A keystream is a sequence of cryptographic bits or symbols generated for combination with plaintext or ciphertext in a stream cipher.
Hacking Cryptography
A keystream is a sequence of cryptographic bits or symbols generated for combination with plaintext or ciphertext in a stream cipher.
- How it is used
- Explains keystream as the XOR input that lets stream ciphers encrypt arbitrarily long messages from a short seed.
- How deep it goes
- Works through CSPRNG, LFSR, and RC4 generation internals, then traces known-plaintext and statistical attacks.
- Examples
- Uses a 1 GB video, an LFSR-encrypted “ATTACK AT” timestamp, RC4 code, and weak-IV WEP packets.
- What you can do after
- Diagnose/debug with it by recovering known keystream positions and recognizing when generator output enables prediction or key recovery.
Real-World Cryptography
A keystream is the sequence of pseudorandom bytes generated by a stream-encryption construction and XORed with plaintext or ciphertext.
- How it is used
- Explains how stream ciphers and counter modes transform plaintext into ciphertext through XOR with generated bytes.
- How deep it goes
- Details generation, truncation, XOR, and nonce-reuse failure, while stopping short of formal security proofs.
- Examples
- Uses AES-CTR and ChaCha20 flows, including nonce-and-counter inputs, repeated block generation, truncation, and XOR.
- What you can do after
- Understand how to trace keystream encryption and diagnose nonce reuse as a confidentiality failure.
Related concepts
- pseudorandom generation algorithmproduced by · RC4's pseudorandom generation algorithm updates the cipher state and produces successive keystream bytes.
- linear feedback shift registerproduced by · A linear-feedback shift register is a deterministic shift-register mechanism whose next input bit is computed as a linear function of selected state bits.
- cryptographically secure random number generatorproduced by · A cryptographically secure random number generator produces computationally unpredictable values while resisting prediction and recovery of its internal state by feasible adversaries.
- stream cipherproduced by · A stream cipher is an encryption algorithm that combines plaintext sequentially with a generated keystream, typically using XOR.
- known-plaintext attackproduced by · A known-plaintext attack is a cryptanalytic method that uses plaintext and corresponding ciphertext to infer information about the encryption process or key.
- logical XORuses · Logical XOR is a binary operation that produces true when exactly one operand is true and false when both operands have the same truth value.
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