How deeply does Hacking Cryptography cover stream cipher?

Explains XOR, one-time pads, CSPRNG keystreams, keystream reuse, LFSRs, RC4, and concrete attacks.

Stream cipher

A stream cipher is an encryption technique that combines plaintext with a generated keystream, typically one bit or symbol at a time.

A stream cipher encrypts plaintext one bit or byte at a time by XORing it with a generated keystream. It targets confidentiality in constrained devices and high-performance systems such as real-time video calls. section 4.0 section 5.6

A short seed initializes a cryptographically secure pseudorandom number generator (CSPRNG). Its output supplies as much keystream as needed, while the seed remains the fixed-length key. Recovering keystream bytes from known plaintext should not reveal the seed or predict future output. section 4.1.2

Equation 4.1

\[\text{Plaintext} \oplus \text{Key} = \text{Ciphertext} \label{equation:encrypt-xor}\]

The core operation combines plaintext and keystream with XOR to produce ciphertext. section 4.1.2

Treat these implementation rules as security boundaries:

Never reuse the same keystream for two messages: XORing the ciphertexts exposes the XOR of their plaintexts. section 4.1.2 section 4.4
Prefer a CSPRNG over a directly generated or predictable key stream; ordinary linear feedback shift registers can be reversed from their linear output. section 4.1.2 section 4.4
Do not treat RC4 as safe merely because it is simple: statistical biases in its Wi-Fi use enabled recovery of WEP passwords. section 4.3 section 4.4

Encrypting a large video

A one-time pad for a 1 GB video requires sharing a 1 GB random key. A stream cipher instead shares a CSPRNG seed; both parties generate matching 1 GB keystreams locally and XOR them with the video. section 4.1.2

How Hacking Cryptography covers it

liveBook manning.com

Read Hacking Cryptography on liveBook Get the book at manning.com

Related concepts

paddingcontrasts with · Padding is the addition of extra space, values, or data around or within a structure to satisfy size, alignment, layout, or processing requirements.
block ciphercontrasts with · A block cipher is a keyed symmetric cryptographic algorithm that transforms fixed-size blocks of data into ciphertext.
counter mode encryptionimplemented by · Counter mode encryption generates a keystream by encrypting successive counter values with a block cipher and combines it with plaintext to produce ciphertext.
cipher feedback modeimplemented by · Cipher feedback mode generates a keystream by feeding ciphertext back into a block cipher and is self-synchronizing.
output feedback modeimplemented by · Output feedback mode repeatedly encrypts an internal feedback value, typically an initialization vector, to generate a keystream independent of ciphertext.
keystreamproduces · A keystream is a sequence of cryptographic bits or symbols generated for combination with plaintext or ciphertext in a stream cipher.

This explainer was generated by Manning's knowledge graph from the text of Hacking Cryptography. The section links point to the parts of the book it draws on.