Entropy source

As explained in Real-World Cryptography

An entropy source is a physical or computational process that supplies unpredictable or partially unpredictable input for random-data generation.

An entropy source is a physical or computational process that supplies unpredictable, or partly unpredictable, input for random-data generation. Operating systems gather such input from events including hardware interrupts, mouse movements, software interrupts, and disk-seek timing. section 8.1

Entropy describes how unpredictable a string is: predictable strings have low entropy, while less predictable strings have high entropy. Raw noise may be biased, insufficient, or predictable during events such as device startup, so relying on a single source can be dangerous. section 8.1

Common approaches include:

• Capture physical unpredictability, such as thermal noise or changing wax shapes in Cloudflare’s LavaRand wall, and convert it into random bytes. section 8.1
• Mix multiple entropy sources to obtain a seed for a pseudorandom number generator, which can produce many random values quickly. section 8.2

Inspect the LavaRand wall as a concrete illustration of extracting random bytes from unpredictable physical patterns. section 8.1

How Real-World Cryptography covers it

How deep it goes

Explains source types, entropy quality, startup predictability, physical randomness, and PRNG seeding without detailing extraction algorithms.

Examples

Uses mouse movement, interrupts, disk-seek timing, thermal noise, and Cloudflare’s LavaRand wall as examples.

What you can do after

Evaluate randomness pipelines by identifying entropy sources, recognizing weak startup conditions, and understanding why systems seed PRNGs.

How it connects

Connects entropy sources to entropy, operating systems, TRNGs, PRNGs, CSPRNGs, DRBGs, ASLR, and TCP.

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Also explained in

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  Hacking CryptographyA physical or computational process that supplies uncertain values from which random output can be derived.

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Related concepts

• crypto/rand packageused by · The crypto/rand package is Go’s standard-library package for generating cryptographically secure random data from system-provided entropy sources.
• cryptographically secure random number generatorused by · A cryptographically secure random number generator produces computationally unpredictable values while resisting prediction and recovery of its internal state by feasible adversaries.
• pseudo-random number generatoruses · A pseudorandom number generator is a deterministic computational process that uses an initial seed or internal state to produce a sequence with random-like statistical properties.
• operating systemused by · An operating system is system software that manages computer hardware and provides services and interfaces for application programs.
• true random number generatorused by · A true random number generator produces unpredictable values by sampling nondeterministic physical phenomena rather than relying solely on deterministic algorithms.

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