rwrandread

rwrandread is a term that appears as the name of a function or routine in several software projects, rather than a single, standardized API. It is typically used to denote a procedure that reads random data from a randomness source into a caller-supplied buffer. Because there is no universal specification for rwrandread, its exact signature, return value, and guarantees vary by implementation.

Common characteristics

- Purpose: to supply cryptographic-quality or otherwise unpredictable bytes for use in key generation, nonce creation, seeding of PRNGs, or testing.

- Parameters: in many implementations, rwrandread takes a pointer to a buffer and a length, and fills the buffer with random bytes.

- Return value: typically the number of bytes successfully read, with error signaling through a negative value or an exception in higher-level languages.

- Behavior: implementations may block until sufficient entropy is available or may operate in a non-blocking mode, depending on the underlying randomness source.

Sources of randomness

- Operating system sources: cryptographic-quality randomness may be obtained from OS facilities such as /dev/random, /dev/urandom, or platform APIs like getrandom.

- Hardware RNGs: some implementations use hardware-based secure random number generators (for example, CPU RNG instructions or dedicated chips) as sources of entropy.

- PRNG wrappers: certain rwrandread variants may seed or reseed a pseudorandom number generator with entropy obtained from a more secure source.

Security considerations

- Quality and bias: cryptographic use typically requires unbiased, unpredictable output with proper entropy management.

- Portability and guarantees: because implementations differ, callers should review local documentation to understand blocking behavior, entropy sourcing, and thread safety.

See also

Entropy, cryptographic random number generators, getrandom, /dev/random, /dev/urandom, rdrand.