Random Bit Generator

Many cryptographic algorithms require cryptographically secure random data. These random data come from two classes of random bit generators (RBGs): non-deterministic RBGs and deterministic RBGs. Non-deterministic RBGs typically incorporate hardware components that use measurements of the physical environment. Deterministic random bit generators, or DRBGs, on the other hand, produce a deterministic output given the same seed. DRBGs typically use either a hash or cipher function on top of non-deterministic entropy gathering to seed itself. For further implementation details, see this blog post.

Deterministic Random Bit Generator

O(1) Cryptography provides DRBGs based on NIST SP 800-90A rev1 with perfect forward secrecy using ratcheting and automatic reseeding. The primary implementation is based on BLAKE3 comparable to the HMAC_CTR strategy. Random data are generated for various cryptographic uses via thread-safe DRBGs through the following SPI.

C SPI

void drbg_randombytes(void *buf, unsigned long bytes);

Java SPI

public interface RandomBytesGenerator {
    byte[] generateBytes(int nrBytes);
}

Seeds and Entropy

Seeds are used to initialize and reinitialize instances of deterministic random bit generators (DRBGs) with entropy. For example, a DRBG based on a stream cipher with s bytes of internal state can be seeded with s bytes of entropy. Operating systems provide various low level APIs for obtaining system entropy, and these sources are exposed through the following SPI.

C SPI

void drbg_entropy(void *buf, unsigned long bytes);

Java SPI

public interface SeedGenerator {
    byte[] generateSeed(int nrBytes);
}