Module entropy 

Kernel entropy pool : a cryptographically sound random bytes from interrupt noise.

Collects entropy from:

• keyboard IRQ timing + scancode data
• timer tick jitter (low bits of TSC)
• storage (AHCI) IRQ timing
• RDRAND when available (as seed material)

The pool uses a tweaked Threefish-like mixing over 128 bytes (4×4 u64s) for efficient diffusion. Output is extracted by hashing the pool state through a compression round : no built-in hash dependency needed.

Constants

ENTROPY_HIGH_WATER 🔒

Entropy threshold in bytes before we consider the pool “initialised”.

POOL_WORDS 🔒

Number of 64-bit words in the entropy pool (16 = 128 bytes).

Statics

ENTROPY_CTR 🔒

Estimated entropy count (in bytes). Saturates at POOL_WORDS * 8.

POOL 🔒

The entropy pool : a 128‑byte array of 16 u64s.

POOL_IDX 🔒

Index where the next sample will be mixed in.

Functions

add_entropy

Feed a 64‑bit sample into the entropy pool (called from interrupt handlers).

extract_block 🔒

Extract 8 bytes from the pool by folding all words together.

fill_random

Fill a byte buffer with random bytes from the entropy pool.

is_ready

Check whether the entropy pool has accumulated enough entropy (at least ENTROPY_HIGH_WATER bytes). Used by GRND_NONBLOCK.

rdrand64 🔒

BUG TODO : RDRAND helper (used during boot seeding).

seed_from_rdrand

One-time boot‑time seed of the pool from RDRAND (if available).

twist 🔒

Non‑linear twist: multiplicative inverse in GF(2⁶⁴) masked by a prime, then XORed with a rotation of itself.