[[zkr,Zkr]]
=== `Zkr` - Entropy Source Extension

The entropy source extension defines the `seed` CSR at address `0x015`. 
This CSR provides up to 16 physical `entropy` bits that can be used to
seed cryptographic random bit generators. 

See <<crypto_scalar_es>> for the normative specification and access control
notes. <<crypto_scalar_appx_es>> contains design rationale and further
recommendations to implementers.

