aeat.adapters.persistence.storage.master_key._zeroise module

In-memory zeroisation primitives for the master-key surface.

The substrate holds the unlocked KEK and DEK in bytearray buffers attached to a BucketSession instance. On lock the session calls into this module to overwrite each buffer with zero bytes before dropping the reference, so a memory-disclosure bug elsewhere (a debug traceback, a post-mortem core dump) cannot surface the key bytes.

Honest contract: zeroisation in Python is best-effort. The interpreter may have produced short-lived bytes copies of the buffer during property reads (BucketSession.kek materialises bytes(self._kek_buffer) on each access); the garbage collector owns the lifetime of those copies and there is no portable Python primitive that can reach them. The substrate confines KEK / DEK plaintext to bytearray containers and overwrites them at lock so the steady-state in-memory copy is zeroed; the transient bytes view lifetimes are bounded by GC.

A future native-extension wipe (CRYPTO_cleanse, SecureZeroMemory) would tighten this guarantee but is out of scope for this module.

zeroise(buffer)

Overwrite every byte of a mutable buffer with zero.

This is the canonical wipe-primitive consumed by BucketSession.close(). The function operates in place; the caller’s reference still points at the same bytearray object after the call returns, but every byte has been replaced by 0x00.

Parameters:

buffer (object) – Must be a bytearray. Any other type is rejected at runtime with TypeError.

Raises:

MasterKeyTypeError – When buffer is not a bytearray.

Return type:

None