Deterministic ECDSA Signatures.

Would standardise a single way to make ECDSA signatures, so a given key and message always give the same signature.

A signing device has some free choice when it makes a signature, and bad firmware could use that to leak your secret key. If every device follows this one method, you can load the same key into two devices, sign the same message on both, and compare: any difference shows one of them is misbehaving.