# uselesskey-core-negative-der
DER-specific negative fixture builders for deterministic corruption used by
`uselesskey` test utilities.
## Purpose
- Truncate DER vectors and flip bytes at deterministic offsets.
- Provide deterministic DER mutation helpers used for parser-failure fixtures.
- Keep DER behavior isolated as a small SRP microcrate.
This crate intentionally only manipulates byte shape and does not parse or
validate cryptographic semantics.