@alex I originally wrote this in the ``DSA`` test because the NIST vectors provide ``r`` and ``s`` values instead of ``DER`` encoded signatures while OpenSSL's ``DSA_sign`` and ``DSA_verify`` deal with ``DER`` encoded signatures. Then @reaperhulk enlightened me to the fact that any backend will have to implement a similar function to be able to run our tests on the NIST vectors, hence the backend interface and implementation..