def didGen64(vk64u, method="dad"):
    """
    didGen accepts a url-file safe base64 key in the form of a string and returns a DID.

    :param vk64u: base64 url-file safe verifier/public key from EdDSA (Ed25519) key
    :param method: W3C did method string. Defaults to "dad".
    :return: W3C DID string
    """
    if vk64u is None:
        return None

    return "did:{0}:{1}".format(method, vk64u)