backend.py 文件源码

def _parameter_bytes(self, encoding, format, cdata):
        if encoding is serialization.Encoding.OpenSSH:
            raise TypeError(
                "OpenSSH encoding is not supported"
            )

        # Only DH is supported here currently.
        q = self._ffi.new("BIGNUM **")
        self._lib.DH_get0_pqg(cdata,
                              self._ffi.NULL,
                              q,
                              self._ffi.NULL)
        if encoding is serialization.Encoding.PEM:
            if q[0] != self._ffi.NULL:
                write_bio = self._lib.PEM_write_bio_DHxparams
            else:
                write_bio = self._lib.PEM_write_bio_DHparams
        elif encoding is serialization.Encoding.DER:
            if q[0] != self._ffi.NULL:
                write_bio = self._lib.Cryptography_i2d_DHxparams_bio
            else:
                write_bio = self._lib.i2d_DHparams_bio
        else:
            raise TypeError("encoding must be an item from the Encoding enum")

        bio = self._create_mem_bio_gc()
        res = write_bio(bio, cdata)
        self.openssl_assert(res == 1)
        return self._read_mem_bio(bio)