def get_sign_key(exported_session_key, magic_constant):
sign_key = hashlib.md5(exported_session_key + magic_constant).digest()<EOL>return sign_key<EOL>
3.4.5.2 SIGNKEY

:param exported_session_key: A 128-bit session key used to derive signing
    and sealing keys
:param magic_constant: A constant value set in the MS-NLMP documentation
    (constants.SignSealConstants)
:return sign_key: Key used to sign messages