'Sign a piece of data with DSA.
:Parameter M: The piece of data to sign with DSA. It may
not be longer in bit size than the sub-group order (*q*).
:Type M: byte string or long
:Parameter K: A secret number, chosen randomly in the closed
range *[1,q-1]*.
:Type K: long (recommended) or byte string (not recommended)
:attention: selection of *K* is crucial for security. Generating a
random number larger than *q* and taking the modulus by *q* is
**not** secure, since smaller values will occur more frequently.
Generating a random number systematically smaller than *q-1*
(e.g. *floor((q-1)/8)* random bytes) is also **not** secure. In general,
it shall not be possible for an attacker to know the value of `any
bit of K`__.
:attention: The number *K* shall not be reused for any other
operation and shall be discarded immediately.
:attention: M must be a digest cryptographic hash, otherwise
an attacker may mount an existential forgery attack.
:Return: A tuple with 2 longs.
.. __: http://www.di.ens.fr/~pnguyen/pub_NgSh00.htm'

def sign(self, M, K):

    return pubkey.pubkey.sign(self, M, K)
