Classe « ElGamalobj »

Méthode Crypto.PublicKey.ElGamal.ElGamalobj.sign

Signature de la méthode sign

def sign(self, M, K) 

Description

sign.__doc__

Sign a piece of data with ElGamal.

        :Parameter M: The piece of data to sign with ElGamal. It may
         not be longer in bit size than *p-1*.
        :Type M: byte string or long

        :Parameter K: A secret number, chosen randomly in the closed
         range *[1,p-2]* and such that *gcd(k,p-1)=1*.
        :Type K: long (recommended) or byte string (not recommended)

        :attention: selection of *K* is crucial for security. Generating a
         random number larger than *p-1* and taking the modulus by *p-1* is
         **not** secure, since smaller values will occur more frequently.
         Generating a random number systematically smaller than *p-1*
         (e.g. *floor((p-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 be a cryptographic hash, otherwise an
         attacker may mount an existential forgery attack.

        :Return: A tuple with 2 longs.