PKCS1_PSS.py 文件源码

def sign(self, mhash):
        """Produce the PKCS#1 PSS signature of a message.

        This function is named ``RSASSA-PSS-SIGN``, and is specified in
        section 8.1.1 of RFC3447.

        :Parameters:
         mhash : hash object
                The hash that was carried out over the message. This is an object
                belonging to the `Crypto.Hash` module.

        :Return: The PSS signature encoded as a string.
        :Raise ValueError:
            If the RSA key length is not sufficiently long to deal with the given
            hash algorithm.
        :Raise TypeError:
            If the RSA key has no private half.

        :attention: Modify the salt length and the mask generation function only
                    if you know what you are doing.
                    The receiver must use the same parameters too.
        """
        # TODO: Verify the key is RSA

        randfunc = self._key._randfunc

        # Set defaults for salt length and mask generation function
        if self._saltLen == None:
            sLen = mhash.digest_size
        else:
            sLen = self._saltLen
        if self._mgfunc:
            mgf = self._mgfunc
        else:
             mgf  = lambda x,y: MGF1(x,y,mhash)

        modBits = Crypto.Util.number.size(self._key.n)

        # See 8.1.1 in RFC3447
        k = ceil_div(modBits,8) # Convert from bits to bytes
        # Step 1
        em = EMSA_PSS_ENCODE(mhash, modBits-1, randfunc, mgf, sLen)
        # Step 2a (OS2IP) and 2b (RSASP1)
        m = self._key.decrypt(em)
        # Step 2c (I2OSP)
        S = bchr(0x00)*(k-len(m)) + m
        return S