def verify(self, mhash, S):
        """Verify that a certain PKCS#1 PSS signature is authentic.
    
        This function checks if the party holding the private half of the given
        RSA key has really signed the message.
    
        This function is called ``RSASSA-PSS-VERIFY``, and is specified in section
        8.1.2 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.
         S : string
                The signature that needs to be validated.
    
        :Return: True if verification is correct. False otherwise.
        """
        # TODO: Verify the key is RSA
    
        # 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 8.1.2 in RFC3447
        k = ceil_div(modBits,8) # Convert from bits to bytes
        # Step 1
        if len(S) != k:
            return False
        # Step 2a (O2SIP), 2b (RSAVP1), and partially 2c (I2OSP)
        # Note that signature must be smaller than the module
        # but RSA.py won't complain about it.
        # TODO: Fix RSA object; don't do it here.
        em = self._key.encrypt(S, 0)[0]
        # Step 2c
        emLen = ceil_div(modBits-1,8)
        em = bchr(0x00)*(emLen-len(em)) + em
        # Step 3
        try:
            result = EMSA_PSS_VERIFY(mhash, em, modBits-1, mgf, sLen)
        except __HOLE__:
            return False
        # Step 4
        return result
dataset/ETHPy150Open cloudera/hue/desktop/core/ext-py/pycrypto-2.6.1/lib/Crypto/Signature/PKCS1_PSS.py/PSS_SigScheme.verify