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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def step2(self, pub_key, salt):
 """Second authentication step."""

        self._check_initialized()
        pk_str = binascii.hexlify(pub_key).decode()
        salt = binascii.hexlify(salt).decode()
        self.client_session_key, _, _ = self.session.process(pk_str, salt)
        _LOGGER.debug('Client session key: %s', self.client_session_key)

        # Generate client public and session key proof.
        client_public = self.session.public
        client_session_key_proof = self.session.key_proof
        _LOGGER.debug('Client public: %s, proof: %s',
                      client_public, client_session_key_proof)

        if not self.session.verify_proof(self.session.key_proof_hash):
            raise AuthenticationError('proofs do not match (mitm?)')
        return client_public, client_session_key_proof