<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def pkdecrypt(self, conn):
 """Handle decryption using ECDH."""

        for msg in [b'S INQUIRE_MAXLEN 4096', b'INQUIRE CIPHERTEXT']:
            keyring.sendline(conn, msg)

        line = keyring.recvline(conn)
        assert keyring.recvline(conn) == b'END'
        remote_pubkey = parse_ecdh(line)

        identity = self.get_identity(keygrip=self.keygrip)
        ec_point = self.client.ecdh(identity=identity, pubkey=remote_pubkey)
        keyring.sendline(conn, b'D ' + _serialize_point(ec_point))