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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 _build_encryption_key(self, subtitle_id, key_size=ENCRYPTION_KEY_SIZE):
 """Generate the encryption key for a given media item Encryption key is basically just sha1(<magic value based on subtitle_id> + '"#$&).6CXzPHw=2N_+isZK') then padded with 0s to 32 chars @param int subtitle_id @param int key_size @return str """


        # generate a 160-bit SHA1 hash
        sha1_hash = hashlib.new('sha1', self._build_hash_secret((1, 2)) +
            self._build_hash_magic(subtitle_id)).digest()
        # pad to 256-bit hash for 32 byte key
        sha1_hash += '\x00' * max(key_size - len(sha1_hash), 0)
        return sha1_hash[:key_size]