inextea

The inextea library provides a small single block XTEA encryptor and decryptor library with optional control of the number of Feistel rounds. The library can be used to encrypt small (8-byte) payloads such as customer IDs and similar.

Note that XTEA is not a particularly strong encryption algorithm due to the small key length. This library also does not support facilities, such as cipher-block chaining, needed to properly encrypt larger payloads. For this reason, this library should not be used for general encryption applications.

The library includes two additional functions used to lightly encrypt customer IDs and other 32-bit values into 8-byte sequences, including a simple checksum. These functions allow you to quickly encode integer values into opaque sequences that are checksum'd and won't leak information such as the number of subscribers.

The library was developed so that we could guarantee the use of the exact same implementation of the xtea encryption algorithm with both C++ and Python code.

Note that the inecrypto <https://github.com/inesonic/inecrypto> library provides another implementation of the XTEA encryptor that can support arbitrary block sizes. The inecrypto <https://github.com/inesonic/inecrypto> also includes a Qt wrapper for the tiny-AES library with support for CBC.

The library was originally developed for the now defunct SpeedSentry site monitoring system that was supported and sold by Inesonic, LLC <https://inesonic.com>.

Python Extension Module

This small library includes a Python extension module you can use to perform the XTEA encryption and decryption. The Python extension module provides four functions:

inextea.decrypt(block, key, number_rounds)

You can use this function to perform a specified number of reversed Feistel rounds on a block.

Parameter	Function
block	The block to perform the Feistel rounds on. Each block must be exactly 8 bytes in length.
key	The Feistel key to be applied. The key must be exactly 16 bytes in length.
number_rounds	The number of Feistel rounds to be performed.

The function returns a bytes object holding the decrypted block.

inextea.encrypt(block, key, number_rounds)

You can use this function to perform a specified number of Feistel rounds on a block.

Parameter	Function
block	The block to perform the Feistel rounds on. Each block must be exactly 8 bytes in length.
key	The Feistel key to be applied. The key must be exactly 16 bytes in length.
number_rounds	The number of Feistel rounds to be performed.

The function returns a bytes object holding the encrypted block.

inextea.to_customer_id(customer_identifier, key)

You can use this function to convert a customer identifier generated by to_customer_identifier back to a 32-bit non-zero unsigned integer.

Parameter	Description
customer_identifier	The 8-byte long customer identifier to be converted.
key	The Feistel key to be applied. The key must be exactly 16 bytes in length.

The function returns a 32-bit integer customer ID value or 0 if the supplied customer identifier is invalid.

inextea.to_customer_identifier(customer_id, key)

You can use this function to convert a 32-bit integer customer ID to an 8-byte customer identifier.

Parameter	Description
customer_id	The integer customer ID to be converted to a customer identifier.
key	The Feistel key to be applied. The key must be exactly 16 bytes in length.

The function returns a byte array holding the 8-byte long customer identifier.

Building inextea

The build environment currently supports both qmake and cmake build tools. You will need to install the Python 3 headers.

qmake

To build inextea and the inextea Python extension library using qmake:

cd inecontainer
mkdir build
cd build
qmake ../inextea.pro
make

If you wish to create a debug build, change the qmake line to:

qmake ../inextea.pro CONFIG+=debug
make

Note that the qmake build environment currently does not have an install target defined.

You may need to modify inextea.pro to point to the correct location for the Python headers and shared libraries.

cmake

To build inextea using cmake:

cd inextea
mkdir build
cmake -B. -H.. -DCMAKE_INSTALL_PREFIX=/usr/local/
make

The cmake build environment will install the inextea static library but will not install the inextea Python extension library. You will need to install that library into an appropriate location manually.

Licensing

This library is released under the MIT license.