The IGC-files of SkyLoggerXXL contain a digital signature that allow checking of the authenticity of the IGC-files.Therefore, IGC-files cannot be changed undetected.
The digital signature is stored in the so called G-Record of the IGC-file. The algorithm for creating the signature is secret. The algorithm for checking the authenticity of the IGC-file is not published either, although even the knowledge of the algorithm does not allow an undetected change of data.
The published validation programs are using the signature to check the authenticity of IGC-files produced by SkyLoggerXXL. The programs for Linux and Windows are command based programs (they have to be started from a console) while the macOS program has a graphical user interface.
In case the IGC-file passed the checking "ok" otherwise "failed" is output. The return value of the validation program is zero if the file has been validated, otherwise -1 is returned.