Sunday 25 July 2021

Bluefly IGC Validation

This article has been updated for clarity in May 2023.

Six weeks ago I released a new model of the Bluefly with onboard GPS and IGC recording. The BlueFlyVario_Bluetooth_GPS_IGC_v12.3 has been more popular than I first thought. Today I am pleased to announce the BlueFly IGC files can be validated with GpsDump (Version 5.40), so you can use it as a backup for competitions that require validated IGC files. 

What is IGC File Signing?

It would be possible for a pilot to create a fake IGC file for competitions or records. Signing the file with a G-Record is designed to prevent this. The G-Record is a few lines of text at the end of the file that can be used to check if the rest of the file was generated by the device creating the IGC file. Nothing is 100% secure, but the signing mechansim prevents casual tampering except by really determined highly technical hackers. Of course, faking an IGC file would be silly, but some people worry about it. 

The original IGC spec by the FAI requires a pretty sophisticated mechanism for signing IGC files, based on individual device serial number and public key encryption. Some high end devices implement this spec, but they are pretty much limited to use on sailplanes. 

A more relaxed version of the specification is produced by FAI CIVL for Hang Gliding and Paragliding use. This is what has now been implemented on the Bluefly and this new model has been submitted for approval by CIVL. In addition, the developer of GPSDump has implemented Bluefly IGC download and resigning and that can be used right now for uploading your IGC files to online competitions.

You can read a lot more about IGC files and CIVL here

What is IGC File Validation?

In simple terms this is the opposite of IGC File Signing. A program checks that the IGC file contents match the signature at the end of the file, and that the signature was generated by the device manufacturer. 

GpsDump and the Bluefly (XGD)

GpsDump is one of the most widely used programs for downloading IGC files from flight instruments. Stein has been very kind to implement the Bluefly IGC download protocol and validate the Bluefly G-Record. Once the validated track data is in GpsDump it can then be saved as a GpsDump signed IGC file, which is widely supported by competitions and online validators. After you have your Bluefly successfully installed as a COM port, the first step is to read the list of files from the Bluefly. 

The list of IGC files on the Bluefly is then like this. Note that the duration is approximate only. 

Once the file is downloaded you can then 'Save IGC file made by GpsDump' and add a few details if you like. The GpsDump saved file is re-signed and can then be used by any competition that uses GpsDump files, which I think is almost all of them. 

Bluefly Validation (VBF)

The G-Record signing in the Bluefly can also be used to directly validate the files you have downloaded using the BFVDesktop application. See the release blog post for information on how to download the files directly. The IGC files on the Bluefly use the three letter code VBF in anticipation of this code being compliant with the specification (this may change to XBF in the future). 

To validate files from the Bluefly that you have downloaded directly using the BFVDesktop application you will need the validation program vali-vbf.exe. Use it from the command line like:

>vali-vbf.exe filename.igc

Please note that you will need firmware version 12.529 or later on your BlueFlyVario_Bluetooth_GPS_IGC for the Bluefly IGC validation to work. There were only a few copies of this new model sent out with an earlier version of the firmware. If you do not have 12.529 or later please contact me and I will help you update it.