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GLIDER ANTI-COLLISION RADIO PROTOCOL VERSION 6 (2015)
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courtesy of unknown

Document Release: 0.0

For background information read document from 2008:

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PROTOCOL VERSION 4 (2008)
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courtesy of Hiram Yaeger

NEW ENCRYPTION

Swiss glider anti-colission system moved to a new encryption scheme: XXTEA
The algorithm encrypts all the packet after the header: total 20 bytes or 5 long int words of data

XXTEA description and code are found here: http://en.wikipedia.org/wiki/XXTEA
The system uses 6 iterations of the main loop.

The system version 6 sends two type of packets: position and ... some unknown data
The difference is made by bit 0 of byte 3 of the packet: for position data this bit is zero.

For position data the key used depends on the time and transmitting device address.
The key is as well obscured by a weird algorithm.
The code to generate the key is:

void make_key(long *key, long time, long address)
{ const long table[4] = { 0xe43276df, 0xdca83759, 0x9802b8ac, 0x4675a56b } ;
  for(int i=0; i<4; i++)
  { key[i] = obscure(table[i] ^ ((time>>6) ^ address), 0x045D9F3B) ^ 0x87B562F4; }
}

long ObscureKey(long key, unsigned long seed)
   { unsigned long m1 = seed * (key ^ (key>>16));
     unsigned long m2 = seed * (m1  ^ (m1>>16));
     return m2 ^ (m2>>16); }


NEW PACKET FORMAT:

Byte     Bits
 0     AAAA AAAA    device address
 1     AAAA AAAA
 2     AAAA AAAA
 3     00aa 0000    aa = 10 or 01

 4     vvvv vvvv    vertical speed
 5     xxxx xxvv
 6     gggg gggg    GPS status
 7     tttt gggg    plane type

 8     LLLL LLLL    Latitude
 9     LLLL LLLL
10     aaaa aLLL
11     aaaa aaaa    Altitude

12     NNNN NNNN    Longitude
13     NNNN NNNN
14     xxxx NNNN
15     FFxx xxxx    multiplying factor

16     SSSS SSSS    as in version 4
17     ssss ssss
18     KKKK KKKK
19     kkkk kkkk

20     EEEE EEEE
21     eeee eeee
22     PPPP PPPP
24     pppp pppp