Scrambling Algorithm
The controller RDLxxx and the software RDCAM scramble the data when communicating. The same scrambling algorithm is also used for data files (*.rd) of RDCAM.
The scrambling is done block-wise using a block length of 1 byte. Therefore, a simple 256 entry look-up table could be used for both scrambling and descrambling. However, it is possible to describe the scrambling using elementary logic operations, which allows for faster and shorter implementation. This page describes the simple scrambling and descrambling procedures. Please note that different versions of the controller and the RDCAM software use slightly different values in the scrambling procedures.
Scrambling
| Step | Description | C Code |
|---|---|---|
| Input | a descrambled/plain byte p (0x00 ... 0xFF) | uint8_t scramble(uint8_t p) { |
| 1 | swap first and last bit | uint8_t a = p & 0x7E | p >> 7 & 0x01 | p << 7 & 0x80; |
| 2 | bit-wise exclusive OR with magic number | uint8_t b = a ^ MAGIC; |
| 3 | add 1 with wrap-around | uint8_t s = (b + 1) & 0xFF; |
| Output | a scrambled byte s (0x00 ... 0xFF) | return s; } |
Descrambling
| Step | Description | C Code |
|---|---|---|
| Input | a scrambled byte s (0x00 ... 0xFF) | uint8_t descramble(uint8_t s) { |
| 1 | subtract 1 with wrap-around | uint8_t a = (s + 0xFF) & 0xFF; |
| 2 | bit-wise exclusive OR with magic number | uint8_t b = a ^ MAGIC; |
| 3 | swap first and last bit | uint8_t p = b & 0x7E | b >> 7 & 0x01 | b << 7 & 0x80; |
| Output | a descrambled/plain byte p (0x00 ... 0xFF) | return p; } |
Magic Values
| Controller | RDCAM version | Magic Value | C Code |
|---|---|---|---|
| RDL9635 | 3 | 0x38 | #define MAGIC 0x38 |
| RDLC230-A | 6 | 0x88 | #define MAGIC 0x88 |
| RDC6442G | 8 | 0x88 | #define MAGIC 0x88 |
Disclaimer
Please note that all information is to the best of my knowlege, but you may only use it at your own risk. All information is provided without warranty of any kind. The provided information is to be used for educational purposes only.