75ZT Community

Duncan · Posted 31 May 2011, 20:41 #1

This may seem the wrong place for this question, but it's related to the cars, so I'll put it here.

Does anyone have a ood working knowledge of checksum calculation? I'm trying to reverse engineer one (not ZCS codes but similar) and never studied it in any detail.

The scheme used takes a number of hex digits, and provides a check character in alphanumeric form, which apparently includes some special characters as well as 0-9 and A-Z.

Anyone have any ideas?

Bernard · Posted 01 Jun 2011, 09:13 #2

I doubt that I have kept any notes from 30 years back but I don't remember special characters being involved in what we were doing at the time.
Unless the special characters are ASCII type representations of two bit Hex codes, 0-FF?
In which case it may be a simple sum of the characters represented in the string being checked but printed out as ASCII.

Duncan · Posted 02 Jun 2011, 11:37 #3

Thanks, I think I've figured it out now.

Does anyone have any barcodes for keys around, and would be willing to check out my theory? If so, they could either PM me the first 6 characters after the N on the first line and I'll respond with what should be the complete thing, or if willing, PM me the whole thing to check against my theory. It's worked for the two barcodes I have so far.

Duncan · Posted 02 Jun 2011, 12:29 #4

Update: no urgency, I seem to have verified it myself by aligning a third keyfob that I don't have a barcode for. :mrgreen:

Mick · Posted 02 Jun 2011, 12:31 #5

I have one in front of me if you still need it

Duncan · Posted 02 Jun 2011, 13:07 #6

You have a PM!

Mick · Posted 02 Jun 2011, 13:29 #7

You have a reply.

Duncan · Posted 02 Jun 2011, 13:41 #8

Well, another confirmed then, excellent. That confirms I can now recreate the barcode strings from data on the PCB (Printed Circuit Board) inside the key (so long as they haven't had the label removed).

Duncan · Posted 02 Jun 2011, 13:55 #9

Just been going through it again, and still need one more example, a very particular case.

If anyone has one where the first line of the barcode starts like this:

*Nxxxxx0

where x is any value, but the sixth value after the N is 0, I could do with doing the check.

solo.cab · Posted 02 Nov 2011, 22:38 #10

N3B1280
IS THAT WHAT YOU NEED
MAL

Duncan · Posted 03 Nov 2011, 07:55 #11

Yes thanks.

I'll get the calculator out and come back to you.

Thanks

Trebor · Posted 05 Nov 2011, 19:51 #12

if you can guarantee it will work on Christine Duncan, then consider it cracked

Duncan · Posted 06 Nov 2011, 17:53 #13

Thanks Mal, for confirming the operation with a code ending in zero. It does work the most logical way it might have, but sometimes these things don't.

Duncan · Posted 06 Nov 2011, 17:54 #14

Trebor wrote:if you can guarantee it will work on Christine Duncan, then consider it cracked

Nothing is ever guaranteed with Christine. Except trouble.......

solo.cab · Posted 06 Nov 2011, 22:13 #15

No problem anytime, did you see poppy's goodbye on other side,things are a bit weird.
Mal

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Anyone know about checksums? by Duncan