Thread: Nuvi 58LMT "can't unlock maps".

I got warnings downloading, extracting and opening JM until I disabled them.

It's part of my curiosity when I see a file like .unl to wonder how the information is encoded rather than just use a tool to parse/generate it and if I can do anything interesting by setting fields to strange values. If it was used as (admittedly bad) copy protection it wont be trivial but not too complex. There are obviously random elements in there as putting the same info in can produce multiple completely different outputs and changing one field changes the whole string. InfoUC looks like it's written in some flavour or BASIC and there's a CRC table in there.

BTW you're sort of right about my formal stuff. I was involved with some rather significant code development before I retired. I somehow persuaded people to pay me to write C code for nearly 20 years with occasional bits of other languages notably perl. Now I do that for fun.

Update: looks like .unl format is a very simple obfuscation which barely counts as cryptography. For my own amusement I'm working on a simple perl script that can unpick it. If I get bored I'll see if I can write something to generate it too.

Update#2: I've wrote a simple perl script that prints out the fields. InfoUC was very helpful in working out the format. Not sure I should say too much about what I found out in a public forum so