[Samsung Galaxy Nexus] jup007:
This theory now seems to be confirmed by number of successful applications & my additional research. It should be generally safe to try both experiments. However, it still requires you know basics of shell. Above all, backup. And as allways, I am not responsible for anything, I don't even exist, etc...

And if you test this, please provide feedback.

This post will be updated as needed. For update list see the end.

What you need

Rooted GNEX with perm unlock & generic IMEI by ****Docomo app from this thread: http://xdaforums.com/showthread.php?t=1548210. If you bought Docomo device from Negri, you already have this "patch" applied & just need root.

4.0.4 based ROM, yakju and takju builds are tested. Feel free to try different versions but we know that 4.0.3 is different.

Some form of shell access to your device

Busybox helps, but is not really needed.

The basic theory of permanently unlocking gnex w/ IMEI intact

Theorems

lock status and your IMEI are contained in nv_data.bin files on gnex.

there are usually three nv_data.bin file: /factory/.nv_data.bak, /factory/nv_data.bin, /data/radio/nv_data.bin. The one in /data/radio is the one really used under normal operation, but the least important one. In some way, it gets updated during every boot (boot counter?) and if you destroy it, it will get replaced from /factory ones (I am not sure which one is preferred).

all of these files are signed and signature is in accompanying files with .md5 sum.

unfortunately, it's not clean md5, there is some seed added to it, so nobody knows how to generate them correctly.

From these follows

It would appear that on Galaxy S 2 and other phones you could get around SIM lock simply by editing nv_data.bin files. There are well known locations where one can find unlock status and some additional data and basically unlocking consists of resetting byte at 0x181469 with 0 (contains 1) and replacing about 30 bytes before that with 0xff. If you did this for /data/radio/, you'd get temp unlock, if you replaced files in /factory, you'd get permanently unlocked phone. Easy.

This also (partially) worked on 4.0.3 ICS for files in /data/radio, however /factory files are now protected by md5 checksum with unknown seed. Since 4.0.4 this md5 protection was extended to /data files. THIS IS UNCONFIRMED AS OF NOW.

md5 protection makes it impossible to tamper with those files unless one has a way to generate correct checksum. When system encounters files that have incorrect checksum, it will simply ignore them.

****DocomoV2 perm unlock correctly replaces nv_data.bin files with their unlocked versions (hex manipulation above) but where it fails is generating correct md5 files. Hence all the nv_data.bin files get ignored outright and gnex falls back to some nv_data.bin with generic IMEI that is obviously last resort and probably meant for developers. So unlock only works as side effect. On further reboots, /data/radio/nv_data.bin is correctly checksumed, so it's used, but it contains generic IMEI. On wipe, it's regenerated from fallback again.

If you have phone from negri that has permanent lock applied, you don't even have backup of your original DOCOMO locked nv_data.bin files. This may not be

true for all versions, but it's true for recent shipments from negri with ICS

4.0.4 and can be confirmed by checking byte 0x181469 at all three nv_data.bin

files. It will be 0x00 == unlocked. However, except for unlocking them, ****Docomo didn't do any damage to them, it just rendered them invalid from samsung point of view - checksums don't match.

So if we have way how to generate correct md5 files matching these, we will get unlocked phone with real IMEI. And thanks to little oversight on Samsung part, we do. This oversight is called log files.

Following tests assume that you have phone with permanent unlock of ****Docomo applied. Ie you have phone from Negri with generic IMEI.

1. Theory test (reasonably SAFE)

It's probably better to have phone in airplane mode for these tests. I did for some, didn't for others. But it may overwrite /data/radio if you don't. Switch it off only after reboot.

Log into your phone. su to root. I use adb shell, but any shell will work as

long as you can get root privileges.

$ su
# cd /data/radio/log
# cat nv.log

Check that it contains lines like this example (2 different at least):

Tue Apr 17 11:33:47 2012: MD5 fail. orignal md5 '24989da14a3ad550546d2d23254c8f03' computed md5 'adaa0bf9506d939d18d57f96c0c330a3' (rild)

hashes will obviously differ for each gnex. If you can't see these, you could try wiping /data/radio/nv_* (2 files) and rebooting. This will attempt to regenerate files from factory files. If then you still don't see lines, then either your phone hasn't been tampered with or my theory is incorrect. Let me know.

# cat /factory/nv_data.bin.md5

this will output another md5 hash. Try to find it in above log in column original md5. It should be there. If it is, congratulations, you have correctly f*&^%ed device. The line tells us that md5sum in the aforementioned md5 file is invalid. It also tells us what valid md5 should be! How kind of Samsung. Let's correct this "glitch". Copy somewhere the part in apostrophes after computed md5 on the SAME line that contains hash from above md5 under original md5 (32 characters, for example, if cat outputs 24989da14a3ad550546d2d23254c8f03, it will be adaa0bf9506d939d18d57f96c0c330a3 for above line). I will call it COMPUTED.

# cd /data/radio
# rm nv_data.bin nv_data.bin.md5
# busybox cp /factory/nv_data.bin .
# echo COMPUTED > nv_data.bin.md5
# chown radio.radio nv_data.bin*
# chmod 700 nv_data.bin*

So we're copying original file from /factory to /data/radio and creating brand new md5 file that contains hash matching this nv_data.bin.

# reboot

If you did everything correctly, you end up with your original IMEI after reboot. If you destroyed something in /data/radio, don't worry. The files in /data/radio will be regenerated if md5 sum doesn't match or if you delete them, you'll just end up with generic IMEI. Check the log file and try to figure out what happend. If it says default NV restored at the end with current timestamp, well, default NV is the generic one. If you end up with completely wiped IMEI, that usually means permissions of the files in /data/radio are incorect. If above procedure worked, no lines should be added to it, because /data/radio/nv_data.bin was correct.

Mention that we're only touching /data/radio/. This is mostly to prove theory. This file WILL get wiped on factory reset and you'll end up with generic IMEI again. So we just recreated, painfully, temp unlock of ****Docomo app, except that this version works for 4.0.4. But this is side effect just to prove the theory. The real goodie comes now:

2. Theory application (do at your OWN RISK)

You know what's coming anyway. You're smart guys. But first:

BACKUP your /factory off the device

BACKUP your /factory to the cloud

the best thing is to use tar from busybox (preserves file permissions), you can probably use recovery ROMs etc. Just make the good backup. If you damage your /factory/, you may screw your device and never get GSM access again unless paying somebody with SPTBox. There's NO SAFEGUARD unlike when you modify /data/radio. NONE. I hope you got it.

Remount /factory rw. I used root explorer, you can use command line, but you need write access. Do not touch nv_data.bin or .nv_data.bak files. They've been already fixed by ****Docomo and you really NEED them, so please, don't delete them. Also, remember that files starting with dot are treated as hidden by linux, meaning if you want to see them in output of ls, you need to use -a argument.

Now we just need to fix md5 sums. So do as above for data. Find matching lines in nv.log by original md5 and correct md5 sum in computed md5 part and

$ su
# cd /factory
# echo COMPUTED > nv_data.bin.md5
# chown radio.radio nv_data.bin.md5
# chmod 700 nv_data.bin.md5

# echo COMPUTED2 > .nv_data.bak.md5
# chown radio.radio .nv_data.bak.md5
# chmod 700 .nv_data.bak.md5

So yes, COMPUTED is the same as for /data/radio (it matches nv_data.bin), COMPUTED2 is different (and matches .nv_data.bak).

Remount /factory R/O (probably not needed, but it should sync it so recommended).

Wipe /data/radio/nv_* (2 files):

# cd /data/radio
# rm nv_data.bin nv_data.bin.md5

This is strictly speaking redundant, if you did the theory test before, since you already have correct files there. However, it will verify that everything is fine and it simulates what happens during factory reset. So wipe them.

# reboot

... and hope for the best. If you have original IMEI after that, you're probably unlocked forever and may forget about terminals. Try factory reset if you want, flash roms, your gnex is liberated. Go get a beer, it's worth it. If something broke, chances are you're back on generic imei, in which case, nv.log is your friend. And let me know.

Notes

it would be probably better to use "echo -n" instead of "echo", somone could give it try, but I used "echo" myself and it works. However, md5 sums have redundant newline at the end.

I am quite sure this will stop working on future firmwares. This is a loophole that will be closed once people at Samsung mention it (and I am pretty sure they monitor these forums, uhm, hello there). However, I believe that once you have complete set (nv_data.bin & matching md5 files), you're basically not distinguishable from stock sim unlocked phone, so you should be safe there. There's no 100% guarantee though - they are the guys that know their hardware inside out.

Backup /factory if everything works. SEPARATELY from previous backup. This may come handy in future as it contains /factory files matching unlocked version of you phone, so if you loose it, you can use it again.

If you run ****Docomo yourself, you might also want to backup /sdcard/.unlock_backup (or where ****Docomo creates its backup) or better yet, backup /factory off device before running ****Docomo. We, with Negri phones, don't have this luxury.

DISCLAIMER: I don't think this method can be used to spoof IMEI and that's a good thing. Some people claim they know how to change IMEI in nv_data.bin, but I am quite sure there are other security measures to protect it. So this can only return you your old IMEI. Which is good thing in my books (and probably evil in Samsung's, although they're just playing by carrier's tune here)

If this theory is confirmed, someone should write an app. It can be automated with grep or sed.

Updates:

Changed slightly commands in theory test to make sure that nv_data.bin has correct permissons. If it doesn't, you'll end up with wiped up IMEI (which is not really problem, this can be fixed, but you won't be able to get GSM connection until then) -- thanks cpxchewy for this

4/20 - Added Docomo to title, changed intro to reflect successful tests

4/26 - Added info about takju test.

4/27 - mention that files with dot are hidden