Nikon Firmware Insights #05

Just to let people know, yes I’ve been working on understanding the D5100 firmware.

I’ve got most the area’s of code identified (where they are, not what they do), but there are some puzzles, with some chunks of code that are used (eg selects a picture to be shown based on shooting mode) but the code it self is not directly linked to, and it’s address in not present in the image. There is defiantly some form of jump/call table compression/encoding done, as there are functions that do some maths, and then call the result. So that needs to be puzzled out.

So to help map the data (and thus remove possible options from above puzzle), I previous mentioned mapping the jpg’s out:

As can be seen in this small sample, there’s the icons for the different shooting modes, and three colour schemes.

Last night I was working on using a modified version of BinViz (original found here) and have found how the font’s and overlay text/images are packed, and I am in the process of tracking down how the width/size information is encoded in the associated data tables. Shown below is the same block of data shown, but at two different widths, showing the “Dial” overlays and the “Bulb Time” text:

It’s quite neat looking at the Asian font sets, as the fonts/overlays use subpixel rendering, which can be seen in the green arm of the sports mode dial icon above. Much simpler, the normal overlays are just black/white, and now look better X/Y scaled.

I started a Google Code Project called Nikon Firmware Tools in which I’m placing the tools I’m using and the changes I’m making to them as I go. So interested developers can look there. Sorry only code so far.

 

Interested in more, come join the us at Nikon Hacker, or use the Online Patch Tool (Help)

Nikon Firmware Insights #04

A little under 24 hours ago, and roos posted he and Kungsholmens Kameraklubb found the checksum for the D7000 A & B firmware , but it didn’t work on the d5100 firmware.

The code they used was the big endian form of the CRC16, but running on little endian CPUs.

Turning the Wikipedia CRC code into C# follows:

For the D7000 A & B, D300S A&B, D3S A & B, D3100 A, D5100 A firmware files use start: 0x0000, mask=0x1021

For all models (D3S, D300S, D7000, D5100 & D3100) the CRC is a normal Xmodem CRC16, the originally reported difference for D5100 & D3100 was due to a XOR error (by me), that is now found & fixed.

static int crcBig(byte[] data, int len)
{
    int rem = 0x0;

    for (int i = 0; i < len; i++)
    {
        rem = rem ^ (data[i] << 8);
        for (int j = 0; j < 8; j++)
        {
            if ((rem & 0x8000) != 0)
            {
                rem = (rem << 1) ^ 0x1021;
            }
            else
            {
                rem = rem << 1;

            }
            rem = rem & 0xFFFF; // Trim remainder to 16 bits
        }
    }
    // A popular variant complements rem here
    return rem;
}

For the D5100 B firmware use start= 0x4ed4, mask= 0x1021

D5100 checksum passed, now loading firmware
D5100 HaCkEd firmware running.

The D3100 B firmware also matches the same start value, so I’d assume it’s common to both. And the only thing I modified here was the firmware help message, and I’ve not tested if you can load the 1.01 firmware over top it’s self. That is the next step. Also to make a tool (Vitaliy?) the patches and encrypts for you to avoid typo’s.

[Update]
Very import and good news, firmware lets you flash same version over top it’s self. Thus my camera is now back running normal Nikon 1.01 firmware. Warranty unbroken!
[Update 2: 27 Nov] Fixed CRC code in light of XOR code change.

Interested in more, come join the us at Nikon Hacker, or use the Online Patch Tool (Help)

Donate Button Removed

Yesterday after a couple of suggestions, I added a PayPal donate button, I thought I’d done it correctly, but it appears it didn’t work.

I also said I would be happy to accept money in order to pay for a legit version of IDA Pro. I’ll return the one donation I did get.

I then proceeded to have many emails with Vitaliy about how the work could be done with the free version. While his methods will technically work, I’m just not sure I want to publicly endorse them.

So to avoid offending ‘the scene’ with personal greed, I’m pulling my hat from the race. I’ll just be the guy that solved the encryption and stick with that.

Interested in more, come join the us at Nikon Hacker, or use the Online Patch Tool (Help)

Nikon Firmware Insights #03

The B firmware is were the major action is, and it’s based on the Fujitsu FR chipset. This seems to be the same chip as used by the earlier Nikon DSLRs and the Pentax cameras.

Looking at the B firmware you can see text, for example English @ 0x5ACC68 to but the table of addresses prior to this text block have the same relative spacing of values but are 0x40000 bytes higher in value.

Browsing elsewhere in the file, shows this pattern holds up for the entire file. You can check by finding some text, ad 0x40000 to the text file address, then search for that resulting hex value, ta-da

So we can assume the code is loaded starting at 0x40000.

Next is what we are going to decode the file with. If you have commercial version of IDA Pro then your in luck as it comes with the Fujitsu FR CPU decoder built in. I only have the free version, so am not so luckly.

Kevin Schoedel however has written a pretty good dissembler for the FR CPU, as part of previous Pentax firmware work. I struggled to get the original code working correctly, so I rewrote it in C# and now understand how to use it, and really appreciate his efforts. But I am left oh-so-much wanting IDA Pro style everything. The worst thing is I almost want to pay the $500USD to have that IDA Pro magic, but if I have that money ‘spare’ why didn’t I just buy the D7000 to start with.

Anyway, my present D5100 B firmware DFR import file looks like:

# File map: D5100
-i 0x00040000-0x00BFFFFF=0x00000000

# Memory map:
-m 0x00040000-0x00040947=CODE
-m 0x00040948-0x000409b3=DATA:L
-m 0x000409b4-0x00050068=CODE

# interupt vector table.
-m 0x000dfc00-0x000dffff=DATA:L

#-m 0x000e0000-0x0x000fffff=DATA:L // this is 0xFF rubbish

-m 0x00100000-0x00236A4A=CODE

and heres my C# port of DFR, to use the above with.

If Ilfak wants to give me a free copy of IDA Pro, or even just the FR processor that works with 5.0, I would be very humbled.

The FR – CM71-00101-5E.pdf instruction manual from Fujitsu is very useful.

Here the first 0x4a bytes of the firmware, you can see the interupt vector table being loaded at 0x4002c.

Disassemble 0x00040000-0x00040947 (file 0x00000000) as CODE

00040000 (00000000)  9F80 5000 0000         LDI:32  #0x50000000,R0
00040006 (00000006)  C011                   LDI:8   #0x01,R1
00040008 (00000008)  1501                   STH     R1,@R0          ; 0x50000000
0004000A (0000000A)  9B00 03E0              LDI:20  #0x003E0,R0
0004000E (0000000E)  9F81 4700 0000         LDI:32  #0x47000000,R1
00040014 (00000014)  1401                   ST      R1,@R0          ; 0x000003E0
00040016 (00000016)  9B00 03E7              LDI:20  #0x003E7,R0
0004001A (0000001A)  C031                   LDI:8   #0x03,R1
0004001C (0000001C)  1601                   STB     R1,@R0          ; 0x000003E7
0004001E (0000001E)  8710                   STILM   #0x10
00040020 (00000020)  9F8F 6800 0800         LDI:32  #0x68000800,R15
00040026 (00000026)  9F80 000D FC00         LDI:32  #0x000DFC00,R0
0004002C (0000002C)  B300                   MOV     R0,TBR
0004002E (0000002E)  9B00 0600              LDI:20  #0x00600,R0
00040032 (00000032)  9B41 0185              LDI:20  #0x40185,R1
00040036 (00000036)  1401                   ST      R1,@R0          ; 0x00000600
00040038 (00000038)  9B00 0640              LDI:20  #0x00640,R0
0004003C (0000003C)  C401                   LDI:8   #0x40,R1
0004003E (0000003E)  1401                   ST      R1,@R0          ; 0x00000640
00040040 (00000040)  9B00 0680              LDI:20  #0x00680,R0
00040044 (00000044)  9F81 799F 9910         LDI:32  #0x799F9910,R1
0004004A (0000004A)  1401                   ST      R1,@R0          ; 0x00000680

The second address in parens is the original file offset to help with looking up the file.

 

Interested in more, come join the us at Nikon Hacker, or use the Online Patch Tool (Help)

Nikon Firmware Insights #02

So once the D5100 1.01 firmware was update was released, I couldn’t help but decrypt it.

As noted in the previous post, the bundle is checksum’ed, but I didn’t mention that each sub-file is also checksum’ed. But you can see the checksum at the end of the files:

Now on some Pentax forum I was reading about people wondering if the checksum was checked. So I altered the help file text for the viewing firmware information to make the ‘c’ of camera upper case.

Now the file is just XOR’d with the larger one time pad discussed earlier, and ‘c’ to ‘C’ is just XOR’ing with 0x20, applying the same XOR to the encrypted file at the same location, will have the net result of making the output upper case.

I put this altered firmware on a SD stick, and popped in into the D5100. Long story short, it recognized the update, but once I started the update, it quit really early in the process. The amount of time I’d expect for the checksum to be checked…

So I then turned to the internet for checksum algorithms, and it doesn’t appear to be a CRC-16-anything, as I brute forced the full possibility space, that was a fun adventure in multi-threading batch processing. Nor does it seam to be a Fletcher’s Checksum.

So now I’m up to searching for the answer in code…

[Update: 25 Nov] Answer found by Roos, see here

 

Interested in more, come join the us at Nikon Hacker, or use the Online Patch Tool (Help)