Bypass signature requirement for COD files

July 31, 2007

Actually it didn’t work as we had expected. We still cannot bypass signature control, but results, in fact, quite interesting.

After many unsuccessful experiments and reviews of both – SignatureTool and rapc , we decided to try another approach – net_rim_api. Our assumption was that any API call should be mapped to particular function prototype in net_rim_api library. If we can learn how it was done then the next step would be to create our own “prototypes” of system functions and try to bypass needs for application signing. Our assumption was “almost” correct. Why “almost” I’ll explain later.

What we did, we used information dumped from cod files, namely – class names and methods definitions, to create prototype java files. An example:

// ##########################################
// Decompiled by : coddec
// Module : XXXXXXXXXXXXXX.cod
// Module version : 4.2.1.89
// #########################################
package net.rim.vm;

public class Process
{

native public int getLastIdleCounter();
}

The trick is just simple to declare a function as native. Then the file was compiled using standard java compilator. The resulting class file was slightly corrected by JavaBite tool to remove constructor code, but I am not quite sure that it was strictly required. Anyway you are free to experiment.

Next step is to add our class file to ne_rim_api.jar file. This task is very-very simple. We used 7-Zip to accomplish that.

Well, that’s it. If in your project you call getLastIdleCounter(), rapc will compile your project without any signature warning. Why was it cool ? getLastIdleCounter() is just an example, using the same approach is possible to call system functions not using protected RIM API.

Unfortunately, it only worked on emulator. There was additional signature requirement we weren’t aware of. Signer ID for this one is 33 and it appears as “Secure API” in the error message. We couldn’t find any useful information regarding that, but it seems it is related to so called “Secure Device” flag and it works the same way as firewall rule – “Deny All”.

If it would be possible to turn the flag off … We are trying to figure out how …

By the way, the public key for Signer ID ( 33 ) is the same for all devices and BB emulator, it begins with 0x8F A7 61 CA 6E B6 94 5E 28 86 … the length is 128 bytes (1024 bits). It is physically located in rim*.sif file.

Another possibility would be replace this key with own public key, but it would be necessary to re-sign all system libraries using own private key as well. And we are not quite sure if it would be possible to patch sfi file at all as it might be signed too.


History of COD format

July 31, 2007

For those interested in COD format, a patent publication from RIM revealing some ideas behind its creation – 20060020932 .