Tag Archives: OTP

OTP Authentication required to unlock IMS Debugging and TCPDUMP on Samsung Sysdump tool

Reverse Engineering Samsung Sysdump Utils to Unlock IMS Debug & TCPdump on Samsung Phones

Note: This post is just about the how I reverse engineered the tool, for info on how to use it, you want this post.

While poking around the development and debugging features on Samsung handsets I found the ability to run IMS Debugging directly from the handset.

Alas, the option is only available in the commercial version, it’s just there for carriers, and requires a One Time Password to unlock.

OTP Authentication required to unlock IMS Debugging and TCPDUMP on Samsung Sysdump tool "This menu is not allowed for commercial version. You can activate this menu after OTP Authentication enabled"

When tapping on the option a challenge is generated with a key.

Interestingly I noticed that the key changes each time and can reject you even in aeroplane mode, suggesting the authentication happens client side.

This left me thinking – If the authentication happens client side, then the App has to know what the valid password for the key shown is…

Some research revealed you can pull APKs off an Android phone, so I downloaded a utility called “APK Extractor” from the Play store, and used it to extract the Samsung Sysdump utility.

So now I was armed with the APK on my local machine, the next step was to see if I could decompile the APK back into source code.

Some Googling found me an online APK decompiler, which I fed the compiled APK file and got back the source code.

I did some poking around inside the source code, and then I found an interesting directory:

Here’s a screenshot of the vanilla code that came out of the app.

Samsung OTPSecurty Source Code

I’m not a Java expert, but even I could see the “CheckOTP” function and understand that that’s what validates the One Time Passwords.

The while loop threw me a little – until I read through the rest of the code; the “key” in the popup box is actually a text string representing the current UNIX timestamp down to the minute level. The correct password is an operation done on the “key”, however the CheckOTP function doesn’t know the challenge key, but has the current time, so generates a challenge key for each timestamp back a few minutes and a few minutes into the future.

I modified the code slightly to allow me to enter the presented “key” and get the correct password back. It’s worth noting you need to act quickly, enter the “key” and enter the response within a minute or so.

In the end I’ve posted the code on an online Java compiler,

Generate OTP Response from Key (Challenge)

Replace yy182 with your challenge. I suggest you try the 0 offset and type it in quickly.

I did a write up on how to use the features this unlocks in this post.

If you’re leaning about VoLTE & IMS networks, or building your own, I’d suggest checking out my other posts on the topic.


VoLTE/IMS Debugging on Samsung Handsets using Sysdump & Samsung IMS Logger

Samsung handsets have a feature built in to allow debugging from the handset, called Sysdump.

Entering *#9900# from the Dialing Screen will bring up the Sysdump App, from here you can dump logs from the device, and run a variety of debugging procedures.

Samsung share information about this app publicly on their website,

Sysdump App in Samsung handsets used for debugging the device

But for private LTE operators, the two most interesting options are by far the TCPDUMP START option and IMS Logger, but both are grayed out.

Tapping on them asks for a one-time password and has a challenge key.

OTP Authentication required to unlock IMS Debugging and TCPDUMP on Samsung Sysdump tool

These options are not available in the commercial version of the OS and need to be unlocked with a one time key generated by a tool Samsung for unlocking engineering firmware on handsets.

Luckily this authentication happens client side, which means we can work out the password it’s expecting.

For those interested I’ve done a write up of how I reversed the password validation algorithm to take the key given in the OTP challenge and generate a valid response.

For those who just want to unlock these features you can click here to run the tool that generates the response.

Once you’ve entered the code and successfully unlocked the IMS Debugging tool there’s a few really cool features in the hamburger menu in the top right.

DM View

This shows the SIP / IMS Messaging and the current signal strength parameters (used to determine which RAN type to use (Ie falling back from VoLTE to UMTS / Circuit Switched when the LTE signal strength drops).

Screenshot of Samsung Sysdump tool in the IMS Debug - DM View section

Tapping on the SIP messages expands them and allows you to see the contents of the SIP messages.

Viewing SIP Messaging directly from the handset

Interesting the actual nitty-gritty parameters in the SIP headers are missing, replaced with X for anything “private” or identifiable.

Luckily all this info can be found in the Pcap.

The DM View is great for getting a quick look at what’s going on, on the mobile device itself, without needing a PC.


The real power comes in the logging functions,

There’s a lot of logging options, including screen recording, TCPdump (as in Packet Captures) and Syslog logging.

From the hamburger menu we can select the logging parameters we want to change.

Settings for Samsung IMS Logger

From the Filter Options menu we can set what info we’re going to log,

Filter options used in Dump output of Samsung IMS Logger application

If you’re leaning about VoLTE & IMS networks, or building your own, I’d suggest checking out my other posts on the topic.