Lately I play a bit with Docker containers. In a chain of problems that I have right now, I needed to have static cURL library on Debian. As it turned out linking cURL statically is not an easy task. Rather it causes a lot of problems, especially when trying this with packages available in Debian repos. After a long fight with these I decided to prepare my own distribution of cURL. But instead of creating usual deb package, I did it all on Docker and as a result, I have Docker image. In it I utilized possibilities of staged builds, where there can be few steps having in common only certain files. As a result I created base image, means the one created from scratch, where there are no other files, than the ones that we provide. So I provided only complete cURL install directory and musl libc to be able to run curl binary, as I did not want to tinker with cURL’s build system even more, than I did. Final image weights only ~1,5 MiB, so a result is really nice space saving compared to usual approach to Docker images. Inside, you can run curl binary separated from your operating system (to extent that Docker provides – remember, it is not virtualization!). Also it is possible to use libcurl to link your own binaries with it, this time completely statically!
As always, sources are on Github and this time there are also ready-to-use images on Docker Hub, so you can pull them directly, without need to build them. All instructions are on both pages and this is nothing unusual for any user of Docker, so I will not repeat myself here.
Few months ago I wrote a tutorial about creating Linux distribution consisting of just busybox as its userspace. In the meantime I worked a bit with docker and it sounded like nice next step in learning docker to automate the process of creating Linux distribution using it. As a result, today I present Linux distribution built with docker and based on my previous tutorial. I called it busy-linux due to it consisting of only busybox at the moment. My plan is to develop it further, most likely for private purposes only, so there might not be much happening in the project, but for sure I want to create dynamically linked variant in the near future, as this is what my use case requires. In the meantime feel free to try it yourself. Continue reading “Creating one-file Linux distribution with docker”→
Today, I would like to show something different, than usual reverse-engineering, that appears on my blog usually. I needed to prepare a Linux distro for myself to be able to run it on my PC. But not the ordinary operating system that we download from webpage, then use fancy graphical installer to select, what we want and where. My goals were very specific. First was to have it custom-compiled. With that in mind there aren’t many choices left (maybe Gentoo?). Second was to not cross 16 MiB boundary. Why exactly that? That’s simple. I have old (15 years old to be precise) SD/MMC card made for Canon of exactly that size. Quick check showed me that this is possible. I tried buildroot and it failed to fulfill second requirement and I decided not to continue, despite the obvious optimizations on kernel modules, I could do. It’s simply too complex for such a simple task. If not buildroot, then let’s go and see how to do such thing from scratch!
The plan
Basically the plan is to have custom Linux distro compiled from scratch. It may sound like something incredibly complex and hard to do. But it’s not. There are just few problems one must learn on how to overcome. The most problematic constraint in my case is, obviously, 16 MiB limit. To not exceed it, I have to use busybox as my userspace. This by the way simplifies distro development significantly. Busybox works the way, that, if linked statically, requires only one, single binary to be able to work correctly. So, to sum up, on software side, we need Linux and busybox. You may wonder, how do I want to boot that system, then? Well. I said I need Linux 🙂 Maybe some people know, some does not, that Linux is itself a boot loader of some kind. At least, when using UEFI and this is what I want to use, it can be loaded directly by UEFI firmware. But that’s another thing to note – I will describe a way to prepare a distro for UEFI – it won’t be as simple as that, for legacy BIOS.
The whole plan will look as follows:
Get compiler
Compile Linux kernel
Compile busybox (statically and stripped!)
Prepare initramfs with whole userspace
Format drive as EFI System Partition
Combine kernel and initramfs into single binary
Optionally sign the binary, in case we want Secure Boot to be enabled
Having a tailored cross compiler is a problem I encountered couple of times in the past. Of course there are solutions to that problem like great crosstool-ng or more complex buildroot. In most cases crosstool-ng (ct-ng) can solve them. But whatever the tool we use, it has always its own drawbacks. For ct-ng these are small number of supported versions of toolchain components and huge dependence of environment, where it is started. The latter is even more problematic, because of the way continuing interrupted build work in ct-ng. Obviously if you want to build in example one compiler for ARM and one for MIPS, both consisting of latest tools, then it is not a problem.
But I have another use case for compiling toolchains. I do some reverse engineering from time to time. Nowadays many products have Linux under the hood and often there is no chance to get any SDK for them. But having ability to build something for the device can help a lot, either to run it there, or link with found tools and run in emulator. But I could also imagine that outside the reverse engineering field there might be a need to get toolchain in exact configuration, which is sadly not available via ct-ng or buildroot. Anyway, in any case where ct-ng or buildroot are not applicable, there is third way – docker. And this is the way I chose. This is how CC Factory appeared. It is docker container that builds gcc cross compiler on first startup and lands you in an container that have working compiler for the platform of your choice. And it does not require big effort to port it for the next architecture, or different tool version, unless the changes between the versions were really significant. Continue reading “Meet CC Factory – a factory for cross compilers”→
Android emulator is really nice way to play with Android’s internals. Unfortunately at least those emulators, which have Play Store preinstalled, also don’t have root access via adb root command. What is more, latest emulators started encrypting userdata partition, even if no lock mechanism is configured and there is no way to undo the encryption from inside the Android.
In this article, I will show how to gain access to emulator’s partitions from outside the emulator.
As wikipedia says oldest halftone image printed in a newspaper back in 1873
Long, long time ago, before prices of inkjet and laser printers fell to levels allowing home users to own and use them, there was a primitive printing technology called dot-matrix. As any technology of the past, it is not competitive anymore. However it still has few advantages and one of them is reliability of these devices. Some time ago I found quite a cheap Oki 3321 printer that has 9 pin head and is capable of printing on A3 paper in portrait orientation. Usual mode of printing for these devices was simple text mode, where you just were writing your text in ASCII (or any weird coding popular in your country of origin) to its parallel port. Fortunately these printers usually had also graphic mode, where you could fully use capabilities of the device.
I already was experimenting some time with my device, so I already know it uses Mazovia variant (with zÅ‚ as single glyph) as its codepage. I was also able to guess how to switch into graphic mode, so in theory I was able to print images for some time. Unfortunately any CUPS drivers I used did not provide acceptable results, so all I could do was to write some support tool myself. Continue reading “Printing pictures like its 1873 using Oki 3321 dot-matrix printer”→
When I have seen CO2 sensor for the first time, it was quite expensive device. Well, if one want to buy consumer device these days, it still could cost a lot. However in the days of cheap Chinese electronics sellers on biggest auction platforms, for makers, situation is quite different now. MH-Z14 is the cheapest CO2 sensor I was able to find. I costs about $19 and comes in few variants: MH-Z14 and MH-Z14A. Also it can measure up to 1000 ppm, up to 2000 ppm or up to 5000 ppm. However the range does not matter in practice, as it is possible to switch between them using UART.
The device interfaces are quite flexible for such a cheap device, as beside mentioned UART port it provides PWM and analog output. However, I was not able to measure valid value using analog and my cheap multimeter. Maybe some more sophisticated equipment is required for that.
I have to make one note here: device I bought is labeled as MH-Z14A and its range is 0-5000 ppm. Other variants might have different features. For mine, there is no UART protocol documentation. Yet, protocol documented under name MH-Z14 works, so be careful. Continue reading “mhz14a – program for managing MH-Z14/MH-Z14A CO2 sensors via UART”→
While tinkering with spy camera, I found one detail that is significantly slowing the process of reverse engineering and debugging the applications, installed on its embedded Linux platform – finding final values of preprocessor directives and sometimes also results of sizeof() operator.
As I am not aware of any existing solution for that problem (I guess there might be some included in one of the more sophisticated IDEs, however I use Vim for development) it is good reason to create one. By the way I used cmake template I published some days ago to bootstrap the project. Continue reading “SADVE – tiny program for computing #define values”→
Few years ago I compiled kernel drivers of cheap USB-to-serial converter for my previous Android phone. It took few years of using new phone, without single custom-compiled kernel module. Now it is time to change it. By the way, I am going to describe what changed and what hacks have to be made to make the process work on stock ROM, provided by Sony.
kernel is the key
First of all, we need kernel. To be precise, kernel sources. Without that, it is really hard to be successful (I don’t want to tell it is impossible, but really hard, believe me). Because Sony is very liberal in terms of cooperation with community, they provide anything required to tinker with the device (obviously together with caution message about warranty loss, but who cares, right? 🙂 ).
First of all, we need to know, which firmware version the device uses. To be found in Android settings, as compilation number, or something like that. For me, it is 23.5.A.0.575. Then, we have to visit Open Devices downloads section and find our firmware. For me, it was a lot of scrolling, as I have no updates available for quite some time. Inside the package, there should be kernel directory, with complete kernel sources. Continue reading “USB to serial converter drivers for Android revisited”→
As we now have working Public Key Infrastructure, we are ready to use it for more than encrypting traffic (which is already encrypted by Tor). We can very easily turn on client verification on our server. This will prevent anybody not having valid certificate issued by us from visiting our hidden webpage – just in case hiding domain name in hidden services version 3 leaks the name somehow (which should not happen anymore in v3). In this part we will issue client certificate (the procedure is almost identical to server certificate), then configure httpd to require client identification and finally configure Firefox to try sending the certificate. Let’s go!
Issuing user certificate
In my case tmp directory emulated client machine and ca is my Cerificate Authority, which issues certificates. We start by creating request on client side, then sign it on CA side.
$mkdir tmp$cd tmp$openssl genrsa -out v3l0c1r4pt0r@gmail.com.key.pem 4096
Generating RSA private key, 4096 bit long modulus
........++
..............................................++
e is 65537 (0x010001)
$openssl req -config ../ca/intermediate/openssl.cnf -key v3l0c1r4pt0r@gmail.com.key.pem -new -sha256 -out v3l0c1r4pt0r@gmail.com.csr.pem
You are about to be asked to enter information that will be incorporated
into your certificate request.
What you are about to enter is what is called a Distinguished Name or a DN.
There are quite a few fields but you can leave some blank
For some fields there will be a default value,
If you enter '.', the field will be left blank.
-----
Country Name (2 letter code) [GB]:PL
State or Province Name [England]:lodzkie
Locality Name []:
Organization Name [Alice Ltd]:r4pt0r Test Systems
Organizational Unit Name []:
Common Name []:v3l0c1r4pt0r@gmail.com
Email Address []:v3l0c1r4pt0r@gmail.com$chmod 400 v3l0c1r4pt0r@gmail.com.*.pem$cp v3l0c1r4pt0r@gmail.com.csr.pem ../ca/intermediate/csr/$cd ../ca$openssl ca -config intermediate/openssl.cnf -extensions usr_cert -days 375 \>-notext -md sha256 -in intermediate/csr/v3l0c1r4pt0r@gmail.com.csr.pem \>-out intermediate/certs/v3l0c1r4pt0r@gmail.com.cert.pem
Using configuration from intermediate/openssl.cnf
Enter pass phrase for /home/r4pt0r/Research/cubie/newtor/ca/intermediate/private/intermediate.key.pem:
Check that the request matches the signature
Signature ok
Certificate Details:
Serial Number: 4097 (0x1001)
Validity
Not Before: Feb 27 17:14:40 2018 GMT
Not After : Mar 9 17:14:40 2019 GMT
Subject:
countryName = PL
stateOrProvinceName = lodzkie
organizationName = r4pt0r Test Systems
commonName = v3l0c1r4pt0r@gmail.com
emailAddress = v3l0c1r4pt0r@gmail.com
X509v3 extensions:
X509v3 Basic Constraints:
CA:FALSE
Netscape Cert Type:
SSL Client, S/MIME
Netscape Comment:
OpenSSL Generated Client Certificate
X509v3 Subject Key Identifier:
ED:24:E6:FF:1D:9B:61:AC:29:66:39:59:FB:5D:77:25:F7:A3:55:47
X509v3 Authority Key Identifier:
keyid:3D:AC:8E:21:79:5A:AD:7B:7C:92:92:65:B7:19:D0:E8:00:0E:50:70
X509v3 Key Usage: critical
Digital Signature, Non Repudiation, Key Encipherment
X509v3 Extended Key Usage:
TLS Web Client Authentication, E-mail Protection
Certificate is to be certified until Mar 9 17:14:40 2019 GMT (375 days)
Sign the certificate? [y/n]:y
1 out of 1 certificate requests certified, commit? [y/n]y
Write out database with 1 new entries
Data Base Updated
$cd ../tmp$cp ../ca/intermediate/certs/v3l0c1r4pt0r@gmail.com.cert.pem ./$openssl pkcs12 -export -inkey v3l0c1r4pt0r@gmail.com.key.pem -in v3l0c1r4pt0r@gmail.com.cert.pem -out v3l0c1r4pt0r@gmail.com.p12
Enter Export Password:
Verifying - Enter Export Password:
Last step was packaging certificate and key into PKCS#12 container. That is for securing key (we can encrypt it with password), and is a form required by Firefox. After creation of .p12 (and verifying it is fine), we can (and SHOULD) delete source files, as they are not protected in any way.
Configuring httpd to require user certificate
To enforce client verification, following lines must be added to virtual host configuration, in our case it might go just after SSL certificate file paths.
SSLVerifyClientrequireSSLVerifyDepth 2
We have to reload httpd for changes to take effect.
Installing certificate to Firefox
At last, to start using newly generated certificate, we should install it to Firefox. The procedure is similar to the one with CA certificate. We need to open Certificate Manager window. Then, instead of going to Authorities, we go to Your Certificates. Then we click on Import and select .p12 file.
Certificate Manager / Your Certificates
If the file has password, Firefox will ask for it and after successfully reading the content. If everything went well, you should see your certificate on the list. Now we can try connecting to our hidden service. We should see the window like this:
Server asks for client’s identity
Finally, after confirmation, you should see your hidden service content. Congrats!
