SRDsh

SRDsh provides a SSH server (Dropbear) and a collection of standard command line utilities (toybox) via a single, standalone cryptex. It is intended to be installed alongside other cryptexi, leveraging the modularity of the cryptex system, as opposed to jamming all your tools, etc. into a single cryptex.

2024 Update: Using multiple cryptexes in tandem has a variety of issues; the original vision I had of maintaining ports of tools for the SRD in multiple different cryptexes didn't really pan out. A notable recent addition is the "user" folder in the apps subdirectory, which provides a place to insert proof-of-concept code, etc. that will automatically be available in PATH as user-app via SSH.

This project is primarily for my own use. I've chosen to make it open source in case other researchers find it useful. Support or active maintenance should not be expected.

Build System

Another goal of this project was an attempt to clean up the build system of the example cryptex provided in the SRD repo, starting with the tools I most frequently use first. Some "features" of SRDsh's build setup compared to the example cryptex are:

• no use of recursive make (outside of building submodules);
• a more correct dependency graph that prevents redundant rebuilds; and
• inclusion of dependencies as submodules instead of auto-fetching tarballs.

You may find the helpers in mk/ and the ideas in the root makefile useful in other projects.

Build

To build, clone the SRDsh repo (with submodules) and run make:

git clone --recurse-submodules [email protected]:jonpalmisc/srdsh.git
make

You will need the Xcode CLI tools installed and cryptexctl available in your path.

To install the cryptex on your device, you can use the install convenience target provided:

make install

Note that you will likely need to set the CRYPTEXCTL_UDID environment variable in your shell for the above command to work.

Usage

Once installed, you should be able to SSH into your device as you'd expect:

ssh root@<device-ip>

License

SRDsh is licensed under the Apache 2.0 license. Portions of SRDsh are based on code from the SRD repo's example cryptex, also licensed under the Apache 2.0 license.