A patch set and script to download and cross-compile Dropbear SSH server for use on Android with password authentication. As the 64-bit binaries don't seem to work reliably, this project is configured to compile 32-bit binaries using the Android NDK toolchain.
Generated binares will all be PIE (position indepedent executable) binaries as it is required on Android 5 (L/ollipop).
If building for android < 4.1 then before building, issue:
export DISABLE_PIE=1
The process consists of just four parts:
- Specify the version of Dropbear you'd like to download and crosscompile. Open build-android-dropbear.sh and change the value of
VERSIONat the top, which defaults to2018.76 - Build your standalone android toolchain.
See the android developer site for more info: https://developer.android.com/ndk/guides/standalone_toolchain.html - Export your toolchain's location:
export TOOLCHAIN=/path/to/standalone/toolchain
- Run the build script:
./build-dropbear-android.sh
Generated binaries will be outputted to {android dropbear repo directory}/target/arm
Much of the project is pre-configured with sane defaults, but if you'd like to customize the behavior of Dropbear for Android, here are a few tips.
- To change/configure most options, look in and modify the following files as appropriate:
a) default_options.h
b) sysoptions.h
c) config.h
For instance, to change the port Dropbear runs on or to change the default location in which Dropbear tries to generate keys, edit default_options.h and modify the respective values.
Dropbear for Android adds a few special flags to Dropbear:
- A: signifies Android mode and allows for password authentication in the absence of the
crypt()lib - G: allows us to specify the GID dropbear should run as
- U: allows us to specify the UID dropbear should run as
- N: specify the login username for the session
- T: specify the authentication key for the session
A typical usecase would be:
./dropbear -d /path/to/dropbear_dss_host_key -r /path/to/dropbear_rsa_hostkey -p 10022 -P /path/to/dropbear.pid -R -A -N user -C password -U u0_aXX -G u0_aXX
The above command will run the Dropbear server with password authentication enabled for the user 'user' with password 'password' and will attempt to run as u0_aXX and in that group. More information can be found by issuing:
./dropbear --help
Big thanks to mkj who has been maintaining Dropbear:
https://github.com/mkj/dropbear
Thanks to NHellfire who's work made the process of getting 2018.76 up and running much easier:
https://github.com/NHellFire/dropbear-android
Thanks to jmfoy for the config.sub and config.guess files:
https://github.com/jfmoy/android-dropbear
Another thank you to the various other repositories out there whose various approches helped lead to this completed project.