Recently I needed to have SSH connection with Android development board but since no SSH daemon is included in the official Android release I had some troubles finding the right way to do it.
The following guide was tested on OMAP3 development board with Android Eclair but should be working on any (rooted/unlocked) phone with Android.
Instructions how to run dropbear sshd on Android device:
First you fetch the latest Dropbear sources:
git clone git://android.git.kernel.org/platform/external/dropbear.git
Since the Android has different paths, no password support, etc. we must fix this in the original sources by applying the patch found here:
http://pastebin.com/f3dedc5e7
...the only problem is that it's for older version of Dropbear so we must try to apply it manually :(
After patch was applied build with:
./configure --host=arm-none-linux-gnueabi --disable-zlib
make CC=arm-none-linux-gnueabi-gcc
In case you're unable to apply the patch correctly or something went wrong with the build here is a archive with prebuilt binaries (dropbear, dropbearkey, dropbearconvert):
Install:
To install dropbear on the desired gadget copy the binaries to some custom dir, e.g. /dropbear.
Setup the Server (Android):
Generate a RSA server key using dropbearkey:
dropbearkey -t rsa -f dropbear_rsa_host_key
Then create a dir /data/dropbear and copy dropbear_rsa_host_key there.
Test dropbear:
/dropbear/dropbear -r dropbear_rsa_host_key -F -E -v -s
This should show you the debuglog (the (-F) option means non-daemon mode).
Now we need to generate a key-pair for the client to connect with (Dropbear is run with the option -s (no-password) because there is no password support in Android):
//generates a private key
dropbearkey -t rsa -f /dropbear/id_rsa
//extract the public-key:
dropbearkey -f /dropbear/id_rsa -y > /dropbear/id_rsa.pub
We need to create /data/dropbear/.ssh and cat the public-key to authorized_keys:
mkdir /data/dropbear/.ssh
cat /dropbear/id_rsa.pub > /data/dropbear/.ssh/authorized_keys
IMPORTATNT: Check the perms of /data/dropbear and make sure they are *only* readable/writable by root!
Setup the Client (Ubuntu):
As dropbear and openssh use different key formats we first need to convert id_rsa (private key) to openssh-format:
./dropbearconvert dropbear openssh /dropbear/id_rsa /dropbear/id_rsa_openssh
Now move id_rsa and id_rsa_openssh to your desktop (e.g. to your home dir).
Before establishing connection gadget's USB interface should be UP:
busybox ifconfig usb0 up 192.168.1.2
(yes, busybox must be installed on the Android device...)
Finally connect to the device:
ssh -i id_rsa_openssh <device-ip>
You can use -vv for both the client and the server to see debug info and fix whatever is wrong.
Setup the Client (Windows XP):
The only difference is that we use different SSH client. I used
PuTTY.
So...
- boot the board/phone
- connect PC with board with USB cable and wait for auto install
- set IP address (TCP/IP settings) in the automatically created USB Ethernet connection
- copy auth. keys generated with dropbear
- convert OpenSSH key to "PuTTY" key (ppk) using
PuTTYGen
- open PuTTY and set remote IP/Port to connect to
- use SSH key generated with PuttyGen: Connection -> SSH -> Auth -> select key
- connect!
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