First as a side-note for other readers: We're not talking about "an app" here (those have already been tried and didn't work on that architecture), but about a command-line binary. DropBear sometimes is part of Busybox, or it comes as separate binary.
Now for the installation part. Binaries you install yourself best go to
/system/xbin, which is in the
$PATH but usually "initially empty" (Android's own stuff is in
/system/sbin), so we run a very low risk of "collisions". So either
adb shell or terminal to your device and make sure you're root. I further assume you've already transferred the
busybox binary to your SD card.
mount -o remount,rw /system # make sure we can write to system
cp /sdcard/busybox /system/xbin # copy the binaries to /system/xbin
cp /sdcard/dropbear /system/xbin
cd /system/xbin # switch to our target directory
chmod 755 busybox dropbear # make sure we've set the correct permissions
busybox --install /system/xbin # advice busybox to create all its symlinks here
Installation part done (skip the
dropbear parts here if your
dropbear comes with
busybox – and vice versa, skip the
busybox part if not needed.
Now, we need to make
dropbear fly. I've never tried this myself, so I refer to an external script at Github for that. In short (and in case that link dies), again assuming the required files are already copied to your SD card:
# Creating a home-dir for DropBear
chmod 755 /data/dropbear
chmod 700 /data/dropbear/.ssh
# Copy over our files
mv /sdcard/authorized_keys /data/dropbear/.ssh/
chown root: /data/dropbear/.ssh/authorized_keys
chmod 600 /data/dropbear/.ssh/authorized_keys
# Generate a hostkey, so we can use DropBear
dropbearkey -t rsa -f /data/dropbear/dropbear_rsa_host_key
dropbearkey -t dss -f /data/dropbear/dropbear_dss_host_key
An additional part if you want DropBear to auto-start at boot:
cat << EOF >> /etc/init.local.rc
# start Dropbear (ssh server) service on boot
service sshd /system/xbin/dropbear -s
Note that this assumes your device supports
init.d scripts. First check for the availability of that file to make sure.
Finally, don't forget to make
/system read-only again. Either reboot at this point (so you also can check that DropBear starts as intended), or at least execute
mount -o remount,ro /system
for now, postponing the reboot. To start the service manually, it should be possible executing that block via some shell script (so you could e.g. have a tasker task for starting and another one for stopping the daemon, and even make shortcuts to those tasks on your homescreen for manual control). Again, I have not tested this part, so it's "pure theory".
Good luck with DropBear and BusyBox!