This is a fork of Matt Johnston's dropbear ssh client/server with some new features like:

• support for -o BatchMode=yes, -o ConnectTimeout=<secs> and -o UserKnownHostsFile=<path> for the client.
• allow the user to prevent the server from creating pidfiles with -P none; also allow that misfeature to be configured away at compile time with --disable-pidfile.
• a new -A <path> option to let the server use some other file than the remote user's ~/.ssh/authorized_keys.
• use of a unix domain socket instead of a pair of pipes for the stdin/out of the spawned command in non-interactive mode.
• a better password-reading function which doesn't depend on getpass() (which is deprecated and not available on android)

some incompatible changes:

• dbclient will exit with an error instead of hanging when the server wasn't able to allocate a pty and start a shell (721554d).
• allow -t (force pty) to work even when the stdin of the client is not a tty (57f9cc9); this simplifies using dropbear as a backend for command-line emulators. Unlike in openssh, a single -t should suffice.
• when in non-interactive mode, wait for an eof on the pipe reading from the child (e48d1b0); ssh dropbear_server '(sleep 1; echo foo) &' will now print foo just as when connecting to an openssh server. This simplifies scripts with background processes, brings it in line with popen()-like constructs, and allows for passing the stdin/out fd to kernel modules (like nbd or usbib) or to other processes via SCM_RIGHTS.
• allow -i (inetd mode) of the server to be combined with -E.
• send an empty string instead of vt100 for TERM if it wasn't set in the environment.
• two -a options are needed on the server to allow remote TCP forwarding to listen on all interfaces; a single -a will only cause it to accept the bind address specified by the user, if not empty.

and some fixes for:

• cross-compiling for and using it on android
• cross-compiling for openwrt
• building in another (sub-)directory

Build for Android with the NDK with:

autoreconf -i
ndk(){
	arch=$1; api=$2; configure=$3; shift 3
	ndk=${ANDROID_NDK:?please set the path to the Android NDK}
	CC=$ndk/toolchains/llvm/prebuilt/linux-x86_64/bin/$arch-linux-android$api-clang \
	  "$configure" --host="$arch-linux-android$api"
}
ndk aarch64 21 ./configure
make -j
make strip
adb push dropbear* dbclient scp ...

A smallish SSH server and client https://matt.ucc.asn.au/dropbear/dropbear.html

INSTALL.md has compilation instructions.

MULTI.md has instructions on making a multi-purpose binary (ie a single binary which performs multiple tasks, to save disk space).

SMALL.md has some tips on creating small binaries.

A mirror of the Dropbear website and tarballs is available at https://dropbear.nl/mirror/.

Please contact me if you have any questions/bugs found/features/ideas/comments etc There is also a mailing list https://lists.ucc.asn.au/mailman/listinfo/dropbear

Matt Johnston matt@ucc.asn.au

You can use ~/.ssh/authorized_keys in the same way as with OpenSSH, just put the key entries in that file. They should be of the form:

ssh-rsa AAAAB3NzaC1yc2EAAAABIwAAAIEAwVa6M6cGVmUcLl2cFzkxEoJd06Ub4bVDsYrWvXhvUV+ZAM9uGuewZBDoAqNKJxoIn0Hyd0NkyU99UVv6NWV/5YSHtnf35LKds56j7cuzoQpFIdjNwdxAN0PCET/MG8qyskG/2IE2DPNIaJ3Wy+Ws4IZEgdJgPlTYUBWWtCWOGc= someone@hostname

You must make sure that ~/.ssh, and the key file, are only writable by the user. Beware of editors that split the key into multiple lines.

Dropbear supports some options for authorized_keys entries, see the manpage.

Dropbear can do public key auth as a client, but you will have to convert OpenSSH style keys to Dropbear format, or use dropbearkey to create them.

If you have an OpenSSH-style private key ~/.ssh/id_rsa, you need to do:

dropbearconvert openssh dropbear ~/.ssh/id_rsa  ~/.ssh/id_rsa.db
dbclient -i ~/.ssh/id_rsa.db <hostname>

Dropbear does not support encrypted hostkeys though can connect to ssh-agent.

If you want to get the public-key portion of a Dropbear private key, look at dropbearkey's -y option.

To run the server, you need to generate server keys, this is one-off:

./dropbearkey -t rsa -f dropbear_rsa_host_key
./dropbearkey -t dss -f dropbear_dss_host_key
./dropbearkey -t ecdsa -f dropbear_ecdsa_host_key
./dropbearkey -t ed25519 -f dropbear_ed25519_host_key

Or alternatively convert OpenSSH keys to Dropbear:

./dropbearconvert openssh dropbear /etc/ssh/ssh_host_dsa_key dropbear_dss_host_key

You can also get Dropbear to create keys when the first connection is made - this is preferable to generating keys when the system boots. Make sure /etc/dropbear/ exists and then pass -R to the dropbear server.

If the server is run as non-root, you most likely won't be able to allocate a pty, and you cannot login as any user other than that running the daemon (obviously). Shadow passwords will also be unusable as non-root.

The Dropbear distribution includes a standalone version of OpenSSH's scp program. You can compile it with make scp. You may want to change the path of the ssh binary, specified by _PATH_SSH_PROGRAM in options.h. By default the progress meter isn't compiled in to save space, you can enable it by adding SCPPROGRESS=1 to the make commandline.