NAME

tinysshd - Tiny SSH daemon

SYNOPSIS

tinysshd [ options ] keydir

DESCRIPTION

tinysshd is a minimalistic SSH server which implements only a subset of SSHv2 features.

tinysshd supports only secure cryptography (minimum 128-bit security, protected against cache-timing attacks)

tinysshd doesn't implement unnecessary features (such as SSH1 protocol, compression, ...)

tinysshd doesn't implement older crypto (such as RSA, DSA, HMAC-MD5, HMAC-SHA1, 3DES, RC4, ...)

tinysshd doesn't implement unsafe features (such as password or hostbased authentication)

tinysshd doesn't use dynamic memory allocation (no allocation failures, etc.)

OPTIONS

-q: no error messages
-Q: print error messages (default)
-v: print extra information
-s: enable state-of-the-art crypto - ssh-ed25519, curve25519-sha256, chacha20-poly1305@openssh.com (default)
-S: disable state-of-the-art crypto
-p: enable post-quantum crypto - TODO, sntrup4591761x25519-sha512@tinyssh.org, chacha20-poly1305@openssh.com (default)
-P: disable post-quantum crypto
-l: use syslog instead of standard error output (useful for running from inetd)
-L: don't use syslog, use standard error output (default)
-x name=command: add subsystem command (e.g.: sftp=/usr/libexec/openssh/sftp-server)
keydir: directory containing TinySSH keys, typically /etc/tinyssh/sshkeydir

AUTHORIZATION

tinysshd supports only public-key authorization via AuthorizedKeysFile ~/.ssh/authorized_keys. Each line of the file contains one key in format "keytype base64-encoded-key comment". tinyssh supports only "ssh-ed25519" keytype.

~/.ssh/authorized_keys example:

ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAILV5AGhGQ1QVXjBWhTKJP3vrqE3isL4ivisBailQ14gS comment

RUNNING

TCPSERVER: tcpserver -HRDl0 0.0.0.0 22 /usr/sbin/tinysshd -v /etc/tinyssh/sshkeydir &
BUSYBOX: busybox tcpsvd 0 22 tinysshd -v /etc/tinyssh/sshkeydir &
INETD

/etc/inetd.conf:

ssh stream tcp nowait root /usr/sbin/tinysshd tinysshd -l -v /etc/tinyssh/sshkeydir

SYSTEMD

tinysshd.socket:

[Unit]
Description=TinySSH server socket
ConditionPathExists=!/etc/tinyssh/disable_tinysshd
[Socket]
ListenStream=22
Accept=yes
[Install]
WantedBy=sockets.target

tinysshd@.service:

[Unit]
Description=Tiny SSH server
After=network.target auditd.service
[Service]
ExecStartPre=-/usr/sbin/tinysshd-makekey -q /etc/tinyssh/sshkeydir
EnvironmentFile=-/etc/default/tinysshd
ExecStart=/usr/sbin/tinysshd ${TINYSSHDOPTS} -- /etc/tinyssh/sshkeydir
KillMode=process
StandardInput=socket
StandardError=journal
[Install]
WantedBy=multi-user.target