tinysshd(8)

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 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 have features such: SSH1 protocol, compression, port forwarding, agent forwarding, X11 forwarding ...

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 (default)

    signing - ssh-ed25519

    key-exchange - curve25519-sha256

    symmetric - chacha20-poly1305@openssh.com

-S  disable state-of-the-art crypto

-p  enable post-quantum crypto (default)

    signing - TODO (not implemented yet)

    key-exchange - sntrup761x25519-sha512@openssh.com

    symmetric - chacha20-poly1305@openssh.com

-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)

-e command
    execute the given command instead of spawning the shell (disables exec/subsystem channel requests)

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
        SuccessExitStatus=111
        StandardInput=socket
        StandardError=journal
        [Install]
        WantedBy=multi-user.target

SEE ALSO
tinysshd-makekey(8), tinysshd-printkey(8)

https://tinyssh.org/