6.8 KiB
SSH Agent
1. Configuration
SSH requires no configuration, but you may put common command line options in ~/.ssh/agent.conf to avoid repeating them in every invocation.
See (trezor|keepkey|ledger)-agent -h for details on supported options and the configuration file format.
If you'd like a Trezor-style PIN entry program, follow these instructions.
2. Usage
Use the (trezor|keepkey|ledger)-agent program to work with SSH. It has three main modes of operation:
1. Export public keys
To get your public key so you can add it to authorized_hosts or allow
ssh access to a service that supports it, run:
(trezor|keepkey|ledger)-agent identity@myhost
The identity (ex: identity@myhost) is used to derive the public key and is added as a comment to the exported key string.
2. Run a command with the agent's environment
Run
$ (trezor|keepkey|ledger)-agent identity@myhost -- COMMAND --WITH --ARGUMENTS
to start the agent in the background and execute the command with environment variables set up to use the SSH agent. The specified identity is used for all SSH connections. The agent will exit after the command completes.
Note the -- separator, which is used to separate trezor-agent's arguments from the SSH command arguments.
As a shortcut you can run
$ (trezor|keepkey|ledger)-agent identity@myhost -s
to start a shell with the proper environment.
2. Connect to a server directly via (trezor|keepkey|ledger)-agent
If you just want to connect to a server this is the simplest way to do it:
$ (trezor|keepkey|ledger)-agent user@remotehost -c
The identity user@remotehost is used as both the destination user and host as well as for key derivation, so you must generate a separate key for each host you connect to.
3. Common Use Cases
Start a single SSH session
Start multiple SSH sessions from a sub-shell
This feature allows using regular SSH-related commands within a subprocess running user's shell.
SSH_AUTH_SOCK environment variable is defined for the subprocess (pointing to the SSH agent, running as a parent process).
This way the user can use SSH-related commands (e.g. ssh, ssh-add, sshfs, git, hg), while authenticating via the hardware device.
Load different SSH identities from configuration file
Implement passwordless login
Run:
/tmp $ trezor-agent user@ssh.hostname.com -v > hostname.pub
2015-09-02 15:03:18,929 INFO getting "ssh://user@ssh.hostname.com" public key from Trezor...
2015-09-02 15:03:23,342 INFO disconnected from Trezor
/tmp $ cat hostname.pub
ecdsa-sha2-nistp256 AAAAE2VjZHNhLXNoYTItbmlzdHAyNTYAAAAIbmlzdHAyNTYAAABBBGSevcDwmT+QaZPUEWUUjTeZRBICChxMKuJ7dRpBSF8+qt+8S1GBK5Zj8Xicc8SHG/SE/EXKUL2UU3kcUzE7ADQ= ssh://user@ssh.hostname.com
Append hostname.pub contents to /home/user/.ssh/authorized_keys
configuration file at ssh.hostname.com, so the remote server
would allow you to login using the corresponding private key signature.
Access remote Git/Mercurial repositories
Export your public key and register it in your repository web interface (e.g. GitHub):
$ trezor-agent -v -e ed25519 git@github.com > ~/.ssh/github.pub
Add the following configuration to your ~/.ssh/config file:
Host github.com
IdentityFile ~/.ssh/github.pub
Use the following Bash alias for convenient Git operations:
$ alias ssh-shell='trezor-agent ~/.ssh/github.pub -v --shell'
Now, you can use regular Git commands under the "SSH-enabled" sub-shell:
$ ssh-shell
$ git push origin master
The same works for Mercurial (e.g. on BitBucket):
$ ssh-shell
$ hg push
Start the agent as a systemd unit
1. Create these files in ~/.config/systemd/user
Replace trezor with keepkey or ledger as required.
trezor-ssh-agent.service
[Unit]
Description=trezor-agent SSH agent
Requires=trezor-ssh-agent.socket
[Service]
Type=simple
Environment="DISPLAY=:0"
Environment="PATH=/bin:/usr/bin:/usr/local/bin:%h/.local/bin"
ExecStart=/usr/bin/trezor-agent --foreground --sock-path %t/trezor-agent/S.ssh IDENTITY
If you've installed trezor-agent locally you may have to change the path in ExecStart=.
Replace IDENTITY with the identity you used when exporting the public key.
If you have multiple Trezors connected, you can select which one to use via a TREZOR_PATH
environment variable. Use trezorctl list to find the correct path. Then add it
to the agent with the following line:
Environment="TREZOR_PATH=<your path here>"
Note that USB paths depend on the USB port which you use.
trezor-ssh-agent.socket
[Unit]
Description=trezor-agent SSH agent socket
[Socket]
ListenStream=%t/trezor-agent/S.ssh
FileDescriptorName=ssh
Service=trezor-ssh-agent.service
SocketMode=0600
DirectoryMode=0700
[Install]
WantedBy=sockets.target
2. Run
systemctl --user start trezor-ssh-agent.service trezor-ssh-agent.socket
systemctl --user enable trezor-ssh-agent.socket
3. Add this line to your .bashrc or equivalent file:
export SSH_AUTH_SOCK=$(systemctl show --user --property=Listen trezor-ssh-agent.socket | grep -o "/run.*")
4. SSH will now automatically use your device key in all terminals.
4. Troubleshooting
If SSH connection fails to work, please open an issue
with a verbose log attached (by running trezor-agent -vv) .
IdentitiesOnly SSH option
Note that your local SSH configuration may ignore trezor-agent, if it has IdentitiesOnly option set to yes.
IdentitiesOnly
Specifies that ssh(1) should only use the authentication identity files configured in
the ssh_config files, even if ssh-agent(1) or a PKCS11Provider offers more identities.
The argument to this keyword must be “yes” or “no”.
This option is intended for situations where ssh-agent offers many different identities.
The default is “no”.
If you are failing to connect, save your public key using:
$ trezor-agent -vv foobar@hostname.com > ~/.ssh/hostname.pub
And add the following lines to ~/.ssh/config (providing the public key explicitly to SSH):
Host hostname.com
User foobar
IdentityFile ~/.ssh/hostname.pub
Then, the following commands should successfully command to the remote host:
$ trezor-agent -v foobar@hostname.com -s
$ ssh foobar@hostname.com
or,
$ trezor-agent -v foobar@hostname.com -c