tpm2-ssh-agent

SSH agent using TPM 2.0

Example setup

$ tpm2_createprimary -C o -c primary.ctx -g sha256 -G ecc
name-alg:
  value: sha256
  raw: 0xb
...

$ tpm2_create -C primary.ctx -g sha256 -G rsa -u public -r private
name-alg:
  value: sha256
  raw: 0xb
...

$ cat public private > rsa-key
$ tpm2-ssh-agent --socket /tmp/test.socket --key rsa-key -f

And to check that it works

$ SSH_AUTH_SOCK=/tmp/test.socket ssh-add -L
ssh-rsa AAAA....

Example ssh hostkey setup using OpenRC scripts

• Create key and store it

# tpm2_createprimary -C o -c primary.ctx -g sha256 -G ecc
# tpm2_create -C primary.ctx -g sha256 -G rsa -u public -r private
# cat public private > /etc/ssh/ssh_hostagent_rsa_key.tpm

• Configure tpm2-ssh-agent Change /etc/conf.d/tpm2-ssh-agent to it contains the key It is done by setting the path in tpm2_ssh_agent_keyfiles

# Configuration for /etc/init.d/tpm2-ssh-agent

# Options to pass to tpm2-ssh-agent
#tpm2_ssh_agent_opts=""

# Path for socket
tpm2_ssh_agent_socket="/run/tpm2_ssh_agent.socket"

# Space seperated list of key files
tpm2_ssh_agent_keyfiles="/etc/ssh/ssh_hostagent_rsa_key.tpm"

# Space seperated list of key handles
#tpm2_ssh_agent_keyhandles=""

• Enable and start the service

# rc-update add tpm2-ssh-agent
# service tpm2-ssh-agent start

• Get the public in ssh format

# SSH_AUTH_SOCK=/run/tpm2_ssh_agent.socket ssh-add -L

Store the output in /etc/ssh/ssh_hostagent_rsa_key

• Configure sshd Add the following lines after the "HostKey ..." lines

HostKey /etc/ssh/ssh_hostagent_rsa_key
HostKeyAgent /run/tpm2_ssh_agent.socket

Disable the other HostKey lines by commenting them with '#'

• Restart sshd

# service sshd restart

• Verify that sshd uses the key Run ssh-keyscan to get the public key

# ssh-keyscan -t rsa localhost
# localhost:22 SSH-2.0-OpenSSH_8.1
localhost ssh-rsa AAAA...

Check that the key from ssh-keyscan is the same in /etc/ssh/ssh_hostagent_rsa_key

If nothing failed your ssh daemon should now use your TPM key!