Added ssh-tpm-hostkey docs and fixups

Signed-off-by: Morten Linderud <morten@linderud.pw>

README.md

@@ -177,6 +177,41 @@ $ ssh-add -L
 ecdsa-sha2-nistp256 AAAAE2VjZHNhLXNoYTItbmlzdHAyNTYAAAAIbmlzdHAyNTYAAABBBJCxqisGa9IUNh4Ik3kwihrDouxP7S5Oun2hnzTvFwktszaibJruKLJMxHqVYnNwKD9DegCNwUN1qXCI/UOwaSY= test
 ```
 
+### ssh-tpm-hostkey
+
+`ssh-tpm-agent` also supports storing host keys inside the TPM.
+
+```
+$ sudo ssh-tpm-keygen -A
+2023/09/03 17:03:08 INFO Generating new ECDSA host key
+2023/09/03 17:03:08 INFO Wrote /etc/ssh/ssh_tpm_host_ecdsa_key.tpm
+2023/09/03 17:03:08 INFO Generating new RSA host key
+2023/09/03 17:03:15 INFO Wrote /etc/ssh/ssh_tpm_host_rsa_key.tpm
+
+$ sudo ssh-tpm-hostkeys --install-system-units
+Installed /usr/lib/systemd/system/ssh-tpm-agent.service
+Installed /usr/lib/systemd/system/ssh-tpm-agent.socket
+Installed /usr/lib/systemd/system/ssh-tpm-genkeys.service
+Enable with: systemctl enable --now ssh-tpm-agent.socket
+
+$ sudo ssh-tpm-hostkeys --install-sshd-config
+Installed /etc/ssh/sshd_config.d/10-ssh-tpm-agent.conf
+Restart sshd: systemd restart sshd
+
+$ systemctl enable --now ssh-tpm-agent.socket
+$ systemd restart sshd
+
+$ sudo ssh-tpm-hostkeys
+ecdsa-sha2-nistp256 AAAAE2VjZHNhLXNoYTItbmlzdHAyNTYAAAAIbmlzdHAyNTYAAABBBCLDH2xMDIGb26Q3Fa/kZDuPvzLzfAH6CkNs0wlaY2AaiZT2qJkWI05lMDm+mf+wmDhhgQlkJAHmyqgzYNwqWY0= root@framework
+ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQDAoMPsv5tEpTDFw34ltkF45dTHAPl4aLu6HigBkNnIzsuWqJxhjN6JK3vaV3eXBzy8/UJxo/R0Ml9/DRzFK8cccdIRT1KQtg8xIikRReZ0usdeqTC+wLpW/KQqgBLZ1PphRINxABWReqlnbtPVBfj6wKlCVNLEuTfzi1oAMj3KXOBDcTTB2UBLcwvTFg6YnbTjrpxY83Y+3QIZNPwYqd7r6k+e/ncUl4zgCvvxhoojGxEM3pjQIaZ0Him0yT6OGmCGFa7XIRKxwBSv9HtyHf5psgI+X5A2NV2JW2xeLhV2K1+UXmKW4aXjBWKSO08lPSWZ6/5jQTGN1Jg3fLQKSe7f root@framework
+
+$ ssh-keyscan -t ecdsa localhost
+# localhost:22 SSH-2.0-OpenSSH_9.4
+localhost ecdsa-sha2-nistp256 AAAAE2VjZHNhLXNoYTItbmlzdHAyNTYAAAAIbmlzdHAyNTYAAABBBCLDH2xMDIGb26Q3Fa/kZDuPvzLzfAH6CkNs0wlaY2AaiZT2qJkWI05lMDm+mf+wmDhhgQlkJAHmyqgzYNwqWY0=
+```
+
+Note: sshd seems to be a bit flakey when it decides to sign with `SHA256` or `SHA512`, so your mileage might vary. Only `SHA256` is supported by `ssh-tpm-agent`.
+
 # ssh-config
 
 It is possible to use the public keys created by `ssh-tpm-keygen` inside ssh

cmd/ssh-tpm-hostkeys/main.go

@@ -20,6 +20,7 @@ const usage = `Usage:
 Options:
     --install-system-units    Installs systemd system units and sshd configs for using
                               ssh-tpm-agent as a hostkey agent.
+    --install-sshd-config     Installs sshd configuration for the ssh-tpm-agent socket.
 
 Display host keys.`
 
@@ -30,17 +31,22 @@ func main() {
 
 	var (
 		installSystemUnits bool
+		installSshdConfig  bool
 	)
 
 	flag.BoolVar(&installSystemUnits, "install-system-units", false, "install systemd system units")
+	flag.BoolVar(&installSshdConfig, "install-sshd-config", false, "install sshd config")
 	flag.Parse()
 
 	if installSystemUnits {
 		if err := utils.InstallSystemUnits(); err != nil {
 			log.Fatal(err)
 		}
+		os.Exit(0)
+	}
+	if installSshdConfig {
 		if err := utils.InstallSshdConf(); err != nil {
-			log.Printf("didn't install sshd config: %v", err)
+			log.Fatal(err)
 		}
 		os.Exit(0)
 	}

contrib/contrib.go

@@ -13,9 +13,9 @@ var sshd embed.FS
 
 func readPath(f embed.FS, s string) map[string][]byte {
 	ret := map[string][]byte{}
-	files, _ := services.ReadDir(s)
+	files, _ := f.ReadDir(s)
 	for _, file := range files {
-		b, _ := services.ReadFile(path.Join(s, file.Name()))
+		b, _ := f.ReadFile(path.Join(s, file.Name()))
 		ret[file.Name()] = b
 	}
 	return ret

contrib/contrib_test.go

@@ -17,3 +17,10 @@ func TestSystemServices(t *testing.T) {
 		t.Fatalf("invalid number of entries")
 	}
 }
+
+func TestSshdConfig(t *testing.T) {
+	m := GetSshdConfig()
+	if len(m) != 1 {
+		t.Fatalf("invalid number of entries")
+	}
+}

contrib/sshd/10-ssh-tpm-agent.conf

@@ -1,5 +1,6 @@
 # This enables TPM sealed host keys
 
 HostKeyAgent /var/tmp/ssh-tpm-agent.sock
-HostKey /etc/ssh/keys/ssh_host_ecdsa_key.pub
-HostKey /etc/ssh/keys/ssh_host_rsa_key.pub
+
+HostKey /etc/ssh/ssh_tpm_host_ecdsa_key.pub
+HostKey /etc/ssh/ssh_tpm_host_rsa_key.pub

utils/utils.go

@@ -48,7 +48,7 @@ func FileExists(s string) bool {
 // but here we are.
 func fmtSystemdInstallPath() string {
 	DESTDIR := ""
-	PREFIX := "/usr/local"
+	PREFIX := "/usr/"
 	if s, ok := os.LookupEnv("DESTDIR"); ok {
 		DESTDIR = s
 	}
@@ -163,7 +163,7 @@ func InstallSshdConf() error {
 		return nil
 	}
 
-	files := contrib.GetSystemServices()
+	files := contrib.GetSshdConfig()
 	for name := range files {
 		ff := path.Join(sshdConfInstallPath, name)
 		if FileExists(ff) {