Generate a self signed root account-key assertion for snapd

self-signed-root-account-key-assertion.go

// -*- Mode: Go; indent-tabs-mode: t -*-

/*
 * Copyright (C) 2021 Canonical Ltd
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 3 as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 */

package main

import (
	"fmt"
	"io/ioutil"
	"log"
	"os"
	"os/exec"
	"time"

	"github.com/snapcore/snapd/asserts"
	"github.com/snapcore/snapd/asserts/sysdb"
	"github.com/snapcore/snapd/osutil"
)

func main() {
	// create a temporary directory to create our key in
	dir, err := ioutil.TempDir("", "test-account-key")
	if err != nil {
		log.Fatalf("error creating temp dir: %v", err)
	}
	os.Setenv("SNAP_GNUPG_HOME", dir)

	// now create a key with empty passphrase
	manager := asserts.NewGPGKeypairManager()
	if err := manager.Generate("", "default"); err != nil {
		log.Fatalf("error generating new key: %v", err)
	}

	privKey, err := manager.GetByName("default")
	if err != nil {
		log.Fatalf("error getting default gpg key: %v", err)
	}

	db, err := asserts.OpenDatabase(&asserts.DatabaseConfig{
		KeypairManager: asserts.NewMemoryKeypairManager(),
		Backstore:      asserts.NewMemoryBackstore(),
		Trusted:        sysdb.Trusted(),
	})
	if err != nil {
		log.Fatalf("error opening database: %v", err)
	}

	// for signing itself, import the private key we just created
	if err := db.ImportKey(privKey); err != nil {
		log.Fatalf("error importing private signing key: %v", err)
	}

	headers := map[string]interface{}{
		"account-id":          "testrootrepair",
		"name":                "test-root-repair",
		"since":               time.Now().Format(time.RFC3339),
		"authority-id":        "testrootrepair",
		"public-key-sha3-384": privKey.PublicKey().ID(),
	}

	// the public key is the body of the account key assertion
	body, err := asserts.EncodePublicKey(privKey.PublicKey())
	if err != nil {
		log.Fatalf("error encoding public key of private key: %v", err)
	}
  
  // sign the assertion, using the ID of the public part of the private key
	a, err := db.Sign(asserts.AccountKeyType, headers, body, privKey.PublicKey().ID())
	if err != nil {
		log.Fatalf("error signing account-key: %v", err)
	}

	// output the account-key assertion itself
	fmt.Println(string(asserts.Encode(a)))

	// also export the private key in ASCII so we can save that somewhere
	out, err := exec.Command("gpg", "--homedir", dir, "--export-secret-key", "-a", "default").CombinedOutput()
	if err != nil {
		log.Fatalf("error exporting private ascii key: %v", osutil.OutputErr(out, err))
	}
	fmt.Println(string(out))
}