generate_cert.go

// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Generate a self-signed X.509 certificate for a TLS server. Outputs to
// 'cert.pem' and 'key.pem' and will overwrite existing files.

// Modified by the Gopcua Authors for use in creating an OPC-UA compliant client certificate

package main

import (
	"crypto/ecdsa"
	"crypto/rand"
	"crypto/rsa"
	"crypto/x509"
	"crypto/x509/pkix"
	"encoding/pem"
	"fmt"
	"log"
	"math/big"
	"net"
	"net/url"
	"os"
	"strings"
	"time"
)

func main() {
	var host = `localhost`
	var rsaBits = 1024
	var certFile = "cert.pem"
	var keyFile = "key.pem"

	priv, err := rsa.GenerateKey(rand.Reader, rsaBits)
	if err != nil {
		fmt.Printf("failed to generate private key: %s", err)
		panic(err)
	}

	notBefore := time.Now()
	notAfter := notBefore.Add(365 * 24 * time.Hour) // 1 year

	serialNumberLimit := new(big.Int).Lsh(big.NewInt(1), 128)
	serialNumber, err := rand.Int(rand.Reader, serialNumberLimit)
	if err != nil {
		fmt.Printf("failed to generate serial number: %s", err)
		panic(err)
	}

	template := x509.Certificate{
		SerialNumber: serialNumber,
		Subject: pkix.Name{
			Organization: []string{"Gopcua Test Client"},
		},
		NotBefore: notBefore,
		NotAfter:  notAfter,

		KeyUsage:              x509.KeyUsageContentCommitment | x509.KeyUsageKeyEncipherment | x509.KeyUsageDigitalSignature | x509.KeyUsageDataEncipherment | x509.KeyUsageCertSign,
		ExtKeyUsage:           []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth, x509.ExtKeyUsageClientAuth},
		BasicConstraintsValid: true,
	}

	hosts := strings.Split(host, ",")
	for _, h := range hosts {
		if ip := net.ParseIP(h); ip != nil {
			template.IPAddresses = append(template.IPAddresses, ip)
		} else {
			template.DNSNames = append(template.DNSNames, h)
		}

		if uri, err := url.Parse(h); err == nil {
			template.URIs = append(template.URIs, uri)
		}
	}

	derBytes, err := x509.CreateCertificate(rand.Reader, &template, &template, publicKey(priv), priv)
	if err != nil {
		fmt.Printf("Failed to create certificate: %s", err)
		panic(err)
	}

	certOut, err := os.Create(certFile)
	if err != nil {
		fmt.Printf("failed to open %s for writing: %s", certFile, err)
		panic(err)
	}

	if err := pem.Encode(certOut, &pem.Block{Type: "CERTIFICATE", Bytes: derBytes}); err != nil {
		fmt.Printf("failed to write data to %s: %s", certFile, err)
		panic(err)
	}

	if err := certOut.Close(); err != nil {
		fmt.Printf("error closing %s: %s", certFile, err)
		panic(err)
	}

	fmt.Printf("wrote %s", certFile)

	keyOut, err := os.OpenFile(keyFile, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0600)
	if err != nil {
		log.Printf("failed to open %s for writing: %s", keyFile, err)
		panic(err)
	}

	if err := pem.Encode(keyOut, pemBlockForKey(priv)); err != nil {
		fmt.Printf("failed to write data to %s: %s", keyFile, err)
		panic(err)
	}

	if err := keyOut.Close(); err != nil {
		fmt.Printf("error closing %s: %s", keyFile, err)
		panic(err)
	}

	fmt.Printf("wrote %s", keyFile)
}

func publicKey(priv interface{}) interface{} {
	switch k := priv.(type) {
	case *rsa.PrivateKey:
		return &k.PublicKey
	case *ecdsa.PrivateKey:
		return &k.PublicKey
	default:
		return nil
	}
}

func pemBlockForKey(priv interface{}) *pem.Block {
	switch k := priv.(type) {
	case *rsa.PrivateKey:
		return &pem.Block{Type: "RSA PRIVATE KEY", Bytes: x509.MarshalPKCS1PrivateKey(k)}
	case *ecdsa.PrivateKey:
		b, err := x509.MarshalECPrivateKey(k)
		if err != nil {
			fmt.Fprintf(os.Stderr, "Unable to marshal ECDSA private key: %v", err)
			os.Exit(2)
		}
		return &pem.Block{Type: "EC PRIVATE KEY", Bytes: b}
	default:
		return nil
	}
}