cmd/upbox/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.

// This file is adapted from $GOROOT/src/crypto/tls/generate_cert.go

// Generate a self-signed X.509 certificate for a TLS server.

package main

import (
	"crypto/ecdsa"
	"crypto/elliptic"
	"crypto/rand"
	"crypto/rsa"
	"crypto/x509"
	"crypto/x509/pkix"
	"encoding/pem"
	"fmt"
	"math/big"
	"os"
	"path/filepath"
	"time"
)

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
	}
}

func generateCert(dir string) error {
	priv, err := ecdsa.GenerateKey(elliptic.P521(), rand.Reader)
	if err != nil {
		return fmt.Errorf("failed to generate key: %s", err)
	}

	notBefore := time.Now()
	notAfter := notBefore.Add(24 * time.Hour)

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

	template := x509.Certificate{
		SerialNumber: serialNumber,
		Subject: pkix.Name{
			Organization: []string{"The Upspin Project"},
		},
		NotBefore: notBefore,
		NotAfter:  notAfter,

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

		DNSNames: []string{"localhost"},
	}

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

	certOut, err := os.Create(filepath.Join(dir, "cert.pem"))
	if err != nil {
		return fmt.Errorf("failed to open cert.pem for writing: %s", err)
	}
	if err := pem.Encode(certOut, &pem.Block{Type: "CERTIFICATE", Bytes: derBytes}); err != nil {
		return fmt.Errorf("failed to encode cert.pem: %s", err)
	}
	if err := certOut.Close(); err != nil {
		return fmt.Errorf("failed to write cert.pem: %s", err)
	}

	keyOut, err := os.OpenFile(filepath.Join(dir, "key.pem"), os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0600)
	if err != nil {
		return fmt.Errorf("failed to open key.pem for writing: %s", err)
	}
	if err := pem.Encode(keyOut, pemBlockForKey(priv)); err != nil {
		return fmt.Errorf("failed to encode key.pem: %s", err)
	}
	if err := keyOut.Close(); err != nil {
		return fmt.Errorf("failed to write cert.pem: %s", err)
	}

	return nil
}