certMaker.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.

// +build ignore

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

package main

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

var (
  // host       = flag.String("237919c4.ngrok.io", "98e168f1.ngrok.io", "Comma-separated hostnames and IPs to generate a certificate for")
  host       = flag.String("localhost", "0.0.0.0", "Comma-separated hostnames and IPs to generate a certificate for")
  validFrom  = flag.String("start-date", "Mon Jan 6 23:54:57 2017", "Mon Jan 6 15:04:05 2016")
  validFor   = flag.Duration("duration", 365*24*time.Hour, "Duration that certificate is valid for")
  isCA       = flag.Bool("ca", true, "whether this cert should be its own Certificate Authority")
  rsaBits    = flag.Int("rsa-bits", 2048, "Size of RSA key to generate. Ignored if --ecdsa-curve is set")
  ecdsaCurve = flag.String("ecdsa-curve", "", "ECDSA curve to use to generate a key. Valid values are P224, P256, P384, P521")
)

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 main() {
  flag.Parse()

  if len(*host) == 0 {
    log.Fatalf("Missing required --host parameter")
  }

  var priv interface{}
  var err error
  switch *ecdsaCurve {
  case "":
    priv, err = rsa.GenerateKey(rand.Reader, *rsaBits)
  case "P224":
    priv, err = ecdsa.GenerateKey(elliptic.P224(), rand.Reader)
  case "P256":
    priv, err = ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
  case "P384":
    priv, err = ecdsa.GenerateKey(elliptic.P384(), rand.Reader)
  case "P521":
    priv, err = ecdsa.GenerateKey(elliptic.P521(), rand.Reader)
  default:
    fmt.Fprintf(os.Stderr, "Unrecognized elliptic curve: %q", *ecdsaCurve)
    os.Exit(1)
  }
  if err != nil {
    log.Fatalf("failed to generate private key: %s", err)
  }

  var notBefore time.Time
  if len(*validFrom) == 0 {
    notBefore = time.Now()
  } else {
    notBefore, err = time.Parse("Mon Jan 2 15:04:05 2006", *validFrom)
    if err != nil {
      fmt.Fprintf(os.Stderr, "Failed to parse creation date: %s\n", err)
      os.Exit(1)
    }
  }

  notAfter := notBefore.Add(*validFor)

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

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

    KeyUsage:              x509.KeyUsageKeyEncipherment | x509.KeyUsageDigitalSignature,
    ExtKeyUsage:           []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth},
    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 *isCA {
    template.IsCA = true
    template.KeyUsage |= x509.KeyUsageCertSign
  }

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

  certOut, err := os.Create("cert.pem")
  if err != nil {
    log.Fatalf("failed to open cert.pem for writing: %s", err)
  }
  pem.Encode(certOut, &pem.Block{Type: "CERTIFICATE", Bytes: derBytes})
  certOut.Close()
  log.Print("written cert.pem\n")

  keyOut, err := os.OpenFile("key.pem", os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0600)
  if err != nil {
    log.Print("failed to open key.pem for writing:", err)
    return
  }
  pem.Encode(keyOut, pemBlockForKey(priv))
  keyOut.Close()
  log.Print("written key.pem\n")
}