generate_cert.go

Documentation: crypto/tls

     1  // Copyright 2009 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  //go:build ignore
     6  // +build ignore
     7  
     8  // Generate a self-signed X.509 certificate for a TLS server. Outputs to
     9  // 'cert.pem' and 'key.pem' and will overwrite existing files.
    10  
    11  package main
    12  
    13  import (
    14  	"crypto/ecdsa"
    15  	"crypto/ed25519"
    16  	"crypto/elliptic"
    17  	"crypto/rand"
    18  	"crypto/rsa"
    19  	"crypto/x509"
    20  	"crypto/x509/pkix"
    21  	"encoding/pem"
    22  	"flag"
    23  	"log"
    24  	"math/big"
    25  	"net"
    26  	"os"
    27  	"strings"
    28  	"time"
    29  )
    30  
    31  var (
    32  	host       = flag.String("host", "", "Comma-separated hostnames and IPs to generate a certificate for")
    33  	validFrom  = flag.String("start-date", "", "Creation date formatted as Jan 1 15:04:05 2011")
    34  	validFor   = flag.Duration("duration", 365*24*time.Hour, "Duration that certificate is valid for")
    35  	isCA       = flag.Bool("ca", false, "whether this cert should be its own Certificate Authority")
    36  	rsaBits    = flag.Int("rsa-bits", 2048, "Size of RSA key to generate. Ignored if --ecdsa-curve is set")
    37  	ecdsaCurve = flag.String("ecdsa-curve", "", "ECDSA curve to use to generate a key. Valid values are P224, P256 (recommended), P384, P521")
    38  	ed25519Key = flag.Bool("ed25519", false, "Generate an Ed25519 key")
    39  )
    40  
    41  func publicKey(priv interface{}) interface{} {
    42  	switch k := priv.(type) {
    43  	case *rsa.PrivateKey:
    44  		return &k.PublicKey
    45  	case *ecdsa.PrivateKey:
    46  		return &k.PublicKey
    47  	case ed25519.PrivateKey:
    48  		return k.Public().(ed25519.PublicKey)
    49  	default:
    50  		return nil
    51  	}
    52  }
    53  
    54  func main() {
    55  	flag.Parse()
    56  
    57  	if len(*host) == 0 {
    58  		log.Fatalf("Missing required --host parameter")
    59  	}
    60  
    61  	var priv interface{}
    62  	var err error
    63  	switch *ecdsaCurve {
    64  	case "":
    65  		if *ed25519Key {
    66  			_, priv, err = ed25519.GenerateKey(rand.Reader)
    67  		} else {
    68  			priv, err = rsa.GenerateKey(rand.Reader, *rsaBits)
    69  		}
    70  	case "P224":
    71  		priv, err = ecdsa.GenerateKey(elliptic.P224(), rand.Reader)
    72  	case "P256":
    73  		priv, err = ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
    74  	case "P384":
    75  		priv, err = ecdsa.GenerateKey(elliptic.P384(), rand.Reader)
    76  	case "P521":
    77  		priv, err = ecdsa.GenerateKey(elliptic.P521(), rand.Reader)
    78  	default:
    79  		log.Fatalf("Unrecognized elliptic curve: %q", *ecdsaCurve)
    80  	}
    81  	if err != nil {
    82  		log.Fatalf("Failed to generate private key: %v", err)
    83  	}
    84  
    85  	// ECDSA, ED25519 and RSA subject keys should have the DigitalSignature
    86  	// KeyUsage bits set in the x509.Certificate template
    87  	keyUsage := x509.KeyUsageDigitalSignature
    88  	// Only RSA subject keys should have the KeyEncipherment KeyUsage bits set. In
    89  	// the context of TLS this KeyUsage is particular to RSA key exchange and
    90  	// authentication.
    91  	if _, isRSA := priv.(*rsa.PrivateKey); isRSA {
    92  		keyUsage |= x509.KeyUsageKeyEncipherment
    93  	}
    94  
    95  	var notBefore time.Time
    96  	if len(*validFrom) == 0 {
    97  		notBefore = time.Now()
    98  	} else {
    99  		notBefore, err = time.Parse("Jan 2 15:04:05 2006", *validFrom)
   100  		if err != nil {
   101  			log.Fatalf("Failed to parse creation date: %v", err)
   102  		}
   103  	}
   104  
   105  	notAfter := notBefore.Add(*validFor)
   106  
   107  	serialNumberLimit := new(big.Int).Lsh(big.NewInt(1), 128)
   108  	serialNumber, err := rand.Int(rand.Reader, serialNumberLimit)
   109  	if err != nil {
   110  		log.Fatalf("Failed to generate serial number: %v", err)
   111  	}
   112  
   113  	template := x509.Certificate{
   114  		SerialNumber: serialNumber,
   115  		Subject: pkix.Name{
   116  			Organization: []string{"Acme Co"},
   117  		},
   118  		NotBefore: notBefore,
   119  		NotAfter:  notAfter,
   120  
   121  		KeyUsage:              keyUsage,
   122  		ExtKeyUsage:           []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth},
   123  		BasicConstraintsValid: true,
   124  	}
   125  
   126  	hosts := strings.Split(*host, ",")
   127  	for _, h := range hosts {
   128  		if ip := net.ParseIP(h); ip != nil {
   129  			template.IPAddresses = append(template.IPAddresses, ip)
   130  		} else {
   131  			template.DNSNames = append(template.DNSNames, h)
   132  		}
   133  	}
   134  
   135  	if *isCA {
   136  		template.IsCA = true
   137  		template.KeyUsage |= x509.KeyUsageCertSign
   138  	}
   139  
   140  	derBytes, err := x509.CreateCertificate(rand.Reader, &template, &template, publicKey(priv), priv)
   141  	if err != nil {
   142  		log.Fatalf("Failed to create certificate: %v", err)
   143  	}
   144  
   145  	certOut, err := os.Create("cert.pem")
   146  	if err != nil {
   147  		log.Fatalf("Failed to open cert.pem for writing: %v", err)
   148  	}
   149  	if err := pem.Encode(certOut, &pem.Block{Type: "CERTIFICATE", Bytes: derBytes}); err != nil {
   150  		log.Fatalf("Failed to write data to cert.pem: %v", err)
   151  	}
   152  	if err := certOut.Close(); err != nil {
   153  		log.Fatalf("Error closing cert.pem: %v", err)
   154  	}
   155  	log.Print("wrote cert.pem\n")
   156  
   157  	keyOut, err := os.OpenFile("key.pem", os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0600)
   158  	if err != nil {
   159  		log.Fatalf("Failed to open key.pem for writing: %v", err)
   160  		return
   161  	}
   162  	privBytes, err := x509.MarshalPKCS8PrivateKey(priv)
   163  	if err != nil {
   164  		log.Fatalf("Unable to marshal private key: %v", err)
   165  	}
   166  	if err := pem.Encode(keyOut, &pem.Block{Type: "PRIVATE KEY", Bytes: privBytes}); err != nil {
   167  		log.Fatalf("Failed to write data to key.pem: %v", err)
   168  	}
   169  	if err := keyOut.Close(); err != nil {
   170  		log.Fatalf("Error closing key.pem: %v", err)
   171  	}
   172  	log.Print("wrote key.pem\n")
   173  }
   174
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