generate_cert.go

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