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certgen.go
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certgen.go
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// 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
// 'public.crt' and 'private.key' and will overwrite existing files.
package main
import (
"crypto/ecdsa"
"crypto/ed25519"
"crypto/elliptic"
"crypto/rand"
"crypto/x509"
"crypto/x509/pkix"
"encoding/pem"
"flag"
"fmt"
"log"
"math/big"
"net"
"net/mail"
"net/url"
"os"
"os/user"
"regexp"
"strings"
"time"
)
var version = "(dev)"
var (
host = flag.String("host", "", "Comma-separated hostnames and IPs to generate a certificate for")
ecdsaCurve = flag.String("ecdsa-curve", "P256", "ECDSA curve to use to generate a key. Valid values are P224, P256 (recommended), P384, P521")
ed25519Key = flag.Bool("ed25519", false, "Generate an Ed25519 key")
orgName = flag.String("org-name", "Certgen Development", "Organization name used when generating the certs")
commonName = flag.String("common-name", "", "Common name for client cert")
isNoCA = flag.Bool("no-ca", false, "whether this cert should not be its own Certificate Authority")
isClient = flag.Bool("client", false, "whether this cert is a client certificate")
validFrom = flag.String("start-date", "", "Creation date formatted as Jan 1 15:04:05 2011")
validFor = flag.Duration("duration", 365*24*time.Hour, "Duration that certificate is valid for")
)
func publicKey(priv interface{}) interface{} {
switch k := priv.(type) {
case *ecdsa.PrivateKey:
return &k.PublicKey
case ed25519.PrivateKey:
return k.Public().(ed25519.PublicKey)
default:
return nil
}
}
var userAndHostname string
func init() {
u, err := user.Current()
if err == nil {
userAndHostname = u.Username + "@"
}
if h, err := os.Hostname(); err == nil {
userAndHostname += h
}
if err == nil && u.Name != "" && u.Name != u.Username {
userAndHostname += " (" + u.Name + ")"
}
}
func main() {
flag.Parse()
if len(*host) == 0 {
log.Fatalf("Missing required --host parameter")
}
var priv interface{}
var err error
switch *ecdsaCurve {
case "":
if *ed25519Key {
_, priv, err = ed25519.GenerateKey(rand.Reader)
}
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:
log.Fatalf("Unrecognized elliptic curve: %q", *ecdsaCurve)
}
if err != nil {
log.Fatalf("Failed to generate private key: %v", err)
}
// ECDSA, ED25519 subject keys should have the DigitalSignature
// KeyUsage bits set in the x509.Certificate template
keyUsage := x509.KeyUsageKeyEncipherment | x509.KeyUsageDigitalSignature
var notBefore time.Time
if len(*validFrom) == 0 {
notBefore = time.Now()
} else {
notBefore, err = time.Parse("Jan 2 15:04:05 2006", *validFrom)
if err != nil {
log.Fatalf("Failed to parse creation date: %v", err)
}
}
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: %v", err)
}
template := x509.Certificate{
SerialNumber: serialNumber,
Subject: pkix.Name{
Organization: []string{*orgName},
OrganizationalUnit: []string{userAndHostname},
},
NotBefore: notBefore,
NotAfter: notAfter,
KeyUsage: keyUsage,
BasicConstraintsValid: true,
}
if *isClient {
if *commonName != "" {
template.Subject.CommonName = *commonName
}
}
hosts := strings.Split(*host, ",")
for _, h := range hosts {
h = strings.TrimSpace(h)
if h == "" {
continue
}
if ip := net.ParseIP(h); ip != nil {
template.IPAddresses = append(template.IPAddresses, ip)
} else if email, err := mail.ParseAddress(h); err == nil && email.Address == h {
template.EmailAddresses = append(template.EmailAddresses, h)
} else if uriName, err := url.Parse(h); err == nil && uriName.Scheme != "" && uriName.Host != "" {
template.URIs = append(template.URIs, uriName)
} else {
template.DNSNames = append(template.DNSNames, h)
}
}
if len(template.IPAddresses) > 0 || len(template.DNSNames) > 0 || len(template.URIs) > 0 {
template.ExtKeyUsage = append(template.ExtKeyUsage, x509.ExtKeyUsageServerAuth)
}
if len(template.EmailAddresses) > 0 {
template.ExtKeyUsage = append(template.ExtKeyUsage, x509.ExtKeyUsageEmailProtection)
}
if *isClient {
template.ExtKeyUsage = append(template.ExtKeyUsage, x509.ExtKeyUsageClientAuth)
} else if !*isNoCA {
template.IsCA = true
template.KeyUsage |= x509.KeyUsageCertSign
}
pkey := publicKey(priv)
if pkey == nil {
log.Fatalln("Failed to create certificate: publicKey is nil")
}
derBytes, err := x509.CreateCertificate(rand.Reader, &template, &template, pkey, priv)
if err != nil {
log.Fatalf("Failed to create certificate: %v", err)
}
certName := "public.crt"
if *isClient {
certName = "client.crt"
}
certOut, err := os.Create(certName)
if err != nil {
log.Fatalf("Failed to open %s for writing: %v", certName, err)
}
if err := pem.Encode(certOut, &pem.Block{Type: "CERTIFICATE", Bytes: derBytes}); err != nil {
log.Fatalf("Failed to write data to %s: %v", certName, err)
}
if err := certOut.Close(); err != nil {
log.Fatalf("Error closing %s: %v", certName, err)
}
certKey := "private.key"
if *isClient {
certKey = "client.key"
}
keyOut, err := os.OpenFile(certKey, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0o600)
if err != nil {
log.Fatalf("Failed to open %s for writing: %v", certKey, err)
}
privBytes, err := x509.MarshalPKCS8PrivateKey(priv)
if err != nil {
log.Fatalf("Unable to marshal %s: %v", certKey, err)
}
if err := pem.Encode(keyOut, &pem.Block{Type: "PRIVATE KEY", Bytes: privBytes}); err != nil {
log.Fatalf("Failed to write data to %s: %v", certKey, err)
}
if err := keyOut.Close(); err != nil {
log.Fatalf("Error closing %s: %v", certKey, err)
}
secondLvlWildcardRegexp := regexp.MustCompile(`(?i)^\*\.[0-9a-z_-]+$`)
fmt.Printf("Created a new certificate '%v', '%v' valid for the following names 📜\n", certName, certKey)
for _, h := range hosts {
h = strings.TrimSpace(h)
if h == "" {
continue
}
fmt.Printf(" - %q\n", h)
if secondLvlWildcardRegexp.MatchString(h) {
fmt.Printf(" Warning: many browsers don't support second-level wildcards like %q ⚠️\n", h)
}
}
for _, h := range hosts {
h = strings.TrimSpace(h)
if h == "" {
continue
}
if strings.HasPrefix(h, "*.") {
fmt.Printf("\nReminder: X.509 wildcards only go one level deep, so this won't match a.b.%s ℹ️\n", h[2:])
break
}
}
}