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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.
//go: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/ed25519"
"crypto/elliptic"
"crypto/rand"
"crypto/rsa"
"crypto/x509"
"crypto/x509/pkix"
"encoding/pem"
"flag"
"log"
"math/big"
"net"
"os"
"strings"
"time"
)
var (
host = flag.String("host", "", "Comma-separated hostnames and IPs to generate a certificate for")
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")
isCA = flag.Bool("ca", false, "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 (recommended), P384, P521")
ed25519Key = flag.Bool("ed25519", false, "Generate an Ed25519 key")
)
func publicKey(priv any) any {
switch k := priv.(type) {
case *rsa.PrivateKey:
return &k.PublicKey
case *ecdsa.PrivateKey:
return &k.PublicKey
case ed25519.PrivateKey:
return k.Public().(ed25519.PublicKey)
default:
return nil
}
}
func main() {
flag.Parse()
if len(*host) == 0 {
log.Fatalf("Missing required --host parameter")
}
var priv any
var err error
switch *ecdsaCurve {
case "":
if *ed25519Key {
_, priv, err = ed25519.GenerateKey(rand.Reader)
} else {
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:
log.Fatalf("Unrecognized elliptic curve: %q", *ecdsaCurve)
}
if err != nil {
log.Fatalf("Failed to generate private key: %v", err)
}
// ECDSA, ED25519 and RSA subject keys should have the DigitalSignature
// KeyUsage bits set in the x509.Certificate template
keyUsage := x509.KeyUsageDigitalSignature
// Only RSA subject keys should have the KeyEncipherment KeyUsage bits set. In
// the context of TLS this KeyUsage is particular to RSA key exchange and
// authentication.
if _, isRSA := priv.(*rsa.PrivateKey); isRSA {
keyUsage |= x509.KeyUsageKeyEncipherment
}
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{"Acme Co"},
},
NotBefore: notBefore,
NotAfter: notAfter,
KeyUsage: keyUsage,
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: %v", err)
}
certOut, err := os.Create("cert.pem")
if err != nil {
log.Fatalf("Failed to open cert.pem for writing: %v", err)
}
if err := pem.Encode(certOut, &pem.Block{Type: "CERTIFICATE", Bytes: derBytes}); err != nil {
log.Fatalf("Failed to write data to cert.pem: %v", err)
}
if err := certOut.Close(); err != nil {
log.Fatalf("Error closing cert.pem: %v", err)
}
log.Print("wrote cert.pem\n")
keyOut, err := os.OpenFile("key.pem", os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0600)
if err != nil {
log.Fatalf("Failed to open key.pem for writing: %v", err)
}
privBytes, err := x509.MarshalPKCS8PrivateKey(priv)
if err != nil {
log.Fatalf("Unable to marshal private key: %v", err)
}
if err := pem.Encode(keyOut, &pem.Block{Type: "PRIVATE KEY", Bytes: privBytes}); err != nil {
log.Fatalf("Failed to write data to key.pem: %v", err)
}
if err := keyOut.Close(); err != nil {
log.Fatalf("Error closing key.pem: %v", err)
}
log.Print("wrote key.pem\n")
}
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