gencert.go

package main

import (
	"crypto/rand"
	"crypto/rsa"
	"crypto/x509"
	"crypto/x509/pkix"
	"encoding/pem"
	"log"
	"math/big"
	"net"
	"os"
	"path/filepath"
	"strings"
	"time"
)

func pemBlockForKey(priv *rsa.PrivateKey) *pem.Block {
	return &pem.Block{
		Type:  "RSA PRIVATE KEY",
		Bytes: x509.MarshalPKCS1PrivateKey(priv),
	}
}

func genCert(hosts string) {
	priv, err := rsa.GenerateKey(rand.Reader, 4096)
	if err != nil {
		log.Fatalf("failed to generate private key: %s", err)
	}

	notBefore := time.Now()
	notAfter := notBefore.Add(365 * 24 * time.Hour)

	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{"Acme Co"},
		},
		NotBefore:             notBefore,
		NotAfter:              notAfter,
		KeyUsage:              x509.KeyUsageKeyEncipherment | x509.KeyUsageDigitalSignature,
		ExtKeyUsage:           []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth},
		BasicConstraintsValid: true,
	}

	for _, h := range strings.Split(hosts, ",") {
		if ip := net.ParseIP(h); ip != nil {
			template.IPAddresses = append(template.IPAddresses, ip)
		} else {
			template.DNSNames = append(template.DNSNames, h)
		}
	}

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

	crt, err := os.Create(filepath.Join(usrDir, ".pchat", i+".crt"))
	if err != nil {
		log.Fatalf("failed to open %s.crt for writing: %s", i, err)
	}
	if err := pem.Encode(crt, &pem.Block{Type: "CERTIFICATE", Bytes: derBytes}); err != nil {
		log.Fatalf("failed to write data to %s.crt: %s", i, err)
	}
	if err := crt.Close(); err != nil {
		log.Fatalf("error closing %s.crt: %s", i, err)
	}

	key, err := os.OpenFile(filepath.Join(usrDir, ".pchat", i+".key"), os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0600)
	if err != nil {
		log.Fatalf("failed to open %s.key for writing: %s", i, err)
	}
	if err := pem.Encode(key, pemBlockForKey(priv)); err != nil {
		log.Fatalf("failed to write data to %s.key: %s", i, err)
	}
	if err := key.Close(); err != nil {
		log.Fatalf("error closing %s.key: %s", i, err)
	}
}