tls.go

package main

import (
	"crypto/rand"
	"crypto/rsa"
	"crypto/tls"
	"crypto/x509"
	"crypto/x509/pkix"
	"encoding/pem"
	"log"
	"math/big"
	"net"
	"time"
)

func (s *Server) generateTLSConfig(hosts []string) (*tls.Config, error) {
	cert, err := generateCertificate(hosts)
	if err != nil {
		return nil, err
	}
	return &tls.Config{Certificates: []tls.Certificate{*cert}}, nil
}

// mostly from https://golang.org/src/crypto/tls/generate_cert.go
func generateCertificate(hosts []string) (*tls.Certificate, error) {
	rsaBits := 2048
	validFor := 365 * 24 * time.Hour

	priv, err := rsa.GenerateKey(rand.Reader, rsaBits)
	if err != nil {
		log.Printf("Failed to generate private key: %v", err)
		return nil, err
	}

	keyUsage := x509.KeyUsageDigitalSignature | x509.KeyUsageKeyEncipherment

	notBefore := time.Now()
	notAfter := notBefore.Add(validFor)

	serialNumberLimit := new(big.Int).Lsh(big.NewInt(1), 128)
	serialNumber, err := rand.Int(rand.Reader, serialNumberLimit)
	if err != nil {
		log.Printf("Failed to generate serial number: %v", err)
		return nil, 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,
	}

	for _, h := range 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.Printf("Failed to create certificate: %v", err)
		return nil, err
	}

	certPem := pem.EncodeToMemory(&pem.Block{Type: "CERTIFICATE", Bytes: derBytes})

	privBytes, err := x509.MarshalPKCS8PrivateKey(priv)
	if err != nil {
		log.Printf("Unable to marshal private key: %v", err)
		return nil, err
	}
	keyPem := pem.EncodeToMemory(&pem.Block{Type: "PRIVATE KEY", Bytes: privBytes})

	cert, err := tls.X509KeyPair(certPem, keyPem)
	if err != nil {
		return nil, err
	}

	return &cert, nil
}