examples: tls: Add a simple TLS example

Was useful for testing things...

examples/tls/tls.go

@@ -0,0 +1,203 @@
+// Modified from: golang/src/crypto/tls/generate_cert.go
+
+package main
+
+import (
+	"crypto/ecdsa"
+	"crypto/ed25519"
+	"crypto/elliptic"
+	"crypto/rand"
+	"crypto/rsa"
+	"crypto/x509"
+	"crypto/x509/pkix"
+	"encoding/pem"
+	"fmt"
+	"log"
+	"math/big"
+	"net"
+	"net/http"
+	"os"
+	"strings"
+	"time"
+)
+
+// NewTLS builds a new TLS struct with some defaults.
+func NewTLS() *TLS {
+	return &TLS{
+		ValidFor: 365 * 24 * time.Hour,
+		RsaBits:  2048,
+	}
+}
+
+// TLS handles all of the TLS building.
+type TLS struct {
+	Host       string        // Comma-separated hostnames and IPs to generate a certificate for
+	ValidFrom  string        // Creation date formatted as Jan 1 15:04:05 2011
+	ValidFor   time.Duration // Duration that certificate is valid for
+	IsCA       bool          // Whether this cert should be its own Certificate Authority
+	RsaBits    int           // Size of RSA key to generate. Ignored if EcdsaCurve is set
+	EcdsaCurve string        // ECDSA curve to use to generate a key. Valid values are P224, P256 (recommended), P384, P521
+	Ed25519Key bool          // Generate an Ed25519 key
+}
+
+// Generate writes out the two files. Usually keyPemFile is key.pem and
+// certPemFile is cert.pem which go into http.ListenAndServeTLS.
+func (obj *TLS) Generate(keyPemFile, certPemFile string) error {
+
+	if len(obj.Host) == 0 {
+		return fmt.Errorf("missing required Host parameter")
+	}
+
+	var priv any
+	var err error
+	switch obj.EcdsaCurve {
+	case "":
+		if obj.Ed25519Key {
+			_, priv, err = ed25519.GenerateKey(rand.Reader)
+		} else {
+			priv, err = rsa.GenerateKey(rand.Reader, obj.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:
+		return fmt.Errorf("unrecognized elliptic curve: %q", obj.EcdsaCurve)
+	}
+	if err != nil {
+		return fmt.Errorf("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(obj.ValidFrom) == 0 {
+		notBefore = time.Now()
+	} else {
+		notBefore, err = time.Parse("Jan 2 15:04:05 2006", obj.ValidFrom)
+		if err != nil {
+			return fmt.Errorf("failed to parse creation date: %v", err)
+		}
+	}
+
+	notAfter := notBefore.Add(obj.ValidFor)
+
+	serialNumberLimit := new(big.Int).Lsh(big.NewInt(1), 128)
+	serialNumber, err := rand.Int(rand.Reader, serialNumberLimit)
+	if err != nil {
+		return fmt.Errorf("failed to generate serial number: %v", err)
+	}
+
+	template := x509.Certificate{
+		SerialNumber: serialNumber,
+		Subject: pkix.Name{
+			Organization: []string{"Whatever Corp"}, // XXX: change me...
+		},
+		NotBefore: notBefore,
+		NotAfter:  notAfter,
+
+		KeyUsage:              keyUsage,
+		ExtKeyUsage:           []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth},
+		BasicConstraintsValid: true,
+	}
+
+	hosts := strings.Split(obj.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 obj.IsCA {
+		template.IsCA = true
+		template.KeyUsage |= x509.KeyUsageCertSign
+	}
+
+	derBytes, err := x509.CreateCertificate(rand.Reader, &template, &template, publicKey(priv), priv)
+	if err != nil {
+		return fmt.Errorf("failed to create certificate: %v", err)
+	}
+
+	certOut, err := os.Create(certPemFile)
+	if err != nil {
+		return fmt.Errorf("failed to open %s for writing: %v", certPemFile, err)
+	}
+	if err := pem.Encode(certOut, &pem.Block{Type: "CERTIFICATE", Bytes: derBytes}); err != nil {
+		return fmt.Errorf("failed to write data to %s: %v", certPemFile, err)
+	}
+	if err := certOut.Close(); err != nil {
+		return fmt.Errorf("error closing %s: %v", certPemFile, err)
+	}
+	log.Printf("wrote %s", certPemFile)
+
+	keyOut, err := os.OpenFile(keyPemFile, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0600)
+	if err != nil {
+		return fmt.Errorf("failed to open %s for writing: %v", keyPemFile, err)
+	}
+	privBytes, err := x509.MarshalPKCS8PrivateKey(priv)
+	if err != nil {
+		return fmt.Errorf("unable to marshal private key: %v", err)
+	}
+	if err := pem.Encode(keyOut, &pem.Block{Type: "PRIVATE KEY", Bytes: privBytes}); err != nil {
+		return fmt.Errorf("failed to write data to %s: %v", keyPemFile, err)
+	}
+	if err := keyOut.Close(); err != nil {
+		return fmt.Errorf("error closing %s: %v", keyPemFile, err)
+	}
+	log.Printf("wrote %s", keyPemFile)
+
+	return nil
+}
+
+// HelloServer is a simple handler.
+func HelloServer(w http.ResponseWriter, req *http.Request) {
+	fmt.Printf("req: %+v\n", req)
+	w.Header().Set("Content-Type", "text/plain")
+	w.Write([]byte("This is hello world!\n"))
+}
+
+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() {
+	// wget --no-check-certificate https://127.0.0.1:1443/hello -O -
+
+	tls := NewTLS()
+	tls.Host = "localhost" // TODO: choose something
+	keyPemFile := "/tmp/key.pem"
+	certPemFile := "/tmp/cert.pem"
+
+	if err := tls.Generate(keyPemFile, certPemFile); err != nil {
+		fmt.Printf("error: %v\n", err)
+		return
+	}
+
+	http.HandleFunc("/hello", HelloServer)
+	if err := http.ListenAndServeTLS(":1443", certPemFile, keyPemFile, nil); err != nil {
+		log.Fatal("ListenAndServe: ", err)
+	}
+}