// Copyright 2009 The Go Authors, 2015-2016 Jeremy Rand. 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
// 'cert.pem' and 'key.pem' and will overwrite existing files.

// This code has been modified from the stock Go code to generate 
// "dehydrated certificates", suitable for inclusion in a Namecoin name.

package main

import (
	"bytes"
	"crypto/ecdsa"
	"crypto/elliptic"
	"crypto/rand"
	"crypto/rsa"
	//"crypto/x509"
	"crypto/x509/pkix"
	"encoding/base64"
	"encoding/pem"
	"flag"
	"fmt"
	"log"
	"math/big"
	"os"
	"time"
	"github.com/namecoin/ncdns/certdehydrate"
	"github.com/namecoin/ncdns/x509"
)

var (
	host       = flag.String("host", "", "Hostname to generate a certificate for (only use one)")
	validFrom  = flag.String("start-date", "", "Creation date formatted as Jan 1 15:04:05 2011")
	validTo    = flag.String("end-date", "", "End date formatted as Jan 1 15:04:05 2011")
	ecdsaCurve = flag.String("ecdsa-curve", "", "ECDSA curve to use to generate a key. Valid values are P224, P256, P384, P521")
	falseHost  = flag.String("false-host", "", "(Optional) Generate a false cert for this host; used to test x.509 implementations for safety regarding handling of the CA flag and KeyUsage")
)

func publicKey(priv interface{}) interface{} {
	switch k := priv.(type) {
	case *rsa.PrivateKey:
		return &k.PublicKey
	case *ecdsa.PrivateKey:
		return &k.PublicKey
	default:
		return nil
	}
}

func pemBlockForKey(priv interface{}) *pem.Block {
	switch k := priv.(type) {
	case *rsa.PrivateKey:
		return &pem.Block{Type: "RSA PRIVATE KEY", Bytes: x509.MarshalPKCS1PrivateKey(k)}
	case *ecdsa.PrivateKey:
		b, err := x509.MarshalECPrivateKey(k)
		if err != nil {
			fmt.Fprintf(os.Stderr, "Unable to marshal ECDSA private key: %v", err)
			os.Exit(2)
		}
		return &pem.Block{Type: "EC PRIVATE KEY", Bytes: b}
	default:
		return nil
	}
}

func main() {
	flag.Parse()

	if len(*host) == 0 {
		log.Fatalf("Missing required --host parameter")
	}
	if len(*validFrom) == 0 {
		log.Fatalf("Missing required --start-date parameter")
	}
	if len(*validTo) == 0 {
		log.Fatalf("Missing required --end-date parameter")
	}
	if len(*ecdsaCurve) == 0 {
		log.Fatalf("Missing required --ecdsa-curve parameter")
	}

	var priv interface{}
	var err error
	switch *ecdsaCurve {
	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:
		fmt.Fprintf(os.Stderr, "Unrecognized elliptic curve: %q", *ecdsaCurve)
		os.Exit(1)
	}
	if err != nil {
		log.Fatalf("failed to generate private key: %s", err)
	}

	var notBefore time.Time
	notBefore, err = time.Parse("Jan 2 15:04:05 2006", *validFrom)
	if err != nil {
		fmt.Fprintf(os.Stderr, "Failed to parse creation date: %s\n", err)
		os.Exit(1)
	}
	
	var notAfter time.Time
	notAfter, err = time.Parse("Jan 2 15:04:05 2006", *validTo)
	if err != nil {
		fmt.Fprintf(os.Stderr, "Failed to parse expiry date: %s\n", err)
		os.Exit(1)
	}
	
	timestampPrecision := int64(5 * 60)
	
	notBeforeFloored := time.Unix( ( notBefore.Unix() / timestampPrecision ) * timestampPrecision, 0 )
	notAfterFloored := time.Unix( ( notAfter.Unix() / timestampPrecision ) * timestampPrecision, 0 )
	
	// Serial components
	pubkeyBytes, err := x509.MarshalPKIXPublicKey(publicKey(priv))
	if err != nil {
		log.Fatalf("failed to marshal public key: %s", err)
	}
	pubkeyB64 := base64.StdEncoding.EncodeToString(pubkeyBytes)
	notBeforeScaled := notBeforeFloored.Unix() / timestampPrecision
	notAfterScaled := notAfterFloored.Unix() / timestampPrecision
	
	// Calculate serial
	serialDehydrated := certdehydrate.DehydratedCertificate {
		PubkeyB64: pubkeyB64,
		NotBeforeScaled: notBeforeScaled,
		NotAfterScaled: notAfterScaled,
	}
	serialNumber := big.NewInt(1)
	serialNumberBytes, err := serialDehydrated.SerialNumber(*host)
	if err != nil {
		log.Fatalf("Error calculating serial number: %s", err)
	}
	serialNumber.SetBytes(serialNumberBytes)

	template := x509.Certificate{
		SerialNumber: serialNumber,
		Subject: pkix.Name{
			CommonName: *host,
			SerialNumber: "Namecoin TLS Certificate",
		},
		NotBefore: notBeforeFloored,
		NotAfter:  notAfterFloored,

		// x509.KeyUsageKeyEncipherment is used for RSA key exchange, but not DHE/ECDHE key exchange.  Since everyone should be using ECDHE (due to forward secrecy), we disallow x509.KeyUsageKeyEncipherment in our template.
		//KeyUsage:              x509.KeyUsageKeyEncipherment | x509.KeyUsageDigitalSignature,
		KeyUsage:              x509.KeyUsageDigitalSignature, 
		ExtKeyUsage:           []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth},
		BasicConstraintsValid: true,
	}

	template.DNSNames = append(template.DNSNames, *host)

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

	certOut, err := os.Create("cert.pem")
	if err != nil {
		log.Fatalf("failed to open cert.pem for writing: %s", err)
	}
	pem.Encode(certOut, &pem.Block{Type: "CERTIFICATE", Bytes: derBytes})
	certOut.Close()
	log.Print("written cert.pem\n")

	keyOut, err := os.OpenFile("key.pem", os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0600)
	if err != nil {
		log.Print("failed to open key.pem for writing:", err)
		return
	}
	pem.Encode(keyOut, pemBlockForKey(priv))
	keyOut.Close()
	log.Print("written key.pem\n")
	
	parsedResult, err := x509.ParseCertificate(derBytes)
	if err != nil {
		log.Fatal("failed to parse output cert: ", err)
	}
	
	dehydrated, err := certdehydrate.DehydrateCert(parsedResult)
	if err != nil {
		log.Fatal("failed to dehydrate result cert: ", err)
	}
	
	rehydrated, err := certdehydrate.RehydrateCert(dehydrated)
	if err != nil {
		log.Fatal("failed to rehydrate result cert: ", err)
	}
	
	rehydratedDerBytes, err := certdehydrate.FillRehydratedCertTemplate(*rehydrated, *host)
	if err != nil {
		log.Fatal("failed to fill rehydrated result cert: ", err)
	}
	
	if ! bytes.Equal(derBytes, rehydratedDerBytes) {
		log.Fatal("ERROR: The cert did not rehydrate to an identical form.  This is a bug; do not use the generated certificate.")
	}
	
	log.Print("Your Namecoin cert is: {\"d8\":", dehydrated, "}")

	log.Print("SUCCESS: The cert rehydrated to an identical form.  Place the generated files in your HTTPS server, and place the above JSON in the \"tls\" field for your Namecoin name.");

	if len(*falseHost) > 0 {
		var falsePriv interface{}
		
		switch *ecdsaCurve {
		case "P224":
			falsePriv, err = ecdsa.GenerateKey(elliptic.P224(), rand.Reader)
		case "P256":
			falsePriv, err = ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
		case "P384":
			falsePriv, err = ecdsa.GenerateKey(elliptic.P384(), rand.Reader)
		case "P521":
			falsePriv, err = ecdsa.GenerateKey(elliptic.P521(), rand.Reader)
		default:
			fmt.Fprintf(os.Stderr, "Unrecognized elliptic curve: %q", *ecdsaCurve)
			os.Exit(1)
		}
		if err != nil {
			log.Fatalf("failed to generate false private key: %s", err)
		}
		
		falseSerialNumber := big.NewInt(2)

		falseTemplate := x509.Certificate{
			SerialNumber: falseSerialNumber,
			Subject: pkix.Name{
				CommonName: *falseHost,
				SerialNumber: "Namecoin TLS Certificate",
			},
			NotBefore: notBefore,
			NotAfter:  notAfter,
	
			// x509.KeyUsageKeyEncipherment is used for RSA key exchange, but not DHE/ECDHE key exchange.  Since everyone should be using ECDHE (due to forward secrecy), we disallow x509.KeyUsageKeyEncipherment in our template.
			//KeyUsage:              x509.KeyUsageKeyEncipherment | x509.KeyUsageDigitalSignature,
			KeyUsage:              x509.KeyUsageDigitalSignature, 
			ExtKeyUsage:           []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth},
			BasicConstraintsValid: true,
		}
	
		falseTemplate.DNSNames = append(falseTemplate.DNSNames, *falseHost)
		
		falseDerBytes, err := x509.CreateCertificate(rand.Reader, &falseTemplate, &template, publicKey(falsePriv), priv)
		if err != nil {
			log.Fatalf("Failed to create false certificate: %s", err)
		}
	
		falseCertOut, err := os.Create("falseCert.pem")
		if err != nil {
			log.Fatalf("failed to open falseCert.pem for writing: %s", err)
		}
		pem.Encode(falseCertOut, &pem.Block{Type: "CERTIFICATE", Bytes: falseDerBytes})
		falseCertOut.Close()
		log.Print("written falseCert.pem\n")
		
		falseKeyOut, err := os.OpenFile("falseKey.pem", os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0600)
		if err != nil {
			log.Print("failed to open falseKey.pem for writing:", err)
			return
		}
		pem.Encode(falseKeyOut, pemBlockForKey(falsePriv))
		falseKeyOut.Close()
		log.Print("written falseKey.pem\n")
	}
}