tls.go

/*-
 * Copyright 2015 Square Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package main

import (
	"crypto/tls"
	"crypto/x509"
	"encoding/pem"
	"io/ioutil"
	"sync/atomic"
	"unsafe"

	"golang.org/x/crypto/pkcs12"
)

// certificate wraps a TLS certificate in a reloadable way
type certificate struct {
	keystorePath, keystorePass string
	cached                     unsafe.Pointer
}

// Build reloadable certificate
func buildCertificate(keystorePath, keystorePass string) (*certificate, error) {
	cert := &certificate{keystorePath, keystorePass, nil}
	err := cert.reload()
	if err != nil {
		return nil, err
	}
	return cert, nil
}

// Retrieve actual certificate
func (c *certificate) getCertificate(clientHello *tls.ClientHelloInfo) (*tls.Certificate, error) {
	return (*tls.Certificate)(atomic.LoadPointer(&c.cached)), nil
}

// Reload certificate
func (c *certificate) reload() error {
	keystoreBytes, err := ioutil.ReadFile(c.keystorePath)
	if err != nil {
		return err
	}

	pemBlocks, err := pkcs12.ToPEM(keystoreBytes, c.keystorePass)
	if err != nil {
		return err
	}

	var pemBytes []byte
	for _, block := range pemBlocks {
		pemBytes = append(pemBytes, pem.EncodeToMemory(block)...)
	}

	certAndKey, err := tls.X509KeyPair(pemBytes, pemBytes)
	if err != nil {
		return err
	}

	certAndKey.Leaf, err = x509.ParseCertificate(certAndKey.Certificate[0])
	if err != nil {
		return err
	}

	atomic.StorePointer(&c.cached, unsafe.Pointer(&certAndKey))
	return nil
}

func caBundle(caBundlePath string) (*x509.CertPool, error) {
	if caBundlePath == "" {
		return x509.SystemCertPool()
	}

	caBundleBytes, err := ioutil.ReadFile(caBundlePath)
	if err != nil {
		return nil, err
	}

	bundle := x509.NewCertPool()
	bundle.AppendCertsFromPEM(caBundleBytes)
	return bundle, nil
}

// buildConfig reads command-line options and builds a tls.Config
func buildConfig(caBundlePath string) (*tls.Config, error) {
	ca, err := caBundle(caBundlePath)
	if err != nil {
		return nil, err
	}

	return &tls.Config{
		// Certificates
		RootCAs:   ca,
		ClientCAs: ca,

		PreferServerCipherSuites: true,

		ClientAuth: tls.RequireAndVerifyClientCert,
		MinVersion: tls.VersionTLS12,
		CipherSuites: []uint16{
			tls.TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256,
			tls.TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256,
			tls.TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384,
			tls.TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384,
		},
	}, nil
}