tls.go

// Copyright 2014 The Cockroach Authors.
//
// 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 security

// TODO(jqmp): The use of TLS here is just a proof of concept; its security
// properties haven't been analyzed or audited.

import (
	"crypto/tls"
	"crypto/x509"

	"github.com/pkg/errors"
)

// EmbeddedCertsDir is the certs directory inside embedded assets.
// Embedded*{Cert,Key} are the filenames for embedded certs.
const (
	EmbeddedCertsDir     = "test_certs"
	EmbeddedCACert       = "ca.crt"
	EmbeddedCAKey        = "ca.key"
	EmbeddedNodeCert     = "node.crt"
	EmbeddedNodeKey      = "node.key"
	EmbeddedRootCert     = "client.root.crt"
	EmbeddedRootKey      = "client.root.key"
	EmbeddedTestUserCert = "client.testuser.crt"
	EmbeddedTestUserKey  = "client.testuser.key"
)

// LoadServerTLSConfig creates a server TLSConfig by loading the CA and server certs.
// The following paths must be passed:
// - sslCA: path to the CA certificate
// - sslCert: path to the server certificate
// - sslCertKey: path to the server key
// If the path is prefixed with "embedded=", load the embedded certs.
func LoadServerTLSConfig(sslCA, sslCert, sslCertKey string) (*tls.Config, error) {
	certPEM, err := assetLoaderImpl.ReadFile(sslCert)
	if err != nil {
		return nil, err
	}
	keyPEM, err := assetLoaderImpl.ReadFile(sslCertKey)
	if err != nil {
		return nil, err
	}
	caPEM, err := assetLoaderImpl.ReadFile(sslCA)
	if err != nil {
		return nil, err
	}
	return newServerTLSConfig(certPEM, keyPEM, caPEM)
}

// newServerTLSConfig creates a server TLSConfig from the supplied byte strings containing
// - the certificate of this node (should be signed by the CA),
// - the private key of this node.
// - the certificate of the cluster CA,
func newServerTLSConfig(certPEM, keyPEM, caPEM []byte) (*tls.Config, error) {
	cfg, err := newBaseTLSConfig(certPEM, keyPEM, caPEM)
	if err != nil {
		return nil, err
	}
	cfg.ClientAuth = tls.VerifyClientCertIfGiven
	cfg.ClientCAs = cfg.RootCAs
	// Use the default cipher suite from golang (RC4 is going away in 1.5).
	// Prefer the server-specified suite.
	cfg.PreferServerCipherSuites = true
	// Should we disable session resumption? This may break forward secrecy.
	// cfg.SessionTicketsDisabled = true
	return cfg, nil
}

// LoadClientTLSConfig creates a client TLSConfig by loading the CA and client certs.
// The following paths must be passed:
// - sslCA: path to the CA certificate
// - sslCert: path to the client certificate
// - sslCertKey: path to the client key
// If the path is prefixed with "embedded=", load the embedded certs.
func LoadClientTLSConfig(sslCA, sslCert, sslCertKey string) (*tls.Config, error) {
	certPEM, err := assetLoaderImpl.ReadFile(sslCert)
	if err != nil {
		return nil, err
	}
	keyPEM, err := assetLoaderImpl.ReadFile(sslCertKey)
	if err != nil {
		return nil, err
	}
	caPEM, err := assetLoaderImpl.ReadFile(sslCA)
	if err != nil {
		return nil, err
	}

	return newClientTLSConfig(certPEM, keyPEM, caPEM)
}

// newClientTLSConfig creates a client TLSConfig from the supplied byte strings containing:
// - the certificate of this client (should be signed by the CA),
// - the private key of this client.
// - the certificate of the cluster CA,
func newClientTLSConfig(certPEM, keyPEM, caPEM []byte) (*tls.Config, error) {
	return newBaseTLSConfig(certPEM, keyPEM, caPEM)
}

// newBaseTLSConfig returns a tls.Config initialized with the
// parameters that are common to clients and servers.
func newBaseTLSConfig(certPEM, keyPEM, caPEM []byte) (*tls.Config, error) {
	cert, err := tls.X509KeyPair(certPEM, keyPEM)
	if err != nil {
		return nil, err
	}

	certPool := x509.NewCertPool()

	if !certPool.AppendCertsFromPEM(caPEM) {
		return nil, errors.Errorf("failed to parse PEM data to pool")
	}

	return &tls.Config{
		Certificates: []tls.Certificate{cert},
		RootCAs:      certPool,

		// This is Go's default list of cipher suites (as of go 1.8.3),
		// with the following differences:
		// - 3DES-based cipher suites have been removed. This cipher is
		//   vulnerable to the Sweet32 attack and is sometimes reported by
		//   security scanners. (This is arguably a false positive since
		//   it will never be selected: Any TLS1.2 implementation MUST
		//   include at least one cipher higher in the priority list, but
		//   there's also no reason to keep it around)
		// - AES is always prioritized over ChaCha20. Go makes this decision
		//   by default based on the presence or absence of hardware AES
		//   acceleration.
		//   TODO(bdarnell): do the same detection here. See
		//   https://github.com/golang/go/issues/21167
		//
		// Note that some TLS cipher suite guidance (such as Mozilla's[1])
		// recommend replacing the CBC_SHA suites below with CBC_SHA384 or
		// CBC_SHA256 variants. We do not do this because Go does not
		// currerntly implement the CBC_SHA384 suites, and its CBC_SHA256
		// implementation is vulnerable to the Lucky13 attack and is disabled
		// by default.[2]
		//
		// [1]: https://wiki.mozilla.org/Security/Server_Side_TLS#Modern_compatibility
		// [2]: https://github.com/golang/go/commit/48d8edb5b21db190f717e035b4d9ab61a077f9d7
		CipherSuites: []uint16{
			tls.TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256,
			tls.TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384,
			tls.TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256,
			tls.TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384,
			tls.TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305,
			tls.TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305,
			tls.TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA,
			tls.TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA,
			tls.TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA,
			tls.TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA,
			tls.TLS_RSA_WITH_AES_128_GCM_SHA256,
			tls.TLS_RSA_WITH_AES_256_GCM_SHA384,
			tls.TLS_RSA_WITH_AES_128_CBC_SHA,
			tls.TLS_RSA_WITH_AES_256_CBC_SHA,
		},

		MinVersion: tls.VersionTLS12,
	}, nil
}