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// Package tlsconfig provides primitives to retrieve secure-enough TLS configurations for both clients and servers.
//
// As a reminder from https://golang.org/pkg/crypto/tls/#Config:
// A Config structure is used to configure a TLS client or server. After one has been passed to a TLS function it must not be modified.
// A Config may be reused; the tls package will also not modify it.
package tlsconfig
import (
"crypto/tls"
"crypto/x509"
"encoding/pem"
"fmt"
"io/ioutil"
"os"
"github.com/pkg/errors"
)
// Options represents the information needed to create client and server TLS configurations.
type Options struct {
CAFile string
// If either CertFile or KeyFile is empty, Client() will not load them
// preventing the client from authenticating to the server.
// However, Server() requires them and will error out if they are empty.
CertFile string
KeyFile string
// client-only option
InsecureSkipVerify bool
// server-only option
ClientAuth tls.ClientAuthType
// If ExclusiveRootPools is set, then if a CA file is provided, the root pool used for TLS
// creds will include exclusively the roots in that CA file. If no CA file is provided,
// the system pool will be used.
ExclusiveRootPools bool
MinVersion uint16
// If Passphrase is set, it will be used to decrypt a TLS private key
// if the key is encrypted
Passphrase string
}
// Extra (server-side) accepted CBC cipher suites - will phase out in the future
var acceptedCBCCiphers = []uint16{
tls.TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA,
tls.TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA,
tls.TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA,
tls.TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA,
}
// DefaultServerAcceptedCiphers should be uses by code which already has a crypto/tls
// options struct but wants to use a commonly accepted set of TLS cipher suites, with
// known weak algorithms removed.
var DefaultServerAcceptedCiphers = append(clientCipherSuites, acceptedCBCCiphers...)
// ServerDefault returns a secure-enough TLS configuration for the server TLS configuration.
func ServerDefault(ops ...func(*tls.Config)) *tls.Config {
tlsConfig := &tls.Config{
// Avoid fallback by default to SSL protocols < TLS1.2
MinVersion: tls.VersionTLS12,
PreferServerCipherSuites: true,
CipherSuites: DefaultServerAcceptedCiphers,
}
for _, op := range ops {
op(tlsConfig)
}
return tlsConfig
}
// ClientDefault returns a secure-enough TLS configuration for the client TLS configuration.
func ClientDefault(ops ...func(*tls.Config)) *tls.Config {
tlsConfig := &tls.Config{
// Prefer TLS1.2 as the client minimum
MinVersion: tls.VersionTLS12,
CipherSuites: clientCipherSuites,
}
for _, op := range ops {
op(tlsConfig)
}
return tlsConfig
}
// certPool returns an X.509 certificate pool from `caFile`, the certificate file.
func certPool(caFile string, exclusivePool bool) (*x509.CertPool, error) {
// If we should verify the server, we need to load a trusted ca
var (
certPool *x509.CertPool
err error
)
if exclusivePool {
certPool = x509.NewCertPool()
} else {
certPool, err = SystemCertPool()
if err != nil {
return nil, fmt.Errorf("failed to read system certificates: %v", err)
}
}
pemData, err := ioutil.ReadFile(caFile)
if err != nil {
return nil, fmt.Errorf("could not read CA certificate %q: %v", caFile, err)
}
if !certPool.AppendCertsFromPEM(pemData) {
return nil, fmt.Errorf("failed to append certificates from PEM file: %q", caFile)
}
return certPool, nil
}
// isValidMinVersion checks that the input value is a valid tls minimum version
func isValidMinVersion(version uint16) bool {
_, ok := allTLSVersions[version]
return ok
}
// adjustMinVersion sets the MinVersion on `config`, the input configuration.
// It assumes the current MinVersion on the `config` is the lowest allowed.
func adjustMinVersion(options Options, config *tls.Config) error {
if options.MinVersion > 0 {
if !isValidMinVersion(options.MinVersion) {
return fmt.Errorf("Invalid minimum TLS version: %x", options.MinVersion)
}
if options.MinVersion < config.MinVersion {
return fmt.Errorf("Requested minimum TLS version is too low. Should be at-least: %x", config.MinVersion)
}
config.MinVersion = options.MinVersion
}
return nil
}
// IsErrEncryptedKey returns true if the 'err' is an error of incorrect
// password when trying to decrypt a TLS private key
func IsErrEncryptedKey(err error) bool {
return errors.Cause(err) == x509.IncorrectPasswordError
}
// getPrivateKey returns the private key in 'keyBytes', in PEM-encoded format.
// If the private key is encrypted, 'passphrase' is used to decrypted the
// private key.
func getPrivateKey(keyBytes []byte, passphrase string) ([]byte, error) {
// this section makes some small changes to code from notary/tuf/utils/x509.go
pemBlock, _ := pem.Decode(keyBytes)
if pemBlock == nil {
return nil, fmt.Errorf("no valid private key found")
}
var err error
if x509.IsEncryptedPEMBlock(pemBlock) { //nolint:staticcheck // Ignore SA1019 (IsEncryptedPEMBlock is deprecated)
keyBytes, err = x509.DecryptPEMBlock(pemBlock, []byte(passphrase)) //nolint:staticcheck // Ignore SA1019 (DecryptPEMBlock is deprecated)
if err != nil {
return nil, errors.Wrap(err, "private key is encrypted, but could not decrypt it")
}
keyBytes = pem.EncodeToMemory(&pem.Block{Type: pemBlock.Type, Bytes: keyBytes})
}
return keyBytes, nil
}
// getCert returns a Certificate from the CertFile and KeyFile in 'options',
// if the key is encrypted, the Passphrase in 'options' will be used to
// decrypt it.
func getCert(options Options) ([]tls.Certificate, error) {
if options.CertFile == "" && options.KeyFile == "" {
return nil, nil
}
errMessage := "Could not load X509 key pair"
cert, err := ioutil.ReadFile(options.CertFile)
if err != nil {
return nil, errors.Wrap(err, errMessage)
}
prKeyBytes, err := ioutil.ReadFile(options.KeyFile)
if err != nil {
return nil, errors.Wrap(err, errMessage)
}
prKeyBytes, err = getPrivateKey(prKeyBytes, options.Passphrase)
if err != nil {
return nil, errors.Wrap(err, errMessage)
}
tlsCert, err := tls.X509KeyPair(cert, prKeyBytes)
if err != nil {
return nil, errors.Wrap(err, errMessage)
}
return []tls.Certificate{tlsCert}, nil
}
// Client returns a TLS configuration meant to be used by a client.
func Client(options Options) (*tls.Config, error) {
tlsConfig := ClientDefault()
tlsConfig.InsecureSkipVerify = options.InsecureSkipVerify
if !options.InsecureSkipVerify && options.CAFile != "" {
CAs, err := certPool(options.CAFile, options.ExclusiveRootPools)
if err != nil {
return nil, err
}
tlsConfig.RootCAs = CAs
}
tlsCerts, err := getCert(options)
if err != nil {
return nil, err
}
tlsConfig.Certificates = tlsCerts
if err := adjustMinVersion(options, tlsConfig); err != nil {
return nil, err
}
return tlsConfig, nil
}
// Server returns a TLS configuration meant to be used by a server.
func Server(options Options) (*tls.Config, error) {
tlsConfig := ServerDefault()
tlsConfig.ClientAuth = options.ClientAuth
tlsCert, err := tls.LoadX509KeyPair(options.CertFile, options.KeyFile)
if err != nil {
if os.IsNotExist(err) {
return nil, fmt.Errorf("Could not load X509 key pair (cert: %q, key: %q): %v", options.CertFile, options.KeyFile, err)
}
return nil, fmt.Errorf("Error reading X509 key pair (cert: %q, key: %q): %v. Make sure the key is not encrypted.", options.CertFile, options.KeyFile, err)
}
tlsConfig.Certificates = []tls.Certificate{tlsCert}
if options.ClientAuth >= tls.VerifyClientCertIfGiven && options.CAFile != "" {
CAs, err := certPool(options.CAFile, options.ExclusiveRootPools)
if err != nil {
return nil, err
}
tlsConfig.ClientCAs = CAs
}
if err := adjustMinVersion(options, tlsConfig); err != nil {
return nil, err
}
return tlsConfig, nil
}
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