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crypto/tls: make TLS 1.3 opt-in
Updates #30055 Change-Id: If68615c8e9daa4226125dcc6a6866f29f3cfeef1 Reviewed-on: https://go-review.googlesource.com/c/160997 Run-TryBot: Filippo Valsorda <filippo@golang.org> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Russ Cox <rsc@golang.org>
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@ -388,15 +388,25 @@ for {
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<h3 id="tls_1_3">TLS 1.3</h3>
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<p>
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Go 1.12 adds support in the <code>crypto/tls</code> package for TLS 1.3 as
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specified in <a href="https://www.rfc-editor.org/info/rfc8446">RFC 8446</a>.
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Go 1.12 adds opt-in support for TLS 1.3 in the <code>crypto/tls</code> package as
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specified by <a href="https://www.rfc-editor.org/info/rfc8446">RFC 8446</a>. It can
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be enabled by adding the value <code>tls13=1</code> to the <code>GODEBUG</code>
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environment variable. It will be enabled by default in Go 1.13.
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</p>
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Programs that did not set an explicit <code>MaxVersion</code> in
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<a href="/pkg/crypto/tls/#Config"><code>Config</code></a> will automatically negotiate
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TLS 1.3 if available. All TLS 1.2 features except <code>TLSUnique</code> in
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<p>
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To negotiate TLS 1.3, make sure you do not set an explicit <code>MaxVersion</code> in
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<a href="/pkg/crypto/tls/#Config"><code>Config</code></a> and run your program with
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the environment variable <code>GODEBUG=tls13=1</code> set.
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</p>
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<p>
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All TLS 1.2 features except <code>TLSUnique</code> in
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<a href="/pkg/crypto/tls/#ConnectionState"><code>ConnectionState</code></a>
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and renegotiation are available in TLS 1.3 and provide equivalent or
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better security and performance.
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better security and performance. Note that even though TLS 1.3 is backwards
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compatible with previous versions, certain legacy systems might not work
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correctly when attempting to negotiate it.
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</p>
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<p>
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@ -16,6 +16,7 @@ import (
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"io"
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"math/big"
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"net"
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"os"
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"strings"
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"sync"
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"time"
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@ -775,11 +776,53 @@ func (c *Config) supportedVersions(isClient bool) []uint16 {
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if isClient && v < VersionTLS10 {
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continue
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}
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// TLS 1.3 is opt-in in Go 1.12.
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if v == VersionTLS13 && !isTLS13Supported() {
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continue
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}
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versions = append(versions, v)
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}
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return versions
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}
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// tls13Support caches the result for isTLS13Supported.
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var tls13Support struct {
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sync.Once
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cached bool
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}
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// isTLS13Supported returns whether the program opted into TLS 1.3 via
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// GODEBUG=tls13=1. It's cached after the first execution.
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func isTLS13Supported() bool {
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tls13Support.Do(func() {
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tls13Support.cached = goDebugString("tls13") == "1"
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})
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return tls13Support.cached
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}
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// goDebugString returns the value of the named GODEBUG key.
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// GODEBUG is of the form "key=val,key2=val2".
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func goDebugString(key string) string {
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s := os.Getenv("GODEBUG")
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for i := 0; i < len(s)-len(key)-1; i++ {
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if i > 0 && s[i-1] != ',' {
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continue
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}
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afterKey := s[i+len(key):]
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if afterKey[0] != '=' || s[i:i+len(key)] != key {
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continue
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}
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val := afterKey[1:]
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for i, b := range val {
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if b == ',' {
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return val[:i]
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}
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}
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return val
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}
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return ""
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}
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func (c *Config) maxSupportedVersion(isClient bool) uint16 {
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supportedVersions := c.supportedVersions(isClient)
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if len(supportedVersions) == 0 {
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@ -18,10 +18,18 @@ import (
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"os"
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"reflect"
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"strings"
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"sync"
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"testing"
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"time"
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)
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func init() {
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// TLS 1.3 is opt-in for Go 1.12, but we want to run most tests with it enabled.
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// TestTLS13Switch below tests the disabled behavior. See Issue 30055.
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tls13Support.Do(func() {}) // defuse the sync.Once
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tls13Support.cached = true
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}
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var rsaCertPEM = `-----BEGIN CERTIFICATE-----
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MIIB0zCCAX2gAwIBAgIJAI/M7BYjwB+uMA0GCSqGSIb3DQEBBQUAMEUxCzAJBgNV
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BAYTAkFVMRMwEQYDVQQIDApTb21lLVN0YXRlMSEwHwYDVQQKDBhJbnRlcm5ldCBX
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@ -1076,18 +1084,47 @@ func TestEscapeRoute(t *testing.T) {
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VersionSSL30,
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}
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ss, cs, err := testHandshake(t, testConfig, testConfig)
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expectVersion(t, testConfig, testConfig, VersionTLS12)
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}
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func expectVersion(t *testing.T, clientConfig, serverConfig *Config, v uint16) {
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ss, cs, err := testHandshake(t, clientConfig, serverConfig)
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if err != nil {
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t.Fatalf("Handshake failed when support for TLS 1.3 was dropped: %v", err)
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t.Fatalf("Handshake failed: %v", err)
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}
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if ss.Version != VersionTLS12 {
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t.Errorf("Server negotiated version %x, expected %x", cs.Version, VersionTLS12)
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if ss.Version != v {
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t.Errorf("Server negotiated version %x, expected %x", cs.Version, v)
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}
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if cs.Version != VersionTLS12 {
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t.Errorf("Client negotiated version %x, expected %x", cs.Version, VersionTLS12)
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if cs.Version != v {
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t.Errorf("Client negotiated version %x, expected %x", cs.Version, v)
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}
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}
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// TestTLS13Switch checks the behavior of GODEBUG=tls13=[0|1]. See Issue 30055.
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func TestTLS13Switch(t *testing.T) {
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defer func(savedGODEBUG string) {
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os.Setenv("GODEBUG", savedGODEBUG)
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}(os.Getenv("GODEBUG"))
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os.Setenv("GODEBUG", "tls13=0")
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tls13Support.Once = sync.Once{} // reset the cache
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tls12Config := testConfig.Clone()
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tls12Config.MaxVersion = VersionTLS12
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expectVersion(t, testConfig, testConfig, VersionTLS12)
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expectVersion(t, tls12Config, testConfig, VersionTLS12)
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expectVersion(t, testConfig, tls12Config, VersionTLS12)
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expectVersion(t, tls12Config, tls12Config, VersionTLS12)
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os.Setenv("GODEBUG", "tls13=1")
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tls13Support.Once = sync.Once{} // reset the cache
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expectVersion(t, testConfig, testConfig, VersionTLS13)
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expectVersion(t, tls12Config, testConfig, VersionTLS12)
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expectVersion(t, testConfig, tls12Config, VersionTLS12)
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expectVersion(t, tls12Config, tls12Config, VersionTLS12)
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}
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// Issue 28744: Ensure that we don't modify memory
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// that Config doesn't own such as Certificates.
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func TestBuildNameToCertificate_doesntModifyCertificates(t *testing.T) {
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