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// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package tls
import (
const (
VersionSSL30 = 0x0300
VersionTLS10 = 0x0301
VersionTLS11 = 0x0302
VersionTLS12 = 0x0303
const (
maxPlaintext = 16384 // maximum plaintext payload length
maxCiphertext = 16384 + 2048 // maximum ciphertext payload length
recordHeaderLen = 5 // record header length
maxHandshake = 65536 // maximum handshake we support (protocol max is 16 MB)
minVersion = VersionTLS10
maxVersion = VersionTLS12
// TLS record types.
type recordType uint8
const (
recordTypeChangeCipherSpec recordType = 20
recordTypeAlert recordType = 21
recordTypeHandshake recordType = 22
recordTypeApplicationData recordType = 23
// TLS handshake message types.
const (
typeHelloRequest uint8 = 0
typeClientHello uint8 = 1
typeServerHello uint8 = 2
typeNewSessionTicket uint8 = 4
typeCertificate uint8 = 11
typeServerKeyExchange uint8 = 12
typeCertificateRequest uint8 = 13
typeServerHelloDone uint8 = 14
typeCertificateVerify uint8 = 15
typeClientKeyExchange uint8 = 16
typeFinished uint8 = 20
typeCertificateStatus uint8 = 22
typeNextProtocol uint8 = 67 // Not IANA assigned
// TLS compression types.
const (
compressionNone uint8 = 0
// TLS extension numbers
const (
extensionServerName uint16 = 0
extensionStatusRequest uint16 = 5
extensionSupportedCurves uint16 = 10
extensionSupportedPoints uint16 = 11
extensionSignatureAlgorithms uint16 = 13
extensionALPN uint16 = 16
extensionSCT uint16 = 18 //
extensionSessionTicket uint16 = 35
extensionNextProtoNeg uint16 = 13172 // not IANA assigned
extensionRenegotiationInfo uint16 = 0xff01
// TLS signaling cipher suite values
const (
scsvRenegotiation uint16 = 0x00ff
// CurveID is the type of a TLS identifier for an elliptic curve. See
type CurveID uint16
const (
CurveP256 CurveID = 23
CurveP384 CurveID = 24
CurveP521 CurveID = 25
X25519 CurveID = 29
// TLS Elliptic Curve Point Formats
const (
pointFormatUncompressed uint8 = 0
// TLS CertificateStatusType (RFC 3546)
const (
statusTypeOCSP uint8 = 1
// Certificate types (for certificateRequestMsg)
const (
certTypeRSASign = 1 // A certificate containing an RSA key
certTypeDSSSign = 2 // A certificate containing a DSA key
certTypeRSAFixedDH = 3 // A certificate containing a static DH key
certTypeDSSFixedDH = 4 // A certificate containing a static DH key
// See RFC 4492 sections 3 and 5.5.
certTypeECDSASign = 64 // A certificate containing an ECDSA-capable public key, signed with ECDSA.
certTypeRSAFixedECDH = 65 // A certificate containing an ECDH-capable public key, signed with RSA.
certTypeECDSAFixedECDH = 66 // A certificate containing an ECDH-capable public key, signed with ECDSA.
// Rest of these are reserved by the TLS spec
// Hash functions for TLS 1.2 (See RFC 5246, section A.4.1)
const (
hashSHA1 uint8 = 2
hashSHA256 uint8 = 4
hashSHA384 uint8 = 5
// Signature algorithms for TLS 1.2 (See RFC 5246, section A.4.1)
const (
signatureRSA uint8 = 1
signatureECDSA uint8 = 3
// signatureAndHash mirrors the TLS 1.2, SignatureAndHashAlgorithm struct. See
// RFC 5246, section A.4.1.
type signatureAndHash struct {
hash, signature uint8
// defaultSupportedSignatureAlgorithms contains the signature and hash algorithms that
// the code advertises as supported in a TLS 1.2 ClientHello and in a TLS 1.2
// CertificateRequest.
var defaultSupportedSignatureAlgorithms = []signatureAndHash{
{hashSHA256, signatureRSA},
{hashSHA256, signatureECDSA},
{hashSHA384, signatureRSA},
{hashSHA384, signatureECDSA},
{hashSHA1, signatureRSA},
{hashSHA1, signatureECDSA},
// ConnectionState records basic TLS details about the connection.
type ConnectionState struct {
Version uint16 // TLS version used by the connection (e.g. VersionTLS12)
HandshakeComplete bool // TLS handshake is complete
DidResume bool // connection resumes a previous TLS connection
CipherSuite uint16 // cipher suite in use (TLS_RSA_WITH_RC4_128_SHA, ...)
NegotiatedProtocol string // negotiated next protocol (not guaranteed to be from Config.NextProtos)
NegotiatedProtocolIsMutual bool // negotiated protocol was advertised by server (client side only)
ServerName string // server name requested by client, if any (server side only)
PeerCertificates []*x509.Certificate // certificate chain presented by remote peer
VerifiedChains [][]*x509.Certificate // verified chains built from PeerCertificates
SignedCertificateTimestamps [][]byte // SCTs from the server, if any
OCSPResponse []byte // stapled OCSP response from server, if any
// TLSUnique contains the "tls-unique" channel binding value (see RFC
// 5929, section 3). For resumed sessions this value will be nil
// because resumption does not include enough context (see
// This will
// change in future versions of Go once the TLS master-secret fix has
// been standardized and implemented.
TLSUnique []byte
// ClientAuthType declares the policy the server will follow for
// TLS Client Authentication.
type ClientAuthType int
const (
NoClientCert ClientAuthType = iota
// ClientSessionState contains the state needed by clients to resume TLS
// sessions.
type ClientSessionState struct {
sessionTicket []uint8 // Encrypted ticket used for session resumption with server
vers uint16 // SSL/TLS version negotiated for the session
cipherSuite uint16 // Ciphersuite negotiated for the session
masterSecret []byte // MasterSecret generated by client on a full handshake
serverCertificates []*x509.Certificate // Certificate chain presented by the server
verifiedChains [][]*x509.Certificate // Certificate chains we built for verification
// ClientSessionCache is a cache of ClientSessionState objects that can be used
// by a client to resume a TLS session with a given server. ClientSessionCache
// implementations should expect to be called concurrently from different
// goroutines. Only ticket-based resumption is supported, not SessionID-based
// resumption.
type ClientSessionCache interface {
// Get searches for a ClientSessionState associated with the given key.
// On return, ok is true if one was found.
Get(sessionKey string) (session *ClientSessionState, ok bool)
// Put adds the ClientSessionState to the cache with the given key.
Put(sessionKey string, cs *ClientSessionState)
// SignatureScheme identifies a signature algorithm supported by TLS. See
type SignatureScheme uint16
const (
PKCS1WithSHA1 SignatureScheme = 0x0201
PKCS1WithSHA256 SignatureScheme = 0x0401
PKCS1WithSHA384 SignatureScheme = 0x0501
PKCS1WithSHA512 SignatureScheme = 0x0601
PSSWithSHA256 SignatureScheme = 0x0804
PSSWithSHA384 SignatureScheme = 0x0805
PSSWithSHA512 SignatureScheme = 0x0806
ECDSAWithP256AndSHA256 SignatureScheme = 0x0403
ECDSAWithP384AndSHA384 SignatureScheme = 0x0503
ECDSAWithP521AndSHA512 SignatureScheme = 0x0603
// ClientHelloInfo contains information from a ClientHello message in order to
// guide certificate selection in the GetCertificate callback.
type ClientHelloInfo struct {
// CipherSuites lists the CipherSuites supported by the client (e.g.
CipherSuites []uint16
// ServerName indicates the name of the server requested by the client
// in order to support virtual hosting. ServerName is only set if the
// client is using SNI (see
ServerName string
// SupportedCurves lists the elliptic curves supported by the client.
// SupportedCurves is set only if the Supported Elliptic Curves
// Extension is being used (see
SupportedCurves []CurveID
// SupportedPoints lists the point formats supported by the client.
// SupportedPoints is set only if the Supported Point Formats Extension
// is being used (see
SupportedPoints []uint8
// SignatureSchemes lists the signature and hash schemes that the client
// is willing to verify. SignatureSchemes is set only if the Signature
// Algorithms Extension is being used (see
SignatureSchemes []SignatureScheme
// SupportedProtos lists the application protocols supported by the client.
// SupportedProtos is set only if the Application-Layer Protocol
// Negotiation Extension is being used (see
// Servers can select a protocol by setting Config.NextProtos in a
// GetConfigForClient return value.
SupportedProtos []string
// SupportedVersions lists the TLS versions supported by the client.
// For TLS versions less than 1.3, this is extrapolated from the max
// version advertised by the client, so values other than the greatest
// might be rejected if used.
SupportedVersions []uint16
// Conn is the underlying net.Conn for the connection. Do not read
// from, or write to, this connection; that will cause the TLS
// connection to fail.
Conn net.Conn
// CertificateRequestInfo contains information from a server's
// CertificateRequest message, which is used to demand a certificate and proof
// of control from a client.
type CertificateRequestInfo struct {
// AcceptableCAs contains zero or more, DER-encoded, X.501
// Distinguished Names. These are the names of root or intermediate CAs
// that the server wishes the returned certificate to be signed by. An
// empty slice indicates that the server has no preference.
AcceptableCAs [][]byte
// SignatureSchemes lists the signature schemes that the server is
// willing to verify.
SignatureSchemes []SignatureScheme
// RenegotiationSupport enumerates the different levels of support for TLS
// renegotiation. TLS renegotiation is the act of performing subsequent
// handshakes on a connection after the first. This significantly complicates
// the state machine and has been the source of numerous, subtle security
// issues. Initiating a renegotiation is not supported, but support for
// accepting renegotiation requests may be enabled.
// Even when enabled, the server may not change its identity between handshakes
// (i.e. the leaf certificate must be the same). Additionally, concurrent
// handshake and application data flow is not permitted so renegotiation can
// only be used with protocols that synchronise with the renegotiation, such as
type RenegotiationSupport int
const (
// RenegotiateNever disables renegotiation.
RenegotiateNever RenegotiationSupport = iota
// RenegotiateOnceAsClient allows a remote server to request
// renegotiation once per connection.
// RenegotiateFreelyAsClient allows a remote server to repeatedly
// request renegotiation.
// 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.
type Config struct {
// Rand provides the source of entropy for nonces and RSA blinding.
// If Rand is nil, TLS uses the cryptographic random reader in package
// crypto/rand.
// The Reader must be safe for use by multiple goroutines.
Rand io.Reader
// Time returns the current time as the number of seconds since the epoch.
// If Time is nil, TLS uses time.Now.
Time func() time.Time
// Certificates contains one or more certificate chains to present to
// the other side of the connection. Server configurations must include
// at least one certificate or else set GetCertificate. Clients doing
// client-authentication may set either Certificates or
// GetClientCertificate.
Certificates []Certificate
// NameToCertificate maps from a certificate name to an element of
// Certificates. Note that a certificate name can be of the form
// '*' and so doesn't have to be a domain name as such.
// See Config.BuildNameToCertificate
// The nil value causes the first element of Certificates to be used
// for all connections.
NameToCertificate map[string]*Certificate
// GetCertificate returns a Certificate based on the given
// ClientHelloInfo. It will only be called if the client supplies SNI
// information or if Certificates is empty.
// If GetCertificate is nil or returns nil, then the certificate is
// retrieved from NameToCertificate. If NameToCertificate is nil, the
// first element of Certificates will be used.
GetCertificate func(*ClientHelloInfo) (*Certificate, error)
// GetClientCertificate, if not nil, is called when a server requests a
// certificate from a client. If set, the contents of Certificates will
// be ignored.
// If GetClientCertificate returns an error, the handshake will be
// aborted and that error will be returned. Otherwise
// GetClientCertificate must return a non-nil Certificate. If
// Certificate.Certificate is empty then no certificate will be sent to
// the server. If this is unacceptable to the server then it may abort
// the handshake.
// GetClientCertificate may be called multiple times for the same
// connection if renegotiation occurs or if TLS 1.3 is in use.
GetClientCertificate func(*CertificateRequestInfo) (*Certificate, error)
// GetConfigForClient, if not nil, is called after a ClientHello is
// received from a client. It may return a non-nil Config in order to
// change the Config that will be used to handle this connection. If
// the returned Config is nil, the original Config will be used. The
// Config returned by this callback may not be subsequently modified.
// If GetConfigForClient is nil, the Config passed to Server() will be
// used for all connections.
// Uniquely for the fields in the returned Config, session ticket keys
// will be duplicated from the original Config if not set.
// Specifically, if SetSessionTicketKeys was called on the original
// config but not on the returned config then the ticket keys from the
// original config will be copied into the new config before use.
// Otherwise, if SessionTicketKey was set in the original config but
// not in the returned config then it will be copied into the returned
// config before use. If neither of those cases applies then the key
// material from the returned config will be used for session tickets.
GetConfigForClient func(*ClientHelloInfo) (*Config, error)
// VerifyPeerCertificate, if not nil, is called after normal
// certificate verification by either a TLS client or server. It
// receives the raw ASN.1 certificates provided by the peer and also
// any verified chains that normal processing found. If it returns a
// non-nil error, the handshake is aborted and that error results.
// If normal verification fails then the handshake will abort before
// considering this callback. If normal verification is disabled by
// setting InsecureSkipVerify then this callback will be considered but
// the verifiedChains argument will always be nil.
VerifyPeerCertificate func(rawCerts [][]byte, verifiedChains [][]*x509.Certificate) error
// RootCAs defines the set of root certificate authorities
// that clients use when verifying server certificates.
// If RootCAs is nil, TLS uses the host's root CA set.
RootCAs *x509.CertPool
// NextProtos is a list of supported, application level protocols.
NextProtos []string
// ServerName is used to verify the hostname on the returned
// certificates unless InsecureSkipVerify is given. It is also included
// in the client's handshake to support virtual hosting unless it is
// an IP address.
ServerName string
// ClientAuth determines the server's policy for
// TLS Client Authentication. The default is NoClientCert.
ClientAuth ClientAuthType
// ClientCAs defines the set of root certificate authorities
// that servers use if required to verify a client certificate
// by the policy in ClientAuth.
ClientCAs *x509.CertPool
// InsecureSkipVerify controls whether a client verifies the
// server's certificate chain and host name.
// If InsecureSkipVerify is true, TLS accepts any certificate
// presented by the server and any host name in that certificate.
// In this mode, TLS is susceptible to man-in-the-middle attacks.
// This should be used only for testing.
InsecureSkipVerify bool
// CipherSuites is a list of supported cipher suites. If CipherSuites
// is nil, TLS uses a list of suites supported by the implementation.
CipherSuites []uint16
// PreferServerCipherSuites controls whether the server selects the
// client's most preferred ciphersuite, or the server's most preferred
// ciphersuite. If true then the server's preference, as expressed in
// the order of elements in CipherSuites, is used.
PreferServerCipherSuites bool
// SessionTicketsDisabled may be set to true to disable session ticket
// (resumption) support.
SessionTicketsDisabled bool
// SessionTicketKey is used by TLS servers to provide session
// resumption. See RFC 5077. If zero, it will be filled with
// random data before the first server handshake.
// If multiple servers are terminating connections for the same host
// they should all have the same SessionTicketKey. If the
// SessionTicketKey leaks, previously recorded and future TLS
// connections using that key are compromised.
SessionTicketKey [32]byte
// SessionCache is a cache of ClientSessionState entries for TLS session
// resumption.
ClientSessionCache ClientSessionCache
// MinVersion contains the minimum SSL/TLS version that is acceptable.
// If zero, then TLS 1.0 is taken as the minimum.
MinVersion uint16
// MaxVersion contains the maximum SSL/TLS version that is acceptable.
// If zero, then the maximum version supported by this package is used,
// which is currently TLS 1.2.
MaxVersion uint16
// CurvePreferences contains the elliptic curves that will be used in
// an ECDHE handshake, in preference order. If empty, the default will
// be used.
CurvePreferences []CurveID
// DynamicRecordSizingDisabled disables adaptive sizing of TLS records.
// When true, the largest possible TLS record size is always used. When
// false, the size of TLS records may be adjusted in an attempt to
// improve latency.
DynamicRecordSizingDisabled bool
// Renegotiation controls what types of renegotiation are supported.
// The default, none, is correct for the vast majority of applications.
Renegotiation RenegotiationSupport
// KeyLogWriter optionally specifies a destination for TLS master secrets
// in NSS key log format that can be used to allow external programs
// such as Wireshark to decrypt TLS connections.
// See
// Use of KeyLogWriter compromises security and should only be
// used for debugging.
KeyLogWriter io.Writer
serverInitOnce sync.Once // guards calling (*Config).serverInit
// mutex protects sessionTicketKeys.
mutex sync.RWMutex
// sessionTicketKeys contains zero or more ticket keys. If the length
// is zero, SessionTicketsDisabled must be true. The first key is used
// for new tickets and any subsequent keys can be used to decrypt old
// tickets.
sessionTicketKeys []ticketKey
// ticketKeyNameLen is the number of bytes of identifier that is prepended to
// an encrypted session ticket in order to identify the key used to encrypt it.
const ticketKeyNameLen = 16
// ticketKey is the internal representation of a session ticket key.
type ticketKey struct {
// keyName is an opaque byte string that serves to identify the session
// ticket key. It's exposed as plaintext in every session ticket.
keyName [ticketKeyNameLen]byte
aesKey [16]byte
hmacKey [16]byte
// ticketKeyFromBytes converts from the external representation of a session
// ticket key to a ticketKey. Externally, session ticket keys are 32 random
// bytes and this function expands that into sufficient name and key material.
func ticketKeyFromBytes(b [32]byte) (key ticketKey) {
hashed := sha512.Sum512(b[:])
copy(key.keyName[:], hashed[:ticketKeyNameLen])
copy(key.aesKey[:], hashed[ticketKeyNameLen:ticketKeyNameLen+16])
copy(key.hmacKey[:], hashed[ticketKeyNameLen+16:ticketKeyNameLen+32])
return key
// Clone returns a shallow clone of c. It is safe to clone a Config that is
// being used concurrently by a TLS client or server.
func (c *Config) Clone() *Config {
// Running serverInit ensures that it's safe to read
// SessionTicketsDisabled.
c.serverInitOnce.Do(func() { c.serverInit(nil) })
var sessionTicketKeys []ticketKey
sessionTicketKeys = c.sessionTicketKeys
return &Config{
Rand: c.Rand,
Time: c.Time,
Certificates: c.Certificates,
NameToCertificate: c.NameToCertificate,
GetCertificate: c.GetCertificate,
GetClientCertificate: c.GetClientCertificate,
GetConfigForClient: c.GetConfigForClient,
VerifyPeerCertificate: c.VerifyPeerCertificate,
RootCAs: c.RootCAs,
NextProtos: c.NextProtos,
ServerName: c.ServerName,
ClientAuth: c.ClientAuth,
ClientCAs: c.ClientCAs,
InsecureSkipVerify: c.InsecureSkipVerify,
CipherSuites: c.CipherSuites,
PreferServerCipherSuites: c.PreferServerCipherSuites,
SessionTicketsDisabled: c.SessionTicketsDisabled,
SessionTicketKey: c.SessionTicketKey,
ClientSessionCache: c.ClientSessionCache,
MinVersion: c.MinVersion,
MaxVersion: c.MaxVersion,
CurvePreferences: c.CurvePreferences,
DynamicRecordSizingDisabled: c.DynamicRecordSizingDisabled,
Renegotiation: c.Renegotiation,
KeyLogWriter: c.KeyLogWriter,
sessionTicketKeys: sessionTicketKeys,
// serverInit is run under c.serverInitOnce to do initialization of c. If c was
// returned by a GetConfigForClient callback then the argument should be the
// Config that was passed to Server, otherwise it should be nil.
func (c *Config) serverInit(originalConfig *Config) {
if c.SessionTicketsDisabled || len(c.ticketKeys()) != 0 {
alreadySet := false
for _, b := range c.SessionTicketKey {
if b != 0 {
alreadySet = true
if !alreadySet {
if originalConfig != nil {
copy(c.SessionTicketKey[:], originalConfig.SessionTicketKey[:])
} else if _, err := io.ReadFull(c.rand(), c.SessionTicketKey[:]); err != nil {
c.SessionTicketsDisabled = true
if originalConfig != nil {
c.sessionTicketKeys = originalConfig.sessionTicketKeys
} else {
c.sessionTicketKeys = []ticketKey{ticketKeyFromBytes(c.SessionTicketKey)}
func (c *Config) ticketKeys() []ticketKey {
// c.sessionTicketKeys is constant once created. SetSessionTicketKeys
// will only update it by replacing it with a new value.
ret := c.sessionTicketKeys
return ret
// SetSessionTicketKeys updates the session ticket keys for a server. The first
// key will be used when creating new tickets, while all keys can be used for
// decrypting tickets. It is safe to call this function while the server is
// running in order to rotate the session ticket keys. The function will panic
// if keys is empty.
func (c *Config) SetSessionTicketKeys(keys [][32]byte) {
if len(keys) == 0 {
panic("tls: keys must have at least one key")
newKeys := make([]ticketKey, len(keys))
for i, bytes := range keys {
newKeys[i] = ticketKeyFromBytes(bytes)
c.sessionTicketKeys = newKeys
func (c *Config) rand() io.Reader {
r := c.Rand
if r == nil {
return rand.Reader
return r
func (c *Config) time() time.Time {
t := c.Time
if t == nil {
t = time.Now
return t()
func (c *Config) cipherSuites() []uint16 {
if needFIPS() {
return fipsCipherSuites(c)
s := c.CipherSuites
if s == nil {
s = defaultCipherSuites()
return s
func (c *Config) minVersion() uint16 {
if needFIPS() {
return fipsMinVersion(c)
if c == nil || c.MinVersion == 0 {
return minVersion
return c.MinVersion
func (c *Config) maxVersion() uint16 {
if needFIPS() {
return fipsMaxVersion(c)
if c == nil || c.MaxVersion == 0 {
return maxVersion
return c.MaxVersion
var defaultCurvePreferences = []CurveID{X25519, CurveP256, CurveP384, CurveP521}
func (c *Config) curvePreferences() []CurveID {
if needFIPS() {
return fipsCurvePreferences(c)
if c == nil || len(c.CurvePreferences) == 0 {
return defaultCurvePreferences
return c.CurvePreferences
// mutualVersion returns the protocol version to use given the advertised
// version of the peer.
func (c *Config) mutualVersion(vers uint16) (uint16, bool) {
minVersion := c.minVersion()
maxVersion := c.maxVersion()
if vers < minVersion {
return 0, false
if vers > maxVersion {
vers = maxVersion
return vers, true
// getCertificate returns the best certificate for the given ClientHelloInfo,
// defaulting to the first element of c.Certificates.
func (c *Config) getCertificate(clientHello *ClientHelloInfo) (*Certificate, error) {
if c.GetCertificate != nil &&
(len(c.Certificates) == 0 || len(clientHello.ServerName) > 0) {
cert, err := c.GetCertificate(clientHello)
if cert != nil || err != nil {
return cert, err
if len(c.Certificates) == 0 {
return nil, errors.New("tls: no certificates configured")
if len(c.Certificates) == 1 || c.NameToCertificate == nil {
// There's only one choice, so no point doing any work.
return &c.Certificates[0], nil
name := strings.ToLower(clientHello.ServerName)
for len(name) > 0 && name[len(name)-1] == '.' {
name = name[:len(name)-1]
if cert, ok := c.NameToCertificate[name]; ok {
return cert, nil
// try replacing labels in the name with wildcards until we get a
// match.
labels := strings.Split(name, ".")
for i := range labels {
labels[i] = "*"
candidate := strings.Join(labels, ".")
if cert, ok := c.NameToCertificate[candidate]; ok {
return cert, nil
// If nothing matches, return the first certificate.
return &c.Certificates[0], nil
// BuildNameToCertificate parses c.Certificates and builds c.NameToCertificate
// from the CommonName and SubjectAlternateName fields of each of the leaf
// certificates.
func (c *Config) BuildNameToCertificate() {
c.NameToCertificate = make(map[string]*Certificate)
for i := range c.Certificates {
cert := &c.Certificates[i]
x509Cert, err := x509.ParseCertificate(cert.Certificate[0])
if err != nil {
if len(x509Cert.Subject.CommonName) > 0 {
c.NameToCertificate[x509Cert.Subject.CommonName] = cert
for _, san := range x509Cert.DNSNames {
c.NameToCertificate[san] = cert
// writeKeyLog logs client random and master secret if logging was enabled by
// setting c.KeyLogWriter.
func (c *Config) writeKeyLog(clientRandom, masterSecret []byte) error {
if c.KeyLogWriter == nil {
return nil
logLine := []byte(fmt.Sprintf("CLIENT_RANDOM %x %x\n", clientRandom, masterSecret))
_, err := c.KeyLogWriter.Write(logLine)
return err
// writerMutex protects all KeyLogWriters globally. It is rarely enabled,
// and is only for debugging, so a global mutex saves space.
var writerMutex sync.Mutex
// A Certificate is a chain of one or more certificates, leaf first.
type Certificate struct {
Certificate [][]byte
// PrivateKey contains the private key corresponding to the public key
// in Leaf. For a server, this must implement crypto.Signer and/or
// crypto.Decrypter, with an RSA or ECDSA PublicKey. For a client
// (performing client authentication), this must be a crypto.Signer
// with an RSA or ECDSA PublicKey.
PrivateKey crypto.PrivateKey
// OCSPStaple contains an optional OCSP response which will be served
// to clients that request it.
OCSPStaple []byte
// SignedCertificateTimestamps contains an optional list of Signed
// Certificate Timestamps which will be served to clients that request it.
SignedCertificateTimestamps [][]byte
// Leaf is the parsed form of the leaf certificate, which may be
// initialized using x509.ParseCertificate to reduce per-handshake
// processing for TLS clients doing client authentication. If nil, the
// leaf certificate will be parsed as needed.
Leaf *x509.Certificate
type handshakeMessage interface {
marshal() []byte
unmarshal([]byte) bool
// lruSessionCache is a ClientSessionCache implementation that uses an LRU
// caching strategy.
type lruSessionCache struct {
m map[string]*list.Element
q *list.List
capacity int
type lruSessionCacheEntry struct {
sessionKey string
state *ClientSessionState
// NewLRUClientSessionCache returns a ClientSessionCache with the given
// capacity that uses an LRU strategy. If capacity is < 1, a default capacity
// is used instead.
func NewLRUClientSessionCache(capacity int) ClientSessionCache {
const defaultSessionCacheCapacity = 64
if capacity < 1 {
capacity = defaultSessionCacheCapacity
return &lruSessionCache{
m: make(map[string]*list.Element),
q: list.New(),
capacity: capacity,
// Put adds the provided (sessionKey, cs) pair to the cache.
func (c *lruSessionCache) Put(sessionKey string, cs *ClientSessionState) {
defer c.Unlock()
if elem, ok := c.m[sessionKey]; ok {
entry := elem.Value.(*lruSessionCacheEntry)
entry.state = cs
if c.q.Len() < c.capacity {
entry := &lruSessionCacheEntry{sessionKey, cs}
c.m[sessionKey] = c.q.PushFront(entry)
elem := c.q.Back()
entry := elem.Value.(*lruSessionCacheEntry)
delete(c.m, entry.sessionKey)
entry.sessionKey = sessionKey
entry.state = cs
c.m[sessionKey] = elem
// Get returns the ClientSessionState value associated with a given key. It
// returns (nil, false) if no value is found.
func (c *lruSessionCache) Get(sessionKey string) (*ClientSessionState, bool) {
defer c.Unlock()
if elem, ok := c.m[sessionKey]; ok {
return elem.Value.(*lruSessionCacheEntry).state, true
return nil, false
// TODO(jsing): Make these available to both crypto/x509 and crypto/tls.
type dsaSignature struct {
R, S *big.Int
type ecdsaSignature dsaSignature
var emptyConfig Config
func defaultConfig() *Config {
return &emptyConfig
var (
once sync.Once
varDefaultCipherSuites []uint16
func defaultCipherSuites() []uint16 {
return varDefaultCipherSuites
func initDefaultCipherSuites() {
var topCipherSuites []uint16
if cipherhw.AESGCMSupport() {
// If AES-GCM hardware is provided then prioritise AES-GCM
// cipher suites.
topCipherSuites = []uint16{
} else {
// Without AES-GCM hardware, we put the ChaCha20-Poly1305
// cipher suites first.
topCipherSuites = []uint16{
varDefaultCipherSuites = make([]uint16, 0, len(cipherSuites))
varDefaultCipherSuites = append(varDefaultCipherSuites, topCipherSuites...)
for _, suite := range cipherSuites {
if suite.flags&suiteDefaultOff != 0 {
for _, existing := range varDefaultCipherSuites {
if existing == {
continue NextCipherSuite
varDefaultCipherSuites = append(varDefaultCipherSuites,
func unexpectedMessageError(wanted, got interface{}) error {
return fmt.Errorf("tls: received unexpected handshake message of type %T when waiting for %T", got, wanted)
func isSupportedSignatureAndHash(sigHash signatureAndHash, sigHashes []signatureAndHash) bool {
for _, s := range sigHashes {
if s == sigHash {
return true
return false