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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
VersionTLS13 = 0x0304
const (
maxPlaintext = 16384 // maximum plaintext payload length
maxCiphertext = 16384 + 2048 // maximum ciphertext payload length
maxCiphertextTLS13 = 16384 + 256 // maximum ciphertext length in TLS 1.3
recordHeaderLen = 5 // record header length
maxHandshake = 65536 // maximum handshake we support (protocol max is 16 MB)
maxUselessRecords = 16 // maximum number of consecutive non-advancing records
// 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
typeEndOfEarlyData uint8 = 5
typeEncryptedExtensions uint8 = 8
typeCertificate uint8 = 11
typeServerKeyExchange uint8 = 12
typeCertificateRequest uint8 = 13
typeServerHelloDone uint8 = 14
typeCertificateVerify uint8 = 15
typeClientKeyExchange uint8 = 16
typeFinished uint8 = 20
typeCertificateStatus uint8 = 22
typeKeyUpdate uint8 = 24
typeNextProtocol uint8 = 67 // Not IANA assigned
typeMessageHash uint8 = 254 // synthetic message
// TLS compression types.
const (
compressionNone uint8 = 0
// TLS extension numbers
const (
extensionServerName uint16 = 0
extensionStatusRequest uint16 = 5
extensionSupportedCurves uint16 = 10 // supported_groups in TLS 1.3, see RFC 8446, Section 4.2.7
extensionSupportedPoints uint16 = 11
extensionSignatureAlgorithms uint16 = 13
extensionALPN uint16 = 16
extensionSCT uint16 = 18
extensionSessionTicket uint16 = 35
extensionPreSharedKey uint16 = 41
extensionEarlyData uint16 = 42
extensionSupportedVersions uint16 = 43
extensionCookie uint16 = 44
extensionPSKModes uint16 = 45
extensionCertificateAuthorities uint16 = 47
extensionSignatureAlgorithmsCert uint16 = 50
extensionKeyShare uint16 = 51
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
// In TLS 1.3, this type is called NamedGroup, but at this time this library
// only supports Elliptic Curve based groups. See RFC 8446, Section 4.2.7.
type CurveID uint16
const (
CurveP256 CurveID = 23
CurveP384 CurveID = 24
CurveP521 CurveID = 25
X25519 CurveID = 29
// TLS 1.3 Key Share. See RFC 8446, Section 4.2.8.
type keyShare struct {
group CurveID
data []byte
// TLS 1.3 PSK Key Exchange Modes. See RFC 8446, Section 4.2.9.
const (
pskModePlain uint8 = 0
pskModeDHE uint8 = 1
// TLS 1.3 PSK Identity. Can be a Session Ticket, or a reference to a saved
// session. See RFC 8446, Section 4.2.11.
type pskIdentity struct {
label []byte
obfuscatedTicketAge uint32
// TLS Elliptic Curve Point Formats
const (
pointFormatUncompressed uint8 = 0
// TLS CertificateStatusType (RFC 3546)
const (
statusTypeOCSP uint8 = 1
// Certificate types (for certificateRequestMsg)
const (
certTypeRSASign = 1
certTypeECDSASign = 64 // RFC 4492, Section 5.5
// Signature algorithms (for internal signaling use). Starting at 16 to avoid overlap with
// TLS 1.2 codepoints (RFC 5246, Appendix A.4.1), with which these have nothing to do.
const (
signaturePKCS1v15 uint8 = iota + 16
// supportedSignatureAlgorithms 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. The two fields are merged to match with TLS 1.3.
// Note that in TLS 1.2, the ECDSA algorithms are not constrained to P-256, etc.
var supportedSignatureAlgorithms = []SignatureScheme{
// helloRetryRequestRandom is set as the Random value of a ServerHello
// to signal that the message is actually a HelloRetryRequest.
var helloRetryRequestRandom = []byte{ // See RFC 8446, Section 4.1.3.
0xCF, 0x21, 0xAD, 0x74, 0xE5, 0x9A, 0x61, 0x11,
0xBE, 0x1D, 0x8C, 0x02, 0x1E, 0x65, 0xB8, 0x91,
0xC2, 0xA2, 0x11, 0x16, 0x7A, 0xBB, 0x8C, 0x5E,
0x07, 0x9E, 0x09, 0xE2, 0xC8, 0xA8, 0x33, 0x9C,
const (
// downgradeCanaryTLS12 or downgradeCanaryTLS11 is embedded in the server
// random as a downgrade protection if the server would be capable of
// negotiating a higher version. See RFC 8446, Section 4.1.3.
downgradeCanaryTLS12 = "DOWNGRD\x01"
downgradeCanaryTLS11 = "DOWNGRD\x00"
// 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 peer, if any
OCSPResponse []byte // stapled OCSP response from peer, if any
// ekm is a closure exposed via ExportKeyingMaterial.
ekm func(label string, context []byte, length int) ([]byte, error)
// 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. It is not defined in TLS 1.3.
TLSUnique []byte
// ExportKeyingMaterial returns length bytes of exported key material in a new
// slice as defined in RFC 5705. If context is nil, it is not used as part of
// the seed. If the connection was set to allow renegotiation via
// Config.Renegotiation, this function will return an error.
func (cs *ConnectionState) ExportKeyingMaterial(label string, context []byte, length int) ([]byte, error) {
return cs.ekm(label, context, length)
// ClientAuthType declares the policy the server will follow for
// TLS Client Authentication.
type ClientAuthType int
const (
NoClientCert ClientAuthType = iota
// requiresClientCert returns whether the ClientAuthType requires a client
// certificate to be provided.
func requiresClientCert(c ClientAuthType) bool {
switch c {
case RequireAnyClientCert, RequireAndVerifyClientCert:
return true
return false
// 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 // Full handshake MasterSecret, or TLS 1.3 resumption_master_secret
serverCertificates []*x509.Certificate // Certificate chain presented by the server
verifiedChains [][]*x509.Certificate // Certificate chains we built for verification
receivedAt time.Time // When the session ticket was received from the server
// TLS 1.3 fields.
nonce []byte // Ticket nonce sent by the server, to derive PSK
useBy time.Time // Expiration of the ticket lifetime as set by the server
ageAdd uint32 // Random obfuscation factor for sending the ticket age
// 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. Up to TLS 1.2, only ticket-based resumption is supported, not
// SessionID-based resumption. In TLS 1.3 they were merged into PSK modes, which
// are supported via this interface.
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. It might
// get called multiple times in a connection if a TLS 1.3 server provides
// more than one session ticket. If called with a nil *ClientSessionState,
// it should remove the cache entry.
Put(sessionKey string, cs *ClientSessionState)
// SignatureScheme identifies a signature algorithm supported by TLS. See
// RFC 8446, Section 4.2.3.
type SignatureScheme uint16
const (
PKCS1WithSHA1 SignatureScheme = 0x0201
PKCS1WithSHA256 SignatureScheme = 0x0401
PKCS1WithSHA384 SignatureScheme = 0x0501
PKCS1WithSHA512 SignatureScheme = 0x0601
// RSASSA-PSS algorithms with public key OID rsaEncryption.
PSSWithSHA256 SignatureScheme = 0x0804
PSSWithSHA384 SignatureScheme = 0x0805
PSSWithSHA512 SignatureScheme = 0x0806
ECDSAWithP256AndSHA256 SignatureScheme = 0x0403
ECDSAWithP384AndSHA384 SignatureScheme = 0x0503
ECDSAWithP521AndSHA512 SignatureScheme = 0x0603
// Legacy signature and hash algorithms for TLS 1.2.
ECDSAWithSHA1 SignatureScheme = 0x0203
// 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 RFC 4366, Section 3.1).
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 RFC 4492, Section 5.1.1).
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 RFC 4492, Section 5.1.2).
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 RFC 5246, Section
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 RFC 7301, Section 3.1).
// 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
// Renegotiation is not defined in TLS 1.3.
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, or (for a server) when ClientAuth is
// RequestClientCert or RequireAnyClientCert, 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, in
// order of preference.
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 and
// PSK (resumption) support. Note that on clients, session ticket support is
// also disabled if ClientSessionCache is nil.
SessionTicketsDisabled bool
// SessionTicketKey is used by TLS servers to provide session resumption.
// See RFC 5077 and the PSK mode of RFC 8446. 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 might be compromised.
SessionTicketKey [32]byte
// ClientSessionCache is a cache of ClientSessionState entries for TLS
// session resumption. It is only used by clients.
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 1.3.
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. The client will use the first preference as the type for
// its key share in TLS 1.3. This may change in the future.
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
// maxSessionTicketLifetime is the maximum allowed lifetime of a TLS 1.3 session
// ticket, and the lifetime we set for tickets we send.
const maxSessionTicketLifetime = 7 * 24 * time.Hour
// 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 {
s := c.CipherSuites
if s == nil {
s = defaultCipherSuites()
return s
var supportedVersions = []uint16{
func (c *Config) supportedVersions(isClient bool) []uint16 {
versions := make([]uint16, 0, len(supportedVersions))
for _, v := range supportedVersions {
if c != nil && c.MinVersion != 0 && v < c.MinVersion {
if c != nil && c.MaxVersion != 0 && v > c.MaxVersion {
// TLS 1.0 is the minimum version supported as a client.
if isClient && v < VersionTLS10 {
versions = append(versions, v)
return versions
func (c *Config) maxSupportedVersion(isClient bool) uint16 {
supportedVersions := c.supportedVersions(isClient)
if len(supportedVersions) == 0 {
return 0
return supportedVersions[0]
// supportedVersionsFromMax returns a list of supported versions derived from a
// legacy maximum version value. Note that only versions supported by this
// library are returned. Any newer peer will use supportedVersions anyway.
func supportedVersionsFromMax(maxVersion uint16) []uint16 {
versions := make([]uint16, 0, len(supportedVersions))
for _, v := range supportedVersions {
if v > maxVersion {
versions = append(versions, v)
return versions
var defaultCurvePreferences = []CurveID{X25519, CurveP256, CurveP384, CurveP521}
func (c *Config) curvePreferences() []CurveID {
if c == nil || len(c.CurvePreferences) == 0 {
return defaultCurvePreferences
return c.CurvePreferences
// mutualVersion returns the protocol version to use given the advertised
// versions of the peer. Priority is given to the peer preference order.
func (c *Config) mutualVersion(isClient bool, peerVersions []uint16) (uint16, bool) {
supportedVersions := c.supportedVersions(isClient)
for _, peerVersion := range peerVersions {
for _, v := range supportedVersions {
if v == peerVersion {
return v, true
return 0, false
// 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 := cert.Leaf
if x509Cert == nil {
var err error
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
const (
keyLogLabelTLS12 = "CLIENT_RANDOM"
keyLogLabelClientTraffic = "CLIENT_TRAFFIC_SECRET_0"
keyLogLabelServerTraffic = "SERVER_TRAFFIC_SECRET_0"
func (c *Config) writeKeyLog(label string, clientRandom, secret []byte) error {
if c.KeyLogWriter == nil {
return nil
logLine := []byte(fmt.Sprintf("%s %x %x\n", label, clientRandom, secret))
_, 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. If cs is nil, the entry
// corresponding to sessionKey is removed from the cache instead.
func (c *lruSessionCache) Put(sessionKey string, cs *ClientSessionState) {
defer c.Unlock()
if elem, ok := c.m[sessionKey]; ok {
if cs == nil {
delete(c.m, sessionKey)
} else {
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
varDefaultCipherSuitesTLS13 []uint16
func defaultCipherSuites() []uint16 {
return varDefaultCipherSuites
func defaultCipherSuitesTLS13() []uint16 {
return varDefaultCipherSuitesTLS13
func initDefaultCipherSuites() {
var topCipherSuites []uint16
// Check the cpu flags for each platform that has optimized GCM implementations.
// Worst case, these variables will just all be false.
var (
hasGCMAsmAMD64 = cpu.X86.HasAES && cpu.X86.HasPCLMULQDQ
hasGCMAsmARM64 = cpu.ARM64.HasAES && cpu.ARM64.HasPMULL
// Keep in sync with crypto/aes/cipher_s390x.go.
// hasGCMAsmS390X = cpu.S390X.HasAES && cpu.S390X.HasAESCBC && cpu.S390X.HasAESCTR && (cpu.S390X.HasGHASH || cpu.S390X.HasAESGCM)
hasGCMAsmS390X = false // [UTLS: couldn't be bothered to make it work, we won't use it]
hasGCMAsm = hasGCMAsmAMD64 || hasGCMAsmARM64 || hasGCMAsmS390X
if hasGCMAsm {
// If AES-GCM hardware is provided then prioritise AES-GCM
// cipher suites.
topCipherSuites = []uint16{
varDefaultCipherSuitesTLS13 = []uint16{
} else {
// Without AES-GCM hardware, we put the ChaCha20-Poly1305
// cipher suites first.
topCipherSuites = []uint16{
varDefaultCipherSuitesTLS13 = []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 isSupportedSignatureAlgorithm(sigAlg SignatureScheme, supportedSignatureAlgorithms []SignatureScheme) bool {
for _, s := range supportedSignatureAlgorithms {
if s == sigAlg {
return true
return false
// signatureFromSignatureScheme maps a signature algorithm to the underlying
// signature method (without hash function).
func signatureFromSignatureScheme(signatureAlgorithm SignatureScheme) uint8 {
switch signatureAlgorithm {
case PKCS1WithSHA1, PKCS1WithSHA256, PKCS1WithSHA384, PKCS1WithSHA512:
return signaturePKCS1v15
case PSSWithSHA256, PSSWithSHA384, PSSWithSHA512:
return signatureRSAPSS
case ECDSAWithSHA1, ECDSAWithP256AndSHA256, ECDSAWithP384AndSHA384, ECDSAWithP521AndSHA512:
return signatureECDSA
return 0
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