github.com/Hyperledger-TWGC/tjfoc-gm@v1.4.0/gmtls/common.go

/*Copyright Suzhou Tongji Fintech Research Institute 2017 All Rights Reserved.
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 gmtls

import (
	"container/list"
	"crypto"
	"crypto/rand"
	"crypto/sha512"
	"errors"
	"fmt"
	"github.com/Hyperledger-TWGC/tjfoc-gm/x509"
	"io"
	"math/big"
	"net"
	"strings"
	"sync"
	"time"
)

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)
	maxWarnAlertCount = 5            // maximum number of consecutive warning alerts

	minVersion = VersionGMSSL
	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 // https://tools.ietf.org/html/rfc6962#section-6
	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
// https://www.iana.org/assignments/tls-parameters/tls-parameters.xml#tls-parameters-8
type CurveID uint16

const (
	CurveP256 CurveID = 23
	CurveP384 CurveID = 24
	CurveP521 CurveID = 25
	X25519    CurveID = 29
)

// TLS Elliptic Curve Point Formats
// https://www.iana.org/assignments/tls-parameters/tls-parameters.xml#tls-parameters-9
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
)

// Signature algorithms (for internal signaling use). Starting at 16 to avoid overlap with
// TLS 1.2 codepoints (RFC 5246, section A.4.1), with which these have nothing to do.
const (
	signaturePKCS1v15 uint8 = iota + 16
	signatureECDSA
	signatureRSAPSS
	signatureSM2
)

// 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{
	PKCS1WithSHA256,
	ECDSAWithP256AndSHA256,
	PKCS1WithSHA384,
	ECDSAWithP384AndSHA384,
	PKCS1WithSHA512,
	ECDSAWithP521AndSHA512,
	PKCS1WithSHA1,
	ECDSAWithSHA1,
}

// 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

	// 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
	// https://mitls.org/pages/attacks/3SHAKE#channelbindings). This will
	// change in future versions of Go once the TLS master-secret fix has
	// been standardized and implemented.
	TLSUnique []byte
}

// ExportKeyingMaterial returns length bytes of exported key material in a new
// slice as defined in https://tools.ietf.org/html/rfc5705. 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
	RequestClientCert
	RequireAnyClientCert
	VerifyClientCertIfGiven
	RequireAndVerifyClientCert
)

// 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
// https://tools.ietf.org/html/draft-ietf-tls-tls13-18#section-4.2.3.
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

	// Legacy signature and hash algorithms for TLS 1.2.
	ECDSAWithSHA1 SignatureScheme = 0x0203
	SM2WITHSM3    SignatureScheme = 0x0204
)

// 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.
	// TLS_RSA_WITH_RC4_128_SHA).
	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
	// https://tools.ietf.org/html/rfc4366#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
	// https://tools.ietf.org/html/rfc4492#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
	// https://tools.ietf.org/html/rfc4492#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
	// https://tools.ietf.org/html/rfc5246#section-7.4.1.4.1).
	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
	// https://tools.ietf.org/html/rfc7301#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
// HTTPS.
type RenegotiationSupport int

const (
	// RenegotiateNever disables renegotiation.
	RenegotiateNever RenegotiationSupport = iota

	// RenegotiateOnceAsClient allows a remote server to request
	// renegotiation once per connection.
	RenegotiateOnceAsClient

	// RenegotiateFreelyAsClient allows a remote server to repeatedly
	// request renegotiation.
	RenegotiateFreelyAsClient
)

// 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 {
	//if not nil, will support GMT0024
	GMSupport *GMSupport

	// 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
	// '*.example.com' 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.
	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. 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. 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

	// 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 1.2.
	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 https://developer.mozilla.org/en-US/docs/Mozilla/Projects/NSS/Key_Log_Format.
	// 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
	c.mutex.RLock()
	sessionTicketKeys = c.sessionTicketKeys
	c.mutex.RUnlock()

	return &Config{
		GMSupport:                   c.GMSupport,
		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 {
		return
	}

	alreadySet := false
	for _, b := range c.SessionTicketKey {
		if b != 0 {
			alreadySet = true
			break
		}
	}

	if !alreadySet {
		if originalConfig != nil {
			copy(c.SessionTicketKey[:], originalConfig.SessionTicketKey[:])
		} else if _, err := io.ReadFull(c.rand(), c.SessionTicketKey[:]); err != nil {
			c.SessionTicketsDisabled = true
			return
		}
	}

	if originalConfig != nil {
		originalConfig.mutex.RLock()
		c.sessionTicketKeys = originalConfig.sessionTicketKeys
		originalConfig.mutex.RUnlock()
	} else {
		c.sessionTicketKeys = []ticketKey{ticketKeyFromBytes(c.SessionTicketKey)}
	}
}

func (c *Config) ticketKeys() []ticketKey {
	c.mutex.RLock()
	// c.sessionTicketKeys is constant once created. SetSessionTicketKeys
	// will only update it by replacing it with a new value.
	ret := c.sessionTicketKeys
	c.mutex.RUnlock()
	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.mutex.Lock()
	c.sessionTicketKeys = newKeys
	c.mutex.Unlock()
}

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
}

func (c *Config) minVersion() uint16 {
	if c == nil || c.MinVersion == 0 {
		return minVersion
	}
	return c.MinVersion
}

func (c *Config) maxVersion() uint16 {
	if c == nil || c.MaxVersion == 0 {
		return maxVersion
	}
	return c.MaxVersion
}

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
// 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 {
			continue
		}
		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))

	writerMutex.Lock()
	_, err := c.KeyLogWriter.Write(logLine)
	writerMutex.Unlock()

	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 {
	sync.Mutex

	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) {
	c.Lock()
	defer c.Unlock()

	if elem, ok := c.m[sessionKey]; ok {
		entry := elem.Value.(*lruSessionCacheEntry)
		entry.state = cs
		c.q.MoveToFront(elem)
		return
	}

	if c.q.Len() < c.capacity {
		entry := &lruSessionCacheEntry{sessionKey, cs}
		c.m[sessionKey] = c.q.PushFront(entry)
		return
	}

	elem := c.q.Back()
	entry := elem.Value.(*lruSessionCacheEntry)
	delete(c.m, entry.sessionKey)
	entry.sessionKey = sessionKey
	entry.state = cs
	c.q.MoveToFront(elem)
	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) {
	c.Lock()
	defer c.Unlock()

	if elem, ok := c.m[sessionKey]; ok {
		c.q.MoveToFront(elem)
		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 {
	once.Do(initDefaultCipherSuites)
	return varDefaultCipherSuites
}

func initDefaultCipherSuites() {
	// Without AES-GCM hardware, we put the ChaCha20-Poly1305
	// cipher suites first.
	topCipherSuites := []uint16{
		TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305,
		TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305,
		TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256,
		TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384,
		TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256,
		TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384,
	}

	varDefaultCipherSuites = make([]uint16, 0, len(cipherSuites))
	varDefaultCipherSuites = append(varDefaultCipherSuites, topCipherSuites...)

NextCipherSuite:
	for _, suite := range cipherSuites {
		if suite.flags&suiteDefaultOff != 0 {
			continue
		}
		for _, existing := range varDefaultCipherSuites {
			if existing == suite.id {
				continue NextCipherSuite
			}
		}
		varDefaultCipherSuites = append(varDefaultCipherSuites, suite.id)
	}
}

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
	default:
		return 0
	}
}