src/crypto/tls/prf.go - go - Git at Google

 // 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 (
 	"crypto"
 	"crypto/hmac"
 	"crypto/md5"
 	"crypto/sha1"
 	"crypto/sha256"
 	"crypto/sha512"
 	"errors"
 	"fmt"
 	"hash"
 )

 // Split a premaster secret in two as specified in RFC 4346, Section 5.
 func splitPreMasterSecret(secret []byte) (s1, s2 []byte) {
 	s1 = secret[0 : (len(secret)+1)/2]
 	s2 = secret[len(secret)/2:]
 	return
 }

 // pHash implements the P_hash function, as defined in RFC 4346, Section 5.
 func pHash(result, secret, seed []byte, hash func() hash.Hash) {
 	h := hmac.New(hash, secret)
 	h.Write(seed)
 	a := h.Sum(nil)

 	j := 0
 	for j < len(result) {
 		h.Reset()
 		h.Write(a)
 		h.Write(seed)
 		b := h.Sum(nil)
 		copy(result[j:], b)
 		j += len(b)

 		h.Reset()
 		h.Write(a)
 		a = h.Sum(nil)
 	}
 }

 // prf10 implements the TLS 1.0 pseudo-random function, as defined in RFC 2246, Section 5.
 func prf10(result, secret, label, seed []byte) {
 	hashSHA1 := sha1.New
 	hashMD5 := md5.New

 	labelAndSeed := make([]byte, len(label)+len(seed))
 	copy(labelAndSeed, label)
 	copy(labelAndSeed[len(label):], seed)

 	s1, s2 := splitPreMasterSecret(secret)
 	pHash(result, s1, labelAndSeed, hashMD5)
 	result2 := make([]byte, len(result))
 	pHash(result2, s2, labelAndSeed, hashSHA1)

 	for i, b := range result2 {
 		result[i] ^= b
 	}
 }

 // prf12 implements the TLS 1.2 pseudo-random function, as defined in RFC 5246, Section 5.
 func prf12(hashFunc func() hash.Hash) func(result, secret, label, seed []byte) {
 	return func(result, secret, label, seed []byte) {
 		labelAndSeed := make([]byte, len(label)+len(seed))
 		copy(labelAndSeed, label)
 		copy(labelAndSeed[len(label):], seed)

 		pHash(result, secret, labelAndSeed, hashFunc)
 	}
 }

 // prf30 implements the SSL 3.0 pseudo-random function, as defined in
 // www.mozilla.org/projects/security/pki/nss/ssl/draft302.txt section 6.
 func prf30(result, secret, label, seed []byte) {
 	hashSHA1 := sha1.New()
 	hashMD5 := md5.New()

 	done := 0
 	i := 0
 	// RFC 5246 section 6.3 says that the largest PRF output needed is 128
 	// bytes. Since no more ciphersuites will be added to SSLv3, this will
 	// remain true. Each iteration gives us 16 bytes so 10 iterations will
 	// be sufficient.
 	var b [11]byte
 	for done < len(result) {
 		for j := 0; j <= i; j++ {
 			b[j] = 'A' + byte(i)
 		}

 		hashSHA1.Reset()
 		hashSHA1.Write(b[:i+1])
 		hashSHA1.Write(secret)
 		hashSHA1.Write(seed)
 		digest := hashSHA1.Sum(nil)

 		hashMD5.Reset()
 		hashMD5.Write(secret)
 		hashMD5.Write(digest)

 		done += copy(result[done:], hashMD5.Sum(nil))
 		i++
 	}
 }

 const (
 	masterSecretLength   = 48 // Length of a master secret in TLS 1.1.
 	finishedVerifyLength = 12 // Length of verify_data in a Finished message.
 )

 var masterSecretLabel = []byte("master secret")
 var keyExpansionLabel = []byte("key expansion")
 var clientFinishedLabel = []byte("client finished")
 var serverFinishedLabel = []byte("server finished")

 func prfAndHashForVersion(version uint16, suite *cipherSuite) (func(result, secret, label, seed []byte), crypto.Hash) {
 	switch version {
 	case VersionSSL30:
 		return prf30, crypto.Hash(0)
 	case VersionTLS10, VersionTLS11:
 		return prf10, crypto.Hash(0)
 	case VersionTLS12:
 		if suite.flags&suiteSHA384 != 0 {
 			return prf12(sha512.New384), crypto.SHA384
 		}
 		return prf12(sha256.New), crypto.SHA256
 	default:
 		panic("unknown version")
 	}
 }

 func prfForVersion(version uint16, suite *cipherSuite) func(result, secret, label, seed []byte) {
 	prf, _ := prfAndHashForVersion(version, suite)
 	return prf
 }

 // masterFromPreMasterSecret generates the master secret from the pre-master
 // secret. See RFC 5246, Section 8.1.
 func masterFromPreMasterSecret(version uint16, suite *cipherSuite, preMasterSecret, clientRandom, serverRandom []byte) []byte {
 	seed := make([]byte, 0, len(clientRandom)+len(serverRandom))
 	seed = append(seed, clientRandom...)
 	seed = append(seed, serverRandom...)

 	masterSecret := make([]byte, masterSecretLength)
 	prfForVersion(version, suite)(masterSecret, preMasterSecret, masterSecretLabel, seed)
 	return masterSecret
 }

 // keysFromMasterSecret generates the connection keys from the master
 // secret, given the lengths of the MAC key, cipher key and IV, as defined in
 // RFC 2246, Section 6.3.
 func keysFromMasterSecret(version uint16, suite *cipherSuite, masterSecret, clientRandom, serverRandom []byte, macLen, keyLen, ivLen int) (clientMAC, serverMAC, clientKey, serverKey, clientIV, serverIV []byte) {
 	seed := make([]byte, 0, len(serverRandom)+len(clientRandom))
 	seed = append(seed, serverRandom...)
 	seed = append(seed, clientRandom...)

 	n := 2*macLen + 2*keyLen + 2*ivLen
 	keyMaterial := make([]byte, n)
 	prfForVersion(version, suite)(keyMaterial, masterSecret, keyExpansionLabel, seed)
 	clientMAC = keyMaterial[:macLen]
 	keyMaterial = keyMaterial[macLen:]
 	serverMAC = keyMaterial[:macLen]
 	keyMaterial = keyMaterial[macLen:]
 	clientKey = keyMaterial[:keyLen]
 	keyMaterial = keyMaterial[keyLen:]
 	serverKey = keyMaterial[:keyLen]
 	keyMaterial = keyMaterial[keyLen:]
 	clientIV = keyMaterial[:ivLen]
 	keyMaterial = keyMaterial[ivLen:]
 	serverIV = keyMaterial[:ivLen]
 	return
 }

 // hashFromSignatureScheme returns the corresponding crypto.Hash for a given
 // hash from a TLS SignatureScheme.
 func hashFromSignatureScheme(signatureAlgorithm SignatureScheme) (crypto.Hash, error) {
 	switch signatureAlgorithm {
 	case PKCS1WithSHA1, ECDSAWithSHA1:
 		return crypto.SHA1, nil
 	case PKCS1WithSHA256, PSSWithSHA256, ECDSAWithP256AndSHA256:
 		return crypto.SHA256, nil
 	case PKCS1WithSHA384, PSSWithSHA384, ECDSAWithP384AndSHA384:
 		return crypto.SHA384, nil
 	case PKCS1WithSHA512, PSSWithSHA512, ECDSAWithP521AndSHA512:
 		return crypto.SHA512, nil
 	case Ed25519:
 		return directSigning, nil
 	default:
 		return 0, fmt.Errorf("tls: unsupported signature algorithm: %#04x", signatureAlgorithm)
 	}
 }

 func newFinishedHash(version uint16, cipherSuite *cipherSuite) finishedHash {
 	var buffer []byte
 	if version == VersionSSL30 || version >= VersionTLS12 {
 		buffer = []byte{}
 	}

 	prf, hash := prfAndHashForVersion(version, cipherSuite)
 	if hash != 0 {
 		return finishedHash{hash.New(), hash.New(), nil, nil, buffer, version, prf}
 	}

 	return finishedHash{sha1.New(), sha1.New(), md5.New(), md5.New(), buffer, version, prf}
 }

 // A finishedHash calculates the hash of a set of handshake messages suitable
 // for including in a Finished message.
 type finishedHash struct {
 	client hash.Hash
 	server hash.Hash

 	// Prior to TLS 1.2, an additional MD5 hash is required.
 	clientMD5 hash.Hash
 	serverMD5 hash.Hash

 	// In TLS 1.2, a full buffer is sadly required.
 	buffer []byte

 	version uint16
 	prf     func(result, secret, label, seed []byte)
 }

 func (h *finishedHash) Write(msg []byte) (n int, err error) {
 	h.client.Write(msg)
 	h.server.Write(msg)

 	if h.version < VersionTLS12 {
 		h.clientMD5.Write(msg)
 		h.serverMD5.Write(msg)
 	}

 	if h.buffer != nil {
 		h.buffer = append(h.buffer, msg...)
 	}

 	return len(msg), nil
 }

 func (h finishedHash) Sum() []byte {
 	if h.version >= VersionTLS12 {
 		return h.client.Sum(nil)
 	}

 	out := make([]byte, 0, md5.Size+sha1.Size)
 	out = h.clientMD5.Sum(out)
 	return h.client.Sum(out)
 }

 // finishedSum30 calculates the contents of the verify_data member of a SSLv3
 // Finished message given the MD5 and SHA1 hashes of a set of handshake
 // messages.
 func finishedSum30(md5, sha1 hash.Hash, masterSecret []byte, magic []byte) []byte {
 	md5.Write(magic)
 	md5.Write(masterSecret)
 	md5.Write(ssl30Pad1[:])
 	md5Digest := md5.Sum(nil)

 	md5.Reset()
 	md5.Write(masterSecret)
 	md5.Write(ssl30Pad2[:])
 	md5.Write(md5Digest)
 	md5Digest = md5.Sum(nil)

 	sha1.Write(magic)
 	sha1.Write(masterSecret)
 	sha1.Write(ssl30Pad1[:40])
 	sha1Digest := sha1.Sum(nil)

 	sha1.Reset()
 	sha1.Write(masterSecret)
 	sha1.Write(ssl30Pad2[:40])
 	sha1.Write(sha1Digest)
 	sha1Digest = sha1.Sum(nil)

 	ret := make([]byte, len(md5Digest)+len(sha1Digest))
 	copy(ret, md5Digest)
 	copy(ret[len(md5Digest):], sha1Digest)
 	return ret
 }

 var ssl3ClientFinishedMagic = [4]byte{0x43, 0x4c, 0x4e, 0x54}
 var ssl3ServerFinishedMagic = [4]byte{0x53, 0x52, 0x56, 0x52}

 // clientSum returns the contents of the verify_data member of a client's
 // Finished message.
 func (h finishedHash) clientSum(masterSecret []byte) []byte {
 	if h.version == VersionSSL30 {
 		return finishedSum30(h.clientMD5, h.client, masterSecret, ssl3ClientFinishedMagic[:])
 	}

 	out := make([]byte, finishedVerifyLength)
 	h.prf(out, masterSecret, clientFinishedLabel, h.Sum())
 	return out
 }

 // serverSum returns the contents of the verify_data member of a server's
 // Finished message.
 func (h finishedHash) serverSum(masterSecret []byte) []byte {
 	if h.version == VersionSSL30 {
 		return finishedSum30(h.serverMD5, h.server, masterSecret, ssl3ServerFinishedMagic[:])
 	}

 	out := make([]byte, finishedVerifyLength)
 	h.prf(out, masterSecret, serverFinishedLabel, h.Sum())
 	return out
 }

 // hashForClientCertificate returns the handshake messages so far, pre-hashed if
 // necessary, suitable for signing by a TLS client certificate.
 func (h finishedHash) hashForClientCertificate(sigType uint8, hashAlg crypto.Hash, masterSecret []byte) ([]byte, error) {
 	if (h.version == VersionSSL30 || h.version >= VersionTLS12 || sigType == signatureEd25519) && h.buffer == nil {
 		panic("tls: handshake hash for a client certificate requested after discarding the handshake buffer")
 	}

 	if h.version == VersionSSL30 {
 		if sigType != signaturePKCS1v15 {
 			return nil, errors.New("tls: unsupported signature type for client certificate")
 		}

 		md5Hash := md5.New()
 		md5Hash.Write(h.buffer)
 		sha1Hash := sha1.New()
 		sha1Hash.Write(h.buffer)
 		return finishedSum30(md5Hash, sha1Hash, masterSecret, nil), nil
 	}

 	if sigType == signatureEd25519 {
 		return h.buffer, nil
 	}

 	if h.version >= VersionTLS12 {
 		hash := hashAlg.New()
 		hash.Write(h.buffer)
 		return hash.Sum(nil), nil
 	}

 	if sigType == signatureECDSA {
 		return h.server.Sum(nil), nil
 	}

 	return h.Sum(), nil
 }

 // discardHandshakeBuffer is called when there is no more need to
 // buffer the entirety of the handshake messages.
 func (h *finishedHash) discardHandshakeBuffer() {
 	h.buffer = nil
 }

 // noExportedKeyingMaterial is used as a value of
 // ConnectionState.ekm when renegotation is enabled and thus
 // we wish to fail all key-material export requests.
 func noExportedKeyingMaterial(label string, context []byte, length int) ([]byte, error) {
 	return nil, errors.New("crypto/tls: ExportKeyingMaterial is unavailable when renegotiation is enabled")
 }

 // ekmFromMasterSecret generates exported keying material as defined in RFC 5705.
 func ekmFromMasterSecret(version uint16, suite *cipherSuite, masterSecret, clientRandom, serverRandom []byte) func(string, []byte, int) ([]byte, error) {
 	return func(label string, context []byte, length int) ([]byte, error) {
 		switch label {
 		case "client finished", "server finished", "master secret", "key expansion":
 			// These values are reserved and may not be used.
 			return nil, fmt.Errorf("crypto/tls: reserved ExportKeyingMaterial label: %s", label)
 		}

 		seedLen := len(serverRandom) + len(clientRandom)
 		if context != nil {
 			seedLen += 2 + len(context)
 		}
 		seed := make([]byte, 0, seedLen)

 		seed = append(seed, clientRandom...)
 		seed = append(seed, serverRandom...)

 		if context != nil {
 			if len(context) >= 1<<16 {
 				return nil, fmt.Errorf("crypto/tls: ExportKeyingMaterial context too long")
 			}
 			seed = append(seed, byte(len(context)>>8), byte(len(context)))
 			seed = append(seed, context...)
 		}

 		keyMaterial := make([]byte, length)
 		prfForVersion(version, suite)(keyMaterial, masterSecret, []byte(label), seed)
 		return keyMaterial, nil
 	}
 }
	// 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 (
	"crypto"
	"crypto/hmac"
	"crypto/md5"
	"crypto/sha1"
	"crypto/sha256"
	"crypto/sha512"
	"errors"
	"fmt"
	"hash"
	)

	// Split a premaster secret in two as specified in RFC 4346, Section 5.
	func splitPreMasterSecret(secret []byte) (s1, s2 []byte) {
	s1 = secret[0 : (len(secret)+1)/2]
	s2 = secret[len(secret)/2:]
	return
	}

	// pHash implements the P_hash function, as defined in RFC 4346, Section 5.
	func pHash(result, secret, seed []byte, hash func() hash.Hash) {
	h := hmac.New(hash, secret)
	h.Write(seed)
	a := h.Sum(nil)

	j := 0
	for j < len(result) {
	h.Reset()
	h.Write(a)
	h.Write(seed)
	b := h.Sum(nil)
	copy(result[j:], b)
	j += len(b)

	h.Reset()
	h.Write(a)
	a = h.Sum(nil)
	}
	}

	// prf10 implements the TLS 1.0 pseudo-random function, as defined in RFC 2246, Section 5.
	func prf10(result, secret, label, seed []byte) {
	hashSHA1 := sha1.New
	hashMD5 := md5.New

	labelAndSeed := make([]byte, len(label)+len(seed))
	copy(labelAndSeed, label)
	copy(labelAndSeed[len(label):], seed)

	s1, s2 := splitPreMasterSecret(secret)
	pHash(result, s1, labelAndSeed, hashMD5)
	result2 := make([]byte, len(result))
	pHash(result2, s2, labelAndSeed, hashSHA1)

	for i, b := range result2 {
	result[i] ^= b
	}
	}

	// prf12 implements the TLS 1.2 pseudo-random function, as defined in RFC 5246, Section 5.
	func prf12(hashFunc func() hash.Hash) func(result, secret, label, seed []byte) {
	return func(result, secret, label, seed []byte) {
	labelAndSeed := make([]byte, len(label)+len(seed))
	copy(labelAndSeed, label)
	copy(labelAndSeed[len(label):], seed)

	pHash(result, secret, labelAndSeed, hashFunc)
	}
	}

	// prf30 implements the SSL 3.0 pseudo-random function, as defined in
	// www.mozilla.org/projects/security/pki/nss/ssl/draft302.txt section 6.
	func prf30(result, secret, label, seed []byte) {
	hashSHA1 := sha1.New()
	hashMD5 := md5.New()

	done := 0
	i := 0
	// RFC 5246 section 6.3 says that the largest PRF output needed is 128
	// bytes. Since no more ciphersuites will be added to SSLv3, this will
	// remain true. Each iteration gives us 16 bytes so 10 iterations will
	// be sufficient.
	var b [11]byte
	for done < len(result) {
	for j := 0; j <= i; j++ {
	b[j] = 'A' + byte(i)
	}

	hashSHA1.Reset()
	hashSHA1.Write(b[:i+1])
	hashSHA1.Write(secret)
	hashSHA1.Write(seed)
	digest := hashSHA1.Sum(nil)

	hashMD5.Reset()
	hashMD5.Write(secret)
	hashMD5.Write(digest)

	done += copy(result[done:], hashMD5.Sum(nil))
	i++
	}
	}

	const (
	masterSecretLength = 48 // Length of a master secret in TLS 1.1.
	finishedVerifyLength = 12 // Length of verify_data in a Finished message.
	)

	var masterSecretLabel = []byte("master secret")
	var keyExpansionLabel = []byte("key expansion")
	var clientFinishedLabel = []byte("client finished")
	var serverFinishedLabel = []byte("server finished")

	func prfAndHashForVersion(version uint16, suite *cipherSuite) (func(result, secret, label, seed []byte), crypto.Hash) {
	switch version {
	case VersionSSL30:
	return prf30, crypto.Hash(0)
	case VersionTLS10, VersionTLS11:
	return prf10, crypto.Hash(0)
	case VersionTLS12:
	if suite.flags&suiteSHA384 != 0 {
	return prf12(sha512.New384), crypto.SHA384
	}
	return prf12(sha256.New), crypto.SHA256
	default:
	panic("unknown version")
	}
	}

	func prfForVersion(version uint16, suite *cipherSuite) func(result, secret, label, seed []byte) {
	prf, _ := prfAndHashForVersion(version, suite)
	return prf
	}

	// masterFromPreMasterSecret generates the master secret from the pre-master
	// secret. See RFC 5246, Section 8.1.
	func masterFromPreMasterSecret(version uint16, suite *cipherSuite, preMasterSecret, clientRandom, serverRandom []byte) []byte {
	seed := make([]byte, 0, len(clientRandom)+len(serverRandom))
	seed = append(seed, clientRandom...)
	seed = append(seed, serverRandom...)

	masterSecret := make([]byte, masterSecretLength)
	prfForVersion(version, suite)(masterSecret, preMasterSecret, masterSecretLabel, seed)
	return masterSecret
	}

	// keysFromMasterSecret generates the connection keys from the master
	// secret, given the lengths of the MAC key, cipher key and IV, as defined in
	// RFC 2246, Section 6.3.
	func keysFromMasterSecret(version uint16, suite *cipherSuite, masterSecret, clientRandom, serverRandom []byte, macLen, keyLen, ivLen int) (clientMAC, serverMAC, clientKey, serverKey, clientIV, serverIV []byte) {
	seed := make([]byte, 0, len(serverRandom)+len(clientRandom))
	seed = append(seed, serverRandom...)
	seed = append(seed, clientRandom...)

	n := 2macLen + 2keyLen + 2*ivLen
	keyMaterial := make([]byte, n)
	prfForVersion(version, suite)(keyMaterial, masterSecret, keyExpansionLabel, seed)
	clientMAC = keyMaterial[:macLen]
	keyMaterial = keyMaterial[macLen:]
	serverMAC = keyMaterial[:macLen]
	keyMaterial = keyMaterial[macLen:]
	clientKey = keyMaterial[:keyLen]
	keyMaterial = keyMaterial[keyLen:]
	serverKey = keyMaterial[:keyLen]
	keyMaterial = keyMaterial[keyLen:]
	clientIV = keyMaterial[:ivLen]
	keyMaterial = keyMaterial[ivLen:]
	serverIV = keyMaterial[:ivLen]
	return
	}

	// hashFromSignatureScheme returns the corresponding crypto.Hash for a given
	// hash from a TLS SignatureScheme.
	func hashFromSignatureScheme(signatureAlgorithm SignatureScheme) (crypto.Hash, error) {
	switch signatureAlgorithm {
	case PKCS1WithSHA1, ECDSAWithSHA1:
	return crypto.SHA1, nil
	case PKCS1WithSHA256, PSSWithSHA256, ECDSAWithP256AndSHA256:
	return crypto.SHA256, nil
	case PKCS1WithSHA384, PSSWithSHA384, ECDSAWithP384AndSHA384:
	return crypto.SHA384, nil
	case PKCS1WithSHA512, PSSWithSHA512, ECDSAWithP521AndSHA512:
	return crypto.SHA512, nil
	case Ed25519:
	return directSigning, nil
	default:
	return 0, fmt.Errorf("tls: unsupported signature algorithm: %#04x", signatureAlgorithm)
	}
	}

	func newFinishedHash(version uint16, cipherSuite *cipherSuite) finishedHash {
	var buffer []byte
	if version == VersionSSL30 \|\| version >= VersionTLS12 {
	buffer = []byte{}
	}

	prf, hash := prfAndHashForVersion(version, cipherSuite)
	if hash != 0 {
	return finishedHash{hash.New(), hash.New(), nil, nil, buffer, version, prf}
	}

	return finishedHash{sha1.New(), sha1.New(), md5.New(), md5.New(), buffer, version, prf}
	}

	// A finishedHash calculates the hash of a set of handshake messages suitable
	// for including in a Finished message.
	type finishedHash struct {
	client hash.Hash
	server hash.Hash

	// Prior to TLS 1.2, an additional MD5 hash is required.
	clientMD5 hash.Hash
	serverMD5 hash.Hash

	// In TLS 1.2, a full buffer is sadly required.
	buffer []byte

	version uint16
	prf func(result, secret, label, seed []byte)
	}

	func (h *finishedHash) Write(msg []byte) (n int, err error) {
	h.client.Write(msg)
	h.server.Write(msg)

	if h.version < VersionTLS12 {
	h.clientMD5.Write(msg)
	h.serverMD5.Write(msg)
	}

	if h.buffer != nil {
	h.buffer = append(h.buffer, msg...)
	}

	return len(msg), nil
	}

	func (h finishedHash) Sum() []byte {
	if h.version >= VersionTLS12 {
	return h.client.Sum(nil)
	}

	out := make([]byte, 0, md5.Size+sha1.Size)
	out = h.clientMD5.Sum(out)
	return h.client.Sum(out)
	}

	// finishedSum30 calculates the contents of the verify_data member of a SSLv3
	// Finished message given the MD5 and SHA1 hashes of a set of handshake
	// messages.
	func finishedSum30(md5, sha1 hash.Hash, masterSecret []byte, magic []byte) []byte {
	md5.Write(magic)
	md5.Write(masterSecret)
	md5.Write(ssl30Pad1[:])
	md5Digest := md5.Sum(nil)

	md5.Reset()
	md5.Write(masterSecret)
	md5.Write(ssl30Pad2[:])
	md5.Write(md5Digest)
	md5Digest = md5.Sum(nil)

	sha1.Write(magic)
	sha1.Write(masterSecret)
	sha1.Write(ssl30Pad1[:40])
	sha1Digest := sha1.Sum(nil)

	sha1.Reset()
	sha1.Write(masterSecret)
	sha1.Write(ssl30Pad2[:40])
	sha1.Write(sha1Digest)
	sha1Digest = sha1.Sum(nil)

	ret := make([]byte, len(md5Digest)+len(sha1Digest))
	copy(ret, md5Digest)
	copy(ret[len(md5Digest):], sha1Digest)
	return ret
	}

	var ssl3ClientFinishedMagic = [4]byte{0x43, 0x4c, 0x4e, 0x54}
	var ssl3ServerFinishedMagic = [4]byte{0x53, 0x52, 0x56, 0x52}

	// clientSum returns the contents of the verify_data member of a client's
	// Finished message.
	func (h finishedHash) clientSum(masterSecret []byte) []byte {
	if h.version == VersionSSL30 {
	return finishedSum30(h.clientMD5, h.client, masterSecret, ssl3ClientFinishedMagic[:])
	}

	out := make([]byte, finishedVerifyLength)
	h.prf(out, masterSecret, clientFinishedLabel, h.Sum())
	return out
	}

	// serverSum returns the contents of the verify_data member of a server's
	// Finished message.
	func (h finishedHash) serverSum(masterSecret []byte) []byte {
	if h.version == VersionSSL30 {
	return finishedSum30(h.serverMD5, h.server, masterSecret, ssl3ServerFinishedMagic[:])
	}

	out := make([]byte, finishedVerifyLength)
	h.prf(out, masterSecret, serverFinishedLabel, h.Sum())
	return out
	}

	// hashForClientCertificate returns the handshake messages so far, pre-hashed if
	// necessary, suitable for signing by a TLS client certificate.
	func (h finishedHash) hashForClientCertificate(sigType uint8, hashAlg crypto.Hash, masterSecret []byte) ([]byte, error) {
	if (h.version == VersionSSL30 \|\| h.version >= VersionTLS12 \|\| sigType == signatureEd25519) && h.buffer == nil {
	panic("tls: handshake hash for a client certificate requested after discarding the handshake buffer")
	}

	if h.version == VersionSSL30 {
	if sigType != signaturePKCS1v15 {
	return nil, errors.New("tls: unsupported signature type for client certificate")
	}

	md5Hash := md5.New()
	md5Hash.Write(h.buffer)
	sha1Hash := sha1.New()
	sha1Hash.Write(h.buffer)
	return finishedSum30(md5Hash, sha1Hash, masterSecret, nil), nil
	}

	if sigType == signatureEd25519 {
	return h.buffer, nil
	}

	if h.version >= VersionTLS12 {
	hash := hashAlg.New()
	hash.Write(h.buffer)
	return hash.Sum(nil), nil
	}

	if sigType == signatureECDSA {
	return h.server.Sum(nil), nil
	}

	return h.Sum(), nil
	}

	// discardHandshakeBuffer is called when there is no more need to
	// buffer the entirety of the handshake messages.
	func (h *finishedHash) discardHandshakeBuffer() {
	h.buffer = nil
	}

	// noExportedKeyingMaterial is used as a value of
	// ConnectionState.ekm when renegotation is enabled and thus
	// we wish to fail all key-material export requests.
	func noExportedKeyingMaterial(label string, context []byte, length int) ([]byte, error) {
	return nil, errors.New("crypto/tls: ExportKeyingMaterial is unavailable when renegotiation is enabled")
	}

	// ekmFromMasterSecret generates exported keying material as defined in RFC 5705.
	func ekmFromMasterSecret(version uint16, suite *cipherSuite, masterSecret, clientRandom, serverRandom []byte) func(string, []byte, int) ([]byte, error) {
	return func(label string, context []byte, length int) ([]byte, error) {
	switch label {
	case "client finished", "server finished", "master secret", "key expansion":
	// These values are reserved and may not be used.
	return nil, fmt.Errorf("crypto/tls: reserved ExportKeyingMaterial label: %s", label)
	}

	seedLen := len(serverRandom) + len(clientRandom)
	if context != nil {
	seedLen += 2 + len(context)
	}
	seed := make([]byte, 0, seedLen)

	seed = append(seed, clientRandom...)
	seed = append(seed, serverRandom...)

	if context != nil {
	if len(context) >= 1<<16 {
	return nil, fmt.Errorf("crypto/tls: ExportKeyingMaterial context too long")
	}
	seed = append(seed, byte(len(context)>>8), byte(len(context)))
	seed = append(seed, context...)
	}

	keyMaterial := make([]byte, length)
	prfForVersion(version, suite)(keyMaterial, masterSecret, []byte(label), seed)
	return keyMaterial, nil
	}
	}