ssl/test/runner/prf.go - boringssl - 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 runner

 import (
 	"crypto"
 	"crypto/hmac"
 	"crypto/md5"
 	"crypto/sha1"
 	"crypto/sha256"
 	"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)
 		todo := len(b)
 		if j+todo > len(result) {
 			todo = len(result) - j
 		}
 		copy(result[j:j+todo], b)
 		j += todo

 		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
 	// RFC5246 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 (
 	tlsRandomLength      = 32 // Length of a random nonce in TLS 1.1.
 	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 extendedMasterSecretLabel = []byte("extended master secret")
 var keyExpansionLabel = []byte("key expansion")
 var clientFinishedLabel = []byte("client finished")
 var serverFinishedLabel = []byte("server finished")
 var finishedLabel = []byte("finished")
 var channelIDLabel = []byte("TLS Channel ID signature\x00")
 var channelIDResumeLabel = []byte("Resumption\x00")

 func prfForVersion(version uint16, suite *cipherSuite) func(result, secret, label, seed []byte) {
 	switch version {
 	case VersionSSL30:
 		return prf30
 	case VersionTLS10, VersionTLS11:
 		return prf10
 	case VersionTLS12:
 		return prf12(suite.hash().New)
 	}
 	panic("unknown version")
 }

 // masterFromPreMasterSecret generates the master secret from the pre-master
 // secret. See http://tools.ietf.org/html/rfc5246#section-8.1
 func masterFromPreMasterSecret(version uint16, suite *cipherSuite, preMasterSecret, clientRandom, serverRandom []byte) []byte {
 	var seed [tlsRandomLength * 2]byte
 	copy(seed[0:len(clientRandom)], clientRandom)
 	copy(seed[len(clientRandom):], serverRandom)
 	masterSecret := make([]byte, masterSecretLength)
 	prfForVersion(version, suite)(masterSecret, preMasterSecret, masterSecretLabel, seed[0:])
 	return masterSecret
 }

 // extendedMasterFromPreMasterSecret generates the master secret from the
 // pre-master secret when the Triple Handshake fix is in effect. See
 // https://tools.ietf.org/html/rfc7627
 func extendedMasterFromPreMasterSecret(version uint16, suite *cipherSuite, preMasterSecret []byte, h finishedHash) []byte {
 	masterSecret := make([]byte, masterSecretLength)
 	prfForVersion(version, suite)(masterSecret, preMasterSecret, extendedMasterSecretLabel, h.Sum())
 	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) {
 	var seed [tlsRandomLength * 2]byte
 	copy(seed[0:len(clientRandom)], serverRandom)
 	copy(seed[len(serverRandom):], clientRandom)

 	n := 2*macLen + 2*keyLen + 2*ivLen
 	keyMaterial := make([]byte, n)
 	prfForVersion(version, suite)(keyMaterial, masterSecret, keyExpansionLabel, seed[0:])
 	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
 }

 func newFinishedHash(version uint16, cipherSuite *cipherSuite) finishedHash {
 	var ret finishedHash

 	if version >= VersionTLS12 {
 		ret.hash = cipherSuite.hash()

 		ret.client = ret.hash.New()
 		ret.server = ret.hash.New()

 		if version == VersionTLS12 {
 			ret.prf = prf12(ret.hash.New)
 		} else {
 			ret.secret = make([]byte, ret.hash.Size())
 		}
 	} else {
 		ret.hash = crypto.MD5SHA1

 		ret.client = sha1.New()
 		ret.server = sha1.New()
 		ret.clientMD5 = md5.New()
 		ret.serverMD5 = md5.New()

 		ret.prf = prf10
 	}

 	ret.buffer = []byte{}
 	ret.version = version
 	return ret
 }

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

 	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 (and SSL 3 for implementation convenience), a
 	// full buffer is required.
 	buffer []byte

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

 	// secret, in TLS 1.3, is the running input secret.
 	secret []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(baseKey []byte) []byte {
 	if h.version == VersionSSL30 {
 		return finishedSum30(h.clientMD5, h.client, baseKey, ssl3ClientFinishedMagic[:])
 	}

 	if h.version < VersionTLS13 {
 		out := make([]byte, finishedVerifyLength)
 		h.prf(out, baseKey, clientFinishedLabel, h.Sum())
 		return out
 	}

 	clientFinishedKey := hkdfExpandLabel(h.hash, baseKey, finishedLabel, nil, h.hash.Size())
 	finishedHMAC := hmac.New(h.hash.New, clientFinishedKey)
 	finishedHMAC.Write(h.appendContextHashes(nil))
 	return finishedHMAC.Sum(nil)
 }

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

 	if h.version < VersionTLS13 {
 		out := make([]byte, finishedVerifyLength)
 		h.prf(out, baseKey, serverFinishedLabel, h.Sum())
 		return out
 	}

 	serverFinishedKey := hkdfExpandLabel(h.hash, baseKey, finishedLabel, nil, h.hash.Size())
 	finishedHMAC := hmac.New(h.hash.New, serverFinishedKey)
 	finishedHMAC.Write(h.appendContextHashes(nil))
 	return finishedHMAC.Sum(nil)
 }

 // hashForClientCertificateSSL3 returns the hash to be signed for client
 // certificates in SSL 3.0.
 func (h finishedHash) hashForClientCertificateSSL3(masterSecret []byte) []byte {
 	md5Hash := md5.New()
 	md5Hash.Write(h.buffer)
 	sha1Hash := sha1.New()
 	sha1Hash.Write(h.buffer)
 	return finishedSum30(md5Hash, sha1Hash, masterSecret, nil)
 }

 // hashForChannelID returns the hash to be signed for TLS Channel
 // ID. If a resumption, resumeHash has the previous handshake
 // hash. Otherwise, it is nil.
 func (h finishedHash) hashForChannelID(resumeHash []byte) []byte {
 	hash := sha256.New()
 	hash.Write(channelIDLabel)
 	if resumeHash != nil {
 		hash.Write(channelIDResumeLabel)
 		hash.Write(resumeHash)
 	}
 	hash.Write(h.Sum())
 	return hash.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
 }

 // zeroSecretTLS13 returns the default all zeros secret for TLS 1.3, used when a
 // given secret is not available in the handshake. See draft-ietf-tls-tls13-16,
 // section 7.1.
 func (h *finishedHash) zeroSecret() []byte {
 	return make([]byte, h.hash.Size())
 }

 // addEntropy incorporates ikm into the running TLS 1.3 secret with HKDF-Expand.
 func (h *finishedHash) addEntropy(ikm []byte) {
 	h.secret = hkdfExtract(h.hash.New, h.secret, ikm)
 }

 // hkdfExpandLabel implements TLS 1.3's HKDF-Expand-Label function, as defined
 // in section 7.1 of draft-ietf-tls-tls13-16.
 func hkdfExpandLabel(hash crypto.Hash, secret, label, hashValue []byte, length int) []byte {
 	if len(label) > 255 || len(hashValue) > 255 {
 		panic("hkdfExpandLabel: label or hashValue too long")
 	}
 	hkdfLabel := make([]byte, 3+9+len(label)+1+len(hashValue))
 	x := hkdfLabel
 	x[0] = byte(length >> 8)
 	x[1] = byte(length)
 	x[2] = byte(9 + len(label))
 	x = x[3:]
 	copy(x, []byte("TLS 1.3, "))
 	x = x[9:]
 	copy(x, label)
 	x = x[len(label):]
 	x[0] = byte(len(hashValue))
 	copy(x[1:], hashValue)
 	return hkdfExpand(hash.New, secret, hkdfLabel, length)
 }

 // appendContextHashes returns the concatenation of the handshake hash and the
 // resumption context hash, as used in TLS 1.3.
 func (h *finishedHash) appendContextHashes(b []byte) []byte {
 	b = h.client.Sum(b)
 	return b
 }

 // The following are labels for traffic secret derivation in TLS 1.3.
 var (
 	externalPSKBinderLabel        = []byte("external psk binder key")
 	resumptionPSKBinderLabel      = []byte("resumption psk binder key")
 	earlyTrafficLabel             = []byte("client early traffic secret")
 	clientHandshakeTrafficLabel   = []byte("client handshake traffic secret")
 	serverHandshakeTrafficLabel   = []byte("server handshake traffic secret")
 	clientApplicationTrafficLabel = []byte("client application traffic secret")
 	serverApplicationTrafficLabel = []byte("server application traffic secret")
 	applicationTrafficLabel       = []byte("application traffic secret")
 	exporterLabel                 = []byte("exporter master secret")
 	resumptionLabel               = []byte("resumption master secret")
 )

 // deriveSecret implements TLS 1.3's Derive-Secret function, as defined in
 // section 7.1 of draft ietf-tls-tls13-16.
 func (h *finishedHash) deriveSecret(label []byte) []byte {
 	return hkdfExpandLabel(h.hash, h.secret, label, h.appendContextHashes(nil), h.hash.Size())
 }

 // The following are context strings for CertificateVerify in TLS 1.3.
 var (
 	clientCertificateVerifyContextTLS13 = []byte("TLS 1.3, client CertificateVerify")
 	serverCertificateVerifyContextTLS13 = []byte("TLS 1.3, server CertificateVerify")
 	channelIDContextTLS13               = []byte("TLS 1.3, Channel ID")
 )

 // certificateVerifyMessage returns the input to be signed for CertificateVerify
 // in TLS 1.3.
 func (h *finishedHash) certificateVerifyInput(context []byte) []byte {
 	const paddingLen = 64
 	b := make([]byte, paddingLen, paddingLen+len(context)+1+2*h.hash.Size())
 	for i := 0; i < paddingLen; i++ {
 		b[i] = 32
 	}
 	b = append(b, context...)
 	b = append(b, 0)
 	b = h.appendContextHashes(b)
 	return b
 }

 type trafficDirection int

 const (
 	clientWrite trafficDirection = iota
 	serverWrite
 )

 var (
 	keyTLS13 = []byte("key")
 	ivTLS13  = []byte("iv")
 )

 // deriveTrafficAEAD derives traffic keys and constructs an AEAD given a traffic
 // secret.
 func deriveTrafficAEAD(version uint16, suite *cipherSuite, secret []byte, side trafficDirection) interface{} {
 	key := hkdfExpandLabel(suite.hash(), secret, keyTLS13, nil, suite.keyLen)
 	iv := hkdfExpandLabel(suite.hash(), secret, ivTLS13, nil, suite.ivLen(version))

 	return suite.aead(version, key, iv)
 }

 func updateTrafficSecret(hash crypto.Hash, secret []byte) []byte {
 	return hkdfExpandLabel(hash, secret, applicationTrafficLabel, nil, hash.Size())
 }

 func computePSKBinder(psk, label []byte, cipherSuite *cipherSuite, transcript, truncatedHello []byte) []byte {
 	finishedHash := newFinishedHash(VersionTLS13, cipherSuite)
 	finishedHash.addEntropy(psk)
 	binderKey := finishedHash.deriveSecret(label)
 	finishedHash.Write(transcript)
 	finishedHash.Write(truncatedHello)
 	return finishedHash.clientSum(binderKey)
 }
	// 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 runner

	import (
	"crypto"
	"crypto/hmac"
	"crypto/md5"
	"crypto/sha1"
	"crypto/sha256"
	"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)
	todo := len(b)
	if j+todo > len(result) {
	todo = len(result) - j
	}
	copy(result[j:j+todo], b)
	j += todo

	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
	// RFC5246 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 (
	tlsRandomLength = 32 // Length of a random nonce in TLS 1.1.
	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 extendedMasterSecretLabel = []byte("extended master secret")
	var keyExpansionLabel = []byte("key expansion")
	var clientFinishedLabel = []byte("client finished")
	var serverFinishedLabel = []byte("server finished")
	var finishedLabel = []byte("finished")
	var channelIDLabel = []byte("TLS Channel ID signature\x00")
	var channelIDResumeLabel = []byte("Resumption\x00")

	func prfForVersion(version uint16, suite *cipherSuite) func(result, secret, label, seed []byte) {
	switch version {
	case VersionSSL30:
	return prf30
	case VersionTLS10, VersionTLS11:
	return prf10
	case VersionTLS12:
	return prf12(suite.hash().New)
	}
	panic("unknown version")
	}

	// masterFromPreMasterSecret generates the master secret from the pre-master
	// secret. See http://tools.ietf.org/html/rfc5246#section-8.1
	func masterFromPreMasterSecret(version uint16, suite *cipherSuite, preMasterSecret, clientRandom, serverRandom []byte) []byte {
	var seed [tlsRandomLength * 2]byte
	copy(seed[0:len(clientRandom)], clientRandom)
	copy(seed[len(clientRandom):], serverRandom)
	masterSecret := make([]byte, masterSecretLength)
	prfForVersion(version, suite)(masterSecret, preMasterSecret, masterSecretLabel, seed[0:])
	return masterSecret
	}

	// extendedMasterFromPreMasterSecret generates the master secret from the
	// pre-master secret when the Triple Handshake fix is in effect. See
	// https://tools.ietf.org/html/rfc7627
	func extendedMasterFromPreMasterSecret(version uint16, suite *cipherSuite, preMasterSecret []byte, h finishedHash) []byte {
	masterSecret := make([]byte, masterSecretLength)
	prfForVersion(version, suite)(masterSecret, preMasterSecret, extendedMasterSecretLabel, h.Sum())
	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) {
	var seed [tlsRandomLength * 2]byte
	copy(seed[0:len(clientRandom)], serverRandom)
	copy(seed[len(serverRandom):], clientRandom)

	n := 2macLen + 2keyLen + 2*ivLen
	keyMaterial := make([]byte, n)
	prfForVersion(version, suite)(keyMaterial, masterSecret, keyExpansionLabel, seed[0:])
	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
	}

	func newFinishedHash(version uint16, cipherSuite *cipherSuite) finishedHash {
	var ret finishedHash

	if version >= VersionTLS12 {
	ret.hash = cipherSuite.hash()

	ret.client = ret.hash.New()
	ret.server = ret.hash.New()

	if version == VersionTLS12 {
	ret.prf = prf12(ret.hash.New)
	} else {
	ret.secret = make([]byte, ret.hash.Size())
	}
	} else {
	ret.hash = crypto.MD5SHA1

	ret.client = sha1.New()
	ret.server = sha1.New()
	ret.clientMD5 = md5.New()
	ret.serverMD5 = md5.New()

	ret.prf = prf10
	}

	ret.buffer = []byte{}
	ret.version = version
	return ret
	}

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

	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 (and SSL 3 for implementation convenience), a
	// full buffer is required.
	buffer []byte

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

	// secret, in TLS 1.3, is the running input secret.
	secret []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(baseKey []byte) []byte {
	if h.version == VersionSSL30 {
	return finishedSum30(h.clientMD5, h.client, baseKey, ssl3ClientFinishedMagic[:])
	}

	if h.version < VersionTLS13 {
	out := make([]byte, finishedVerifyLength)
	h.prf(out, baseKey, clientFinishedLabel, h.Sum())
	return out
	}

	clientFinishedKey := hkdfExpandLabel(h.hash, baseKey, finishedLabel, nil, h.hash.Size())
	finishedHMAC := hmac.New(h.hash.New, clientFinishedKey)
	finishedHMAC.Write(h.appendContextHashes(nil))
	return finishedHMAC.Sum(nil)
	}

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

	if h.version < VersionTLS13 {
	out := make([]byte, finishedVerifyLength)
	h.prf(out, baseKey, serverFinishedLabel, h.Sum())
	return out
	}

	serverFinishedKey := hkdfExpandLabel(h.hash, baseKey, finishedLabel, nil, h.hash.Size())
	finishedHMAC := hmac.New(h.hash.New, serverFinishedKey)
	finishedHMAC.Write(h.appendContextHashes(nil))
	return finishedHMAC.Sum(nil)
	}

	// hashForClientCertificateSSL3 returns the hash to be signed for client
	// certificates in SSL 3.0.
	func (h finishedHash) hashForClientCertificateSSL3(masterSecret []byte) []byte {
	md5Hash := md5.New()
	md5Hash.Write(h.buffer)
	sha1Hash := sha1.New()
	sha1Hash.Write(h.buffer)
	return finishedSum30(md5Hash, sha1Hash, masterSecret, nil)
	}

	// hashForChannelID returns the hash to be signed for TLS Channel
	// ID. If a resumption, resumeHash has the previous handshake
	// hash. Otherwise, it is nil.
	func (h finishedHash) hashForChannelID(resumeHash []byte) []byte {
	hash := sha256.New()
	hash.Write(channelIDLabel)
	if resumeHash != nil {
	hash.Write(channelIDResumeLabel)
	hash.Write(resumeHash)
	}
	hash.Write(h.Sum())
	return hash.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
	}

	// zeroSecretTLS13 returns the default all zeros secret for TLS 1.3, used when a
	// given secret is not available in the handshake. See draft-ietf-tls-tls13-16,
	// section 7.1.
	func (h *finishedHash) zeroSecret() []byte {
	return make([]byte, h.hash.Size())
	}

	// addEntropy incorporates ikm into the running TLS 1.3 secret with HKDF-Expand.
	func (h *finishedHash) addEntropy(ikm []byte) {
	h.secret = hkdfExtract(h.hash.New, h.secret, ikm)
	}

	// hkdfExpandLabel implements TLS 1.3's HKDF-Expand-Label function, as defined
	// in section 7.1 of draft-ietf-tls-tls13-16.
	func hkdfExpandLabel(hash crypto.Hash, secret, label, hashValue []byte, length int) []byte {
	if len(label) > 255 \|\| len(hashValue) > 255 {
	panic("hkdfExpandLabel: label or hashValue too long")
	}
	hkdfLabel := make([]byte, 3+9+len(label)+1+len(hashValue))
	x := hkdfLabel
	x[0] = byte(length >> 8)
	x[1] = byte(length)
	x[2] = byte(9 + len(label))
	x = x[3:]
	copy(x, []byte("TLS 1.3, "))
	x = x[9:]
	copy(x, label)
	x = x[len(label):]
	x[0] = byte(len(hashValue))
	copy(x[1:], hashValue)
	return hkdfExpand(hash.New, secret, hkdfLabel, length)
	}

	// appendContextHashes returns the concatenation of the handshake hash and the
	// resumption context hash, as used in TLS 1.3.
	func (h *finishedHash) appendContextHashes(b []byte) []byte {
	b = h.client.Sum(b)
	return b
	}

	// The following are labels for traffic secret derivation in TLS 1.3.
	var (
	externalPSKBinderLabel = []byte("external psk binder key")
	resumptionPSKBinderLabel = []byte("resumption psk binder key")
	earlyTrafficLabel = []byte("client early traffic secret")
	clientHandshakeTrafficLabel = []byte("client handshake traffic secret")
	serverHandshakeTrafficLabel = []byte("server handshake traffic secret")
	clientApplicationTrafficLabel = []byte("client application traffic secret")
	serverApplicationTrafficLabel = []byte("server application traffic secret")
	applicationTrafficLabel = []byte("application traffic secret")
	exporterLabel = []byte("exporter master secret")
	resumptionLabel = []byte("resumption master secret")
	)

	// deriveSecret implements TLS 1.3's Derive-Secret function, as defined in
	// section 7.1 of draft ietf-tls-tls13-16.
	func (h *finishedHash) deriveSecret(label []byte) []byte {
	return hkdfExpandLabel(h.hash, h.secret, label, h.appendContextHashes(nil), h.hash.Size())
	}

	// The following are context strings for CertificateVerify in TLS 1.3.
	var (
	clientCertificateVerifyContextTLS13 = []byte("TLS 1.3, client CertificateVerify")
	serverCertificateVerifyContextTLS13 = []byte("TLS 1.3, server CertificateVerify")
	channelIDContextTLS13 = []byte("TLS 1.3, Channel ID")
	)

	// certificateVerifyMessage returns the input to be signed for CertificateVerify
	// in TLS 1.3.
	func (h *finishedHash) certificateVerifyInput(context []byte) []byte {
	const paddingLen = 64
	b := make([]byte, paddingLen, paddingLen+len(context)+1+2*h.hash.Size())
	for i := 0; i < paddingLen; i++ {
	b[i] = 32
	}
	b = append(b, context...)
	b = append(b, 0)
	b = h.appendContextHashes(b)
	return b
	}

	type trafficDirection int

	const (
	clientWrite trafficDirection = iota
	serverWrite
	)

	var (
	keyTLS13 = []byte("key")
	ivTLS13 = []byte("iv")
	)

	// deriveTrafficAEAD derives traffic keys and constructs an AEAD given a traffic
	// secret.
	func deriveTrafficAEAD(version uint16, suite *cipherSuite, secret []byte, side trafficDirection) interface{} {
	key := hkdfExpandLabel(suite.hash(), secret, keyTLS13, nil, suite.keyLen)
	iv := hkdfExpandLabel(suite.hash(), secret, ivTLS13, nil, suite.ivLen(version))

	return suite.aead(version, key, iv)
	}

	func updateTrafficSecret(hash crypto.Hash, secret []byte) []byte {
	return hkdfExpandLabel(hash, secret, applicationTrafficLabel, nil, hash.Size())
	}

	func computePSKBinder(psk, label []byte, cipherSuite *cipherSuite, transcript, truncatedHello []byte) []byte {
	finishedHash := newFinishedHash(VersionTLS13, cipherSuite)
	finishedHash.addEntropy(psk)
	binderKey := finishedHash.deriveSecret(label)
	finishedHash.Write(transcript)
	finishedHash.Write(truncatedHello)
	return finishedHash.clientSum(binderKey)
	}