/
13.go
710 lines (629 loc) · 20.6 KB
/
13.go
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package tls
import (
"bytes"
"crypto"
"crypto/ecdsa"
"crypto/elliptic"
"crypto/hmac"
"crypto/rsa"
"crypto/subtle"
"encoding/hex"
"errors"
"fmt"
"hash"
"io"
"log"
"os"
"runtime"
"runtime/debug"
"strings"
"sync/atomic"
"time"
"golang_org/x/crypto/curve25519"
)
// numSessionTickets is the number of different session tickets the
// server sends to a TLS 1.3 client, who will use each only once.
const numSessionTickets = 2
type secretLabel int
const (
secretResumptionPskBinder secretLabel = iota
secretEarlyClient
secretHandshakeClient
secretHandshakeServer
secretApplicationClient
secretApplicationServer
secretResumption
)
type keySchedule13 struct {
suite *cipherSuite
transcriptHash hash.Hash // uses the cipher suite hash algo
secret []byte // Current secret as used for Derive-Secret
handshakeCtx []byte // cached handshake context, invalidated on updates.
clientRandom []byte // Used for keylogging, nil if keylogging is disabled.
config *Config // Used for KeyLogWriter callback, nil if keylogging is disabled.
}
func newKeySchedule13(suite *cipherSuite, config *Config, clientRandom []byte) *keySchedule13 {
if config.KeyLogWriter == nil {
clientRandom = nil
config = nil
}
return &keySchedule13{
suite: suite,
transcriptHash: hashForSuite(suite).New(),
clientRandom: clientRandom,
config: config,
}
}
// setSecret sets the early/handshake/master secret based on the given secret
// (IKM). The salt is based on previous secrets (nil for the early secret).
func (ks *keySchedule13) setSecret(secret []byte) {
hash := hashForSuite(ks.suite)
salt := ks.secret
ks.secret = hkdfExtract(hash, secret, salt)
}
// write appends the data to the transcript hash context.
func (ks *keySchedule13) write(data []byte) {
ks.handshakeCtx = nil
ks.transcriptHash.Write(data)
}
func (ks *keySchedule13) getLabel(secretLabel secretLabel) (label, keylogType string) {
switch secretLabel {
case secretResumptionPskBinder:
label = "resumption psk binder key"
case secretEarlyClient:
label = "client early traffic secret"
keylogType = "CLIENT_EARLY_TRAFFIC_SECRET"
case secretHandshakeClient:
label = "client handshake traffic secret"
keylogType = "CLIENT_HANDSHAKE_TRAFFIC_SECRET"
case secretHandshakeServer:
label = "server handshake traffic secret"
keylogType = "SERVER_HANDSHAKE_TRAFFIC_SECRET"
case secretApplicationClient:
label = "client application traffic secret"
keylogType = "CLIENT_TRAFFIC_SECRET_0"
case secretApplicationServer:
label = "server application traffic secret"
keylogType = "SERVER_TRAFFIC_SECRET_0"
case secretResumption:
label = "resumption master secret"
}
return
}
// deriveSecret returns the secret derived from the handshake context and label.
func (ks *keySchedule13) deriveSecret(secretLabel secretLabel) []byte {
label, keylogType := ks.getLabel(secretLabel)
if ks.handshakeCtx == nil {
ks.handshakeCtx = ks.transcriptHash.Sum(nil)
}
hash := hashForSuite(ks.suite)
secret := hkdfExpandLabel(hash, ks.secret, ks.handshakeCtx, label, hash.Size())
if keylogType != "" && ks.config != nil {
ks.config.writeKeyLog(keylogType, ks.clientRandom, secret)
}
return secret
}
func (ks *keySchedule13) prepareCipher(secretLabel secretLabel) (interface{}, []byte) {
trafficSecret := ks.deriveSecret(secretLabel)
hash := hashForSuite(ks.suite)
key := hkdfExpandLabel(hash, trafficSecret, nil, "key", ks.suite.keyLen)
iv := hkdfExpandLabel(hash, trafficSecret, nil, "iv", 12)
return ks.suite.aead(key, iv), trafficSecret
}
func (hs *serverHandshakeState) doTLS13Handshake() error {
config := hs.c.config
c := hs.c
hs.c.cipherSuite, hs.hello13.cipherSuite = hs.suite.id, hs.suite.id
hs.c.clientHello = hs.clientHello.marshal()
// When picking the group for the handshake, priority is given to groups
// that the client provided a keyShare for, so to avoid a round-trip.
// After that the order of CurvePreferences is respected.
var ks keyShare
CurvePreferenceLoop:
for _, curveID := range config.curvePreferences() {
for _, keyShare := range hs.clientHello.keyShares {
if curveID == keyShare.group {
ks = keyShare
break CurvePreferenceLoop
}
}
}
if ks.group == 0 {
c.sendAlert(alertInternalError)
return errors.New("tls: HelloRetryRequest not implemented") // TODO(filippo)
}
if committer, ok := c.conn.(Committer); ok {
if err := committer.Commit(); err != nil {
return err
}
}
privateKey, serverKS, err := config.generateKeyShare(ks.group)
if err != nil {
c.sendAlert(alertInternalError)
return err
}
hs.hello13.keyShare = serverKS
hash := hashForSuite(hs.suite)
hashSize := hash.Size()
hs.keySchedule = newKeySchedule13(hs.suite, config, hs.clientHello.random)
// Check for PSK and update key schedule with new early secret key
isResumed, pskAlert := hs.checkPSK()
switch {
case pskAlert != alertSuccess:
c.sendAlert(pskAlert)
return errors.New("tls: invalid client PSK")
case !isResumed:
// apply an empty PSK if not resumed.
hs.keySchedule.setSecret(nil)
case isResumed:
c.didResume = true
}
hs.keySchedule.write(hs.clientHello.marshal())
earlyClientCipher, _ := hs.keySchedule.prepareCipher(secretEarlyClient)
ecdheSecret := deriveECDHESecret(ks, privateKey)
if ecdheSecret == nil {
c.sendAlert(alertIllegalParameter)
return errors.New("tls: bad ECDHE client share")
}
hs.keySchedule.write(hs.hello13.marshal())
if _, err := c.writeRecord(recordTypeHandshake, hs.hello13.marshal()); err != nil {
return err
}
hs.keySchedule.setSecret(ecdheSecret)
clientCipher, cTrafficSecret := hs.keySchedule.prepareCipher(secretHandshakeClient)
hs.hsClientCipher = clientCipher
serverCipher, sTrafficSecret := hs.keySchedule.prepareCipher(secretHandshakeServer)
c.out.setCipher(c.vers, serverCipher)
serverFinishedKey := hkdfExpandLabel(hash, sTrafficSecret, nil, "finished", hashSize)
hs.clientFinishedKey = hkdfExpandLabel(hash, cTrafficSecret, nil, "finished", hashSize)
hs.keySchedule.write(hs.hello13Enc.marshal())
if _, err := c.writeRecord(recordTypeHandshake, hs.hello13Enc.marshal()); err != nil {
return err
}
if !c.didResume {
if err := hs.sendCertificate13(); err != nil {
return err
}
}
verifyData := hmacOfSum(hash, hs.keySchedule.transcriptHash, serverFinishedKey)
serverFinished := &finishedMsg{
verifyData: verifyData,
}
hs.keySchedule.write(serverFinished.marshal())
if _, err := c.writeRecord(recordTypeHandshake, serverFinished.marshal()); err != nil {
return err
}
hs.keySchedule.setSecret(nil) // derive master secret
hs.appClientCipher, _ = hs.keySchedule.prepareCipher(secretApplicationClient)
serverCipher, _ = hs.keySchedule.prepareCipher(secretApplicationServer)
c.out.setCipher(c.vers, serverCipher)
if c.hand.Len() > 0 {
return c.sendAlert(alertUnexpectedMessage)
}
if hs.hello13Enc.earlyData {
c.in.setCipher(c.vers, earlyClientCipher)
c.phase = readingEarlyData
} else if hs.clientHello.earlyData {
c.in.setCipher(c.vers, hs.hsClientCipher)
c.phase = discardingEarlyData
} else {
c.in.setCipher(c.vers, hs.hsClientCipher)
c.phase = waitingClientFinished
}
return nil
}
// readClientFinished13 is called when, on the second flight of the client,
// a handshake message is received. This might be immediately or after the
// early data. Once done it sends the session tickets. Under c.in lock.
func (hs *serverHandshakeState) readClientFinished13() error {
c := hs.c
c.phase = readingClientFinished
msg, err := c.readHandshake()
if err != nil {
return err
}
clientFinished, ok := msg.(*finishedMsg)
if !ok {
c.sendAlert(alertUnexpectedMessage)
return unexpectedMessageError(clientFinished, msg)
}
hash := hashForSuite(hs.suite)
expectedVerifyData := hmacOfSum(hash, hs.keySchedule.transcriptHash, hs.clientFinishedKey)
if len(expectedVerifyData) != len(clientFinished.verifyData) ||
subtle.ConstantTimeCompare(expectedVerifyData, clientFinished.verifyData) != 1 {
c.sendAlert(alertDecryptError)
return errors.New("tls: client's Finished message is incorrect")
}
hs.keySchedule.write(clientFinished.marshal())
c.hs = nil // Discard the server handshake state
if c.hand.Len() > 0 {
return c.sendAlert(alertUnexpectedMessage)
}
c.in.setCipher(c.vers, hs.appClientCipher)
c.in.traceErr, c.out.traceErr = nil, nil
c.phase = handshakeConfirmed
atomic.StoreInt32(&c.handshakeConfirmed, 1)
// Any read operation after handshakeRunning and before handshakeConfirmed
// will be holding this lock, which we release as soon as the confirmation
// happens, even if the Read call might do more work.
c.confirmMutex.Unlock()
return hs.sendSessionTicket13() // TODO: do in a goroutine
}
func (hs *serverHandshakeState) sendCertificate13() error {
c := hs.c
certEntries := []certificateEntry{}
for _, cert := range hs.cert.Certificate {
certEntries = append(certEntries, certificateEntry{data: cert})
}
if len(certEntries) > 0 && hs.clientHello.ocspStapling {
certEntries[0].ocspStaple = hs.cert.OCSPStaple
}
if len(certEntries) > 0 && hs.clientHello.scts {
certEntries[0].sctList = hs.cert.SignedCertificateTimestamps
}
certMsg := &certificateMsg13{certificates: certEntries}
hs.keySchedule.write(certMsg.marshal())
if _, err := c.writeRecord(recordTypeHandshake, certMsg.marshal()); err != nil {
return err
}
sigScheme, err := hs.selectTLS13SignatureScheme()
if err != nil {
c.sendAlert(alertInternalError)
return err
}
sigHash := hashForSignatureScheme(sigScheme)
opts := crypto.SignerOpts(sigHash)
if signatureSchemeIsPSS(sigScheme) {
opts = &rsa.PSSOptions{SaltLength: rsa.PSSSaltLengthEqualsHash, Hash: sigHash}
}
toSign := prepareDigitallySigned(sigHash, "TLS 1.3, server CertificateVerify", hs.keySchedule.transcriptHash.Sum(nil))
signature, err := hs.cert.PrivateKey.(crypto.Signer).Sign(c.config.rand(), toSign[:], opts)
if err != nil {
c.sendAlert(alertInternalError)
return err
}
verifyMsg := &certificateVerifyMsg{
hasSignatureAndHash: true,
signatureAlgorithm: sigScheme,
signature: signature,
}
hs.keySchedule.write(verifyMsg.marshal())
if _, err := c.writeRecord(recordTypeHandshake, verifyMsg.marshal()); err != nil {
return err
}
return nil
}
func (c *Conn) handleEndOfEarlyData() {
if c.phase != readingEarlyData || c.vers < VersionTLS13 {
c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
return
}
c.phase = waitingClientFinished
if c.hand.Len() > 0 {
c.in.setErrorLocked(c.sendAlert(alertUnexpectedMessage))
return
}
c.in.setCipher(c.vers, c.hs.hsClientCipher)
}
// selectTLS13SignatureScheme chooses the SignatureScheme for the CertificateVerify
// based on the certificate type and client supported schemes. If no overlap is found,
// a fallback is selected.
//
// See https://tools.ietf.org/html/draft-ietf-tls-tls13-18#section-4.4.1.2
func (hs *serverHandshakeState) selectTLS13SignatureScheme() (sigScheme SignatureScheme, err error) {
var supportedSchemes []SignatureScheme
signer, ok := hs.cert.PrivateKey.(crypto.Signer)
if !ok {
return 0, errors.New("tls: certificate private key does not implement crypto.Signer")
}
pk := signer.Public()
if _, ok := pk.(*rsa.PublicKey); ok {
sigScheme = PSSWithSHA256
supportedSchemes = []SignatureScheme{PSSWithSHA256, PSSWithSHA384, PSSWithSHA512}
} else if pk, ok := pk.(*ecdsa.PublicKey); ok {
switch pk.Curve {
case elliptic.P256():
sigScheme = ECDSAWithP256AndSHA256
supportedSchemes = []SignatureScheme{ECDSAWithP256AndSHA256}
case elliptic.P384():
sigScheme = ECDSAWithP384AndSHA384
supportedSchemes = []SignatureScheme{ECDSAWithP384AndSHA384}
case elliptic.P521():
sigScheme = ECDSAWithP521AndSHA512
supportedSchemes = []SignatureScheme{ECDSAWithP521AndSHA512}
default:
return 0, errors.New("tls: unknown ECDSA certificate curve")
}
} else {
return 0, errors.New("tls: unknown certificate key type")
}
for _, ss := range supportedSchemes {
for _, cs := range hs.clientHello.supportedSignatureAlgorithms {
if ss == cs {
return ss, nil
}
}
}
return sigScheme, nil
}
func signatureSchemeIsPSS(s SignatureScheme) bool {
return s == PSSWithSHA256 || s == PSSWithSHA384 || s == PSSWithSHA512
}
// hashForSignatureScheme returns the Hash used by a SignatureScheme which is
// supported by selectTLS13SignatureScheme.
func hashForSignatureScheme(ss SignatureScheme) crypto.Hash {
switch ss {
case PSSWithSHA256, ECDSAWithP256AndSHA256:
return crypto.SHA256
case PSSWithSHA384, ECDSAWithP384AndSHA384:
return crypto.SHA384
case PSSWithSHA512, ECDSAWithP521AndSHA512:
return crypto.SHA512
default:
panic("unsupported SignatureScheme passed to hashForSignatureScheme")
}
}
func hashForSuite(suite *cipherSuite) crypto.Hash {
if suite.flags&suiteSHA384 != 0 {
return crypto.SHA384
}
return crypto.SHA256
}
func prepareDigitallySigned(hash crypto.Hash, context string, data []byte) []byte {
message := bytes.Repeat([]byte{32}, 64)
message = append(message, context...)
message = append(message, 0)
message = append(message, data...)
h := hash.New()
h.Write(message)
return h.Sum(nil)
}
func (c *Config) generateKeyShare(curveID CurveID) ([]byte, keyShare, error) {
if curveID == X25519 {
var scalar, public [32]byte
if _, err := io.ReadFull(c.rand(), scalar[:]); err != nil {
return nil, keyShare{}, err
}
curve25519.ScalarBaseMult(&public, &scalar)
return scalar[:], keyShare{group: curveID, data: public[:]}, nil
}
curve, ok := curveForCurveID(curveID)
if !ok {
return nil, keyShare{}, errors.New("tls: preferredCurves includes unsupported curve")
}
privateKey, x, y, err := elliptic.GenerateKey(curve, c.rand())
if err != nil {
return nil, keyShare{}, err
}
ecdhePublic := elliptic.Marshal(curve, x, y)
return privateKey, keyShare{group: curveID, data: ecdhePublic}, nil
}
func deriveECDHESecret(ks keyShare, secretKey []byte) []byte {
if ks.group == X25519 {
if len(ks.data) != 32 {
return nil
}
var theirPublic, sharedKey, scalar [32]byte
copy(theirPublic[:], ks.data)
copy(scalar[:], secretKey)
curve25519.ScalarMult(&sharedKey, &scalar, &theirPublic)
return sharedKey[:]
}
curve, ok := curveForCurveID(ks.group)
if !ok {
return nil
}
x, y := elliptic.Unmarshal(curve, ks.data)
if x == nil {
return nil
}
x, _ = curve.ScalarMult(x, y, secretKey)
xBytes := x.Bytes()
curveSize := (curve.Params().BitSize + 8 - 1) >> 3
if len(xBytes) == curveSize {
return xBytes
}
buf := make([]byte, curveSize)
copy(buf[len(buf)-len(xBytes):], xBytes)
return buf
}
func hkdfExpandLabel(hash crypto.Hash, secret, hashValue []byte, label string, L int) []byte {
hkdfLabel := make([]byte, 4+len("TLS 1.3, ")+len(label)+len(hashValue))
hkdfLabel[0] = byte(L >> 8)
hkdfLabel[1] = byte(L)
hkdfLabel[2] = byte(len("TLS 1.3, ") + len(label))
copy(hkdfLabel[3:], "TLS 1.3, ")
z := hkdfLabel[3+len("TLS 1.3, "):]
copy(z, label)
z = z[len(label):]
z[0] = byte(len(hashValue))
copy(z[1:], hashValue)
return hkdfExpand(hash, secret, hkdfLabel, L)
}
func hmacOfSum(f crypto.Hash, hash hash.Hash, key []byte) []byte {
h := hmac.New(f.New, key)
h.Write(hash.Sum(nil))
return h.Sum(nil)
}
// Maximum allowed mismatch between the stated age of a ticket
// and the server-observed one. See
// https://tools.ietf.org/html/draft-ietf-tls-tls13-18#section-4.2.8.2.
const ticketAgeSkewAllowance = 10 * time.Second
// checkPSK tries to resume using a PSK, returning true (and updating the
// early secret in the key schedule) if the PSK was used and false otherwise.
func (hs *serverHandshakeState) checkPSK() (isResumed bool, alert alert) {
if hs.c.config.SessionTicketsDisabled {
return false, alertSuccess
}
foundDHE := false
for _, mode := range hs.clientHello.pskKeyExchangeModes {
if mode == pskDHEKeyExchange {
foundDHE = true
break
}
}
if !foundDHE {
return false, alertSuccess
}
hash := hashForSuite(hs.suite)
hashSize := hash.Size()
for i := range hs.clientHello.psks {
sessionTicket := append([]uint8{}, hs.clientHello.psks[i].identity...)
if hs.c.config.SessionTicketSealer != nil {
var ok bool
sessionTicket, ok = hs.c.config.SessionTicketSealer.Unseal(hs.clientHelloInfo(), sessionTicket)
if !ok {
continue
}
} else {
sessionTicket, _ = hs.c.decryptTicket(sessionTicket)
if sessionTicket == nil {
continue
}
}
s := &sessionState13{}
if s.unmarshal(sessionTicket) != alertSuccess {
continue
}
if s.vers != hs.c.vers {
continue
}
clientAge := time.Duration(hs.clientHello.psks[i].obfTicketAge-s.ageAdd) * time.Millisecond
serverAge := time.Since(time.Unix(int64(s.createdAt), 0))
if clientAge-serverAge > ticketAgeSkewAllowance || clientAge-serverAge < -ticketAgeSkewAllowance {
// XXX: NSS is off spec and sends obfuscated_ticket_age as seconds
clientAge = time.Duration(hs.clientHello.psks[i].obfTicketAge-s.ageAdd) * time.Second
if clientAge-serverAge > ticketAgeSkewAllowance || clientAge-serverAge < -ticketAgeSkewAllowance {
continue
}
}
// This enforces the stricter 0-RTT requirements on all ticket uses.
// The benefit of using PSK+ECDHE without 0-RTT are small enough that
// we can give them up in the edge case of changed suite or ALPN or SNI.
if s.suite != hs.suite.id {
continue
}
if s.alpnProtocol != hs.c.clientProtocol {
continue
}
if s.SNI != hs.c.serverName {
continue
}
hs.keySchedule.setSecret(s.resumptionSecret)
binderKey := hs.keySchedule.deriveSecret(secretResumptionPskBinder)
binderFinishedKey := hkdfExpandLabel(hash, binderKey, nil, "finished", hashSize)
chHash := hash.New()
chHash.Write(hs.clientHello.rawTruncated)
expectedBinder := hmacOfSum(hash, chHash, binderFinishedKey)
if subtle.ConstantTimeCompare(expectedBinder, hs.clientHello.psks[i].binder) != 1 {
return false, alertDecryptError
}
if i == 0 && hs.clientHello.earlyData {
// This is a ticket intended to be used for 0-RTT
if s.maxEarlyDataLen == 0 {
// But we had not tagged it as such.
return false, alertIllegalParameter
}
if hs.c.config.Accept0RTTData {
hs.c.binder = expectedBinder
hs.c.ticketMaxEarlyData = int64(s.maxEarlyDataLen)
hs.hello13Enc.earlyData = true
}
}
hs.hello13.psk = true
hs.hello13.pskIdentity = uint16(i)
return true, alertSuccess
}
return false, alertSuccess
}
func (hs *serverHandshakeState) sendSessionTicket13() error {
c := hs.c
if c.config.SessionTicketsDisabled {
return nil
}
foundDHE := false
for _, mode := range hs.clientHello.pskKeyExchangeModes {
if mode == pskDHEKeyExchange {
foundDHE = true
break
}
}
if !foundDHE {
return nil
}
resumptionSecret := hs.keySchedule.deriveSecret(secretResumption)
ageAddBuf := make([]byte, 4)
sessionState := &sessionState13{
vers: c.vers,
suite: hs.suite.id,
createdAt: uint64(time.Now().Unix()),
resumptionSecret: resumptionSecret,
alpnProtocol: c.clientProtocol,
SNI: c.serverName,
maxEarlyDataLen: c.config.Max0RTTDataSize,
}
for i := 0; i < numSessionTickets; i++ {
if _, err := io.ReadFull(c.config.rand(), ageAddBuf); err != nil {
c.sendAlert(alertInternalError)
return err
}
sessionState.ageAdd = uint32(ageAddBuf[0])<<24 | uint32(ageAddBuf[1])<<16 |
uint32(ageAddBuf[2])<<8 | uint32(ageAddBuf[3])
ticket := sessionState.marshal()
var err error
if c.config.SessionTicketSealer != nil {
cs := c.ConnectionState()
ticket, err = c.config.SessionTicketSealer.Seal(&cs, ticket)
} else {
ticket, err = c.encryptTicket(ticket)
}
if err != nil {
c.sendAlert(alertInternalError)
return err
}
if ticket == nil {
continue
}
ticketMsg := &newSessionTicketMsg13{
lifetime: 24 * 3600, // TODO(filippo)
maxEarlyDataLength: c.config.Max0RTTDataSize,
withEarlyDataInfo: c.config.Max0RTTDataSize > 0,
ageAdd: sessionState.ageAdd,
ticket: ticket,
}
if _, err := c.writeRecord(recordTypeHandshake, ticketMsg.marshal()); err != nil {
return err
}
}
return nil
}
func (hs *serverHandshakeState) traceErr(err error) {
if err == nil {
return
}
if os.Getenv("TLSDEBUG") == "error" {
if hs != nil && hs.clientHello != nil {
os.Stderr.WriteString(hex.Dump(hs.clientHello.marshal()))
} else if err == io.EOF {
return // don't stack trace on EOF before CH
}
fmt.Fprintf(os.Stderr, "\n%s\n", debug.Stack())
}
if os.Getenv("TLSDEBUG") == "short" {
var pcs [4]uintptr
frames := runtime.CallersFrames(pcs[0:runtime.Callers(3, pcs[:])])
for {
frame, more := frames.Next()
if frame.Function != "crypto/tls.(*halfConn).setErrorLocked" &&
frame.Function != "crypto/tls.(*Conn).sendAlertLocked" &&
frame.Function != "crypto/tls.(*Conn).sendAlert" {
file := frame.File[strings.LastIndex(frame.File, "/")+1:]
log.Printf("%s:%d (%s): %v", file, frame.Line, frame.Function, err)
return
}
if !more {
break
}
}
}
}