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// Copyright 2010 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.
// TLS low level connection and record layer
package tls
import (
"bytes"
"crypto/cipher"
"crypto/subtle"
"crypto/x509"
"hash"
"io"
"net"
"os"
"sync"
)
// A Conn represents a secured connection.
// It implements the net.Conn interface.
type Conn struct {
// constant
conn net.Conn
isClient bool
// constant after handshake; protected by handshakeMutex
handshakeMutex sync.Mutex // handshakeMutex < in.Mutex, out.Mutex, errMutex
vers uint16 // TLS version
haveVers bool // version has been negotiated
config *Config // configuration passed to constructor
handshakeComplete bool
cipherSuite uint16
ocspResponse []byte // stapled OCSP response
peerCertificates []*x509.Certificate
clientProtocol string
// first permanent error
errMutex sync.Mutex
err os.Error
// input/output
in, out halfConn // in.Mutex < out.Mutex
rawInput *block // raw input, right off the wire
input *block // application data waiting to be read
hand bytes.Buffer // handshake data waiting to be read
tmp [16]byte
}
func (c *Conn) setError(err os.Error) os.Error {
c.errMutex.Lock()
defer c.errMutex.Unlock()
if c.err == nil {
c.err = err
}
return err
}
func (c *Conn) error() os.Error {
c.errMutex.Lock()
defer c.errMutex.Unlock()
return c.err
}
// Access to net.Conn methods.
// Cannot just embed net.Conn because that would
// export the struct field too.
// LocalAddr returns the local network address.
func (c *Conn) LocalAddr() net.Addr {
return c.conn.LocalAddr()
}
// RemoteAddr returns the remote network address.
func (c *Conn) RemoteAddr() net.Addr {
return c.conn.RemoteAddr()
}
// SetTimeout sets the read deadline associated with the connection.
// There is no write deadline.
func (c *Conn) SetTimeout(nsec int64) os.Error {
return c.conn.SetTimeout(nsec)
}
// SetReadTimeout sets the time (in nanoseconds) that
// Read will wait for data before returning os.EAGAIN.
// Setting nsec == 0 (the default) disables the deadline.
func (c *Conn) SetReadTimeout(nsec int64) os.Error {
return c.conn.SetReadTimeout(nsec)
}
// SetWriteTimeout exists to satisfy the net.Conn interface
// but is not implemented by TLS. It always returns an error.
func (c *Conn) SetWriteTimeout(nsec int64) os.Error {
return os.NewError("TLS does not support SetWriteTimeout")
}
// A halfConn represents one direction of the record layer
// connection, either sending or receiving.
type halfConn struct {
sync.Mutex
cipher interface{} // cipher algorithm
mac hash.Hash // MAC algorithm
seq [8]byte // 64-bit sequence number
bfree *block // list of free blocks
nextCipher interface{} // next encryption state
nextMac hash.Hash // next MAC algorithm
}
// prepareCipherSpec sets the encryption and MAC states
// that a subsequent changeCipherSpec will use.
func (hc *halfConn) prepareCipherSpec(cipher interface{}, mac hash.Hash) {
hc.nextCipher = cipher
hc.nextMac = mac
}
// changeCipherSpec changes the encryption and MAC states
// to the ones previously passed to prepareCipherSpec.
func (hc *halfConn) changeCipherSpec() os.Error {
if hc.nextCipher == nil {
return alertInternalError
}
hc.cipher = hc.nextCipher
hc.mac = hc.nextMac
hc.nextCipher = nil
hc.nextMac = nil
return nil
}
// incSeq increments the sequence number.
func (hc *halfConn) incSeq() {
for i := 7; i >= 0; i-- {
hc.seq[i]++
if hc.seq[i] != 0 {
return
}
}
// Not allowed to let sequence number wrap.
// Instead, must renegotiate before it does.
// Not likely enough to bother.
panic("TLS: sequence number wraparound")
}
// resetSeq resets the sequence number to zero.
func (hc *halfConn) resetSeq() {
for i := range hc.seq {
hc.seq[i] = 0
}
}
// removePadding returns an unpadded slice, in constant time, which is a prefix
// of the input. It also returns a byte which is equal to 255 if the padding
// was valid and 0 otherwise. See RFC 2246, section 6.2.3.2
func removePadding(payload []byte) ([]byte, byte) {
if len(payload) < 1 {
return payload, 0
}
paddingLen := payload[len(payload)-1]
t := uint(len(payload)-1) - uint(paddingLen)
// if len(payload) >= (paddingLen - 1) then the MSB of t is zero
good := byte(int32(^t) >> 31)
toCheck := 255 // the maximum possible padding length
// The length of the padded data is public, so we can use an if here
if toCheck+1 > len(payload) {
toCheck = len(payload) - 1
}
for i := 0; i < toCheck; i++ {
t := uint(paddingLen) - uint(i)
// if i <= paddingLen then the MSB of t is zero
mask := byte(int32(^t) >> 31)
b := payload[len(payload)-1-i]
good &^= mask&paddingLen ^ mask&b
}
// We AND together the bits of good and replicate the result across
// all the bits.
good &= good << 4
good &= good << 2
good &= good << 1
good = uint8(int8(good) >> 7)
toRemove := good&paddingLen + 1
return payload[:len(payload)-int(toRemove)], good
}
func roundUp(a, b int) int {
return a + (b-a%b)%b
}
// decrypt checks and strips the mac and decrypts the data in b.
func (hc *halfConn) decrypt(b *block) (bool, alert) {
// pull out payload
payload := b.data[recordHeaderLen:]
macSize := 0
if hc.mac != nil {
macSize = hc.mac.Size()
}
paddingGood := byte(255)
// decrypt
if hc.cipher != nil {
switch c := hc.cipher.(type) {
case cipher.Stream:
c.XORKeyStream(payload, payload)
case cipher.BlockMode:
blockSize := c.BlockSize()
if len(payload)%blockSize != 0 || len(payload) < roundUp(macSize+1, blockSize) {
return false, alertBadRecordMAC
}
c.CryptBlocks(payload, payload)
payload, paddingGood = removePadding(payload)
b.resize(recordHeaderLen + len(payload))
// note that we still have a timing side-channel in the
// MAC check, below. An attacker can align the record
// so that a correct padding will cause one less hash
// block to be calculated. Then they can iteratively
// decrypt a record by breaking each byte. See
// "Password Interception in a SSL/TLS Channel", Brice
// Canvel et al.
//
// However, our behaviour matches OpenSSL, so we leak
// only as much as they do.
default:
panic("unknown cipher type")
}
}
// check, strip mac
if hc.mac != nil {
if len(payload) < macSize {
return false, alertBadRecordMAC
}
// strip mac off payload, b.data
n := len(payload) - macSize
b.data[3] = byte(n >> 8)
b.data[4] = byte(n)
b.resize(recordHeaderLen + n)
remoteMAC := payload[n:]
hc.mac.Reset()
hc.mac.Write(hc.seq[0:])
hc.incSeq()
hc.mac.Write(b.data)
if subtle.ConstantTimeCompare(hc.mac.Sum(), remoteMAC) != 1 || paddingGood != 255 {
return false, alertBadRecordMAC
}
}
return true, 0
}
// padToBlockSize calculates the needed padding block, if any, for a payload.
// On exit, prefix aliases payload and extends to the end of the last full
// block of payload. finalBlock is a fresh slice which contains the contents of
// any suffix of payload as well as the needed padding to make finalBlock a
// full block.
func padToBlockSize(payload []byte, blockSize int) (prefix, finalBlock []byte) {
overrun := len(payload) % blockSize
paddingLen := blockSize - overrun
prefix = payload[:len(payload)-overrun]
finalBlock = make([]byte, blockSize)
copy(finalBlock, payload[len(payload)-overrun:])
for i := overrun; i < blockSize; i++ {
finalBlock[i] = byte(paddingLen - 1)
}
return
}
// encrypt encrypts and macs the data in b.
func (hc *halfConn) encrypt(b *block) (bool, alert) {
// mac
if hc.mac != nil {
hc.mac.Reset()
hc.mac.Write(hc.seq[0:])
hc.incSeq()
hc.mac.Write(b.data)
mac := hc.mac.Sum()
n := len(b.data)
b.resize(n + len(mac))
copy(b.data[n:], mac)
}
payload := b.data[recordHeaderLen:]
// encrypt
if hc.cipher != nil {
switch c := hc.cipher.(type) {
case cipher.Stream:
c.XORKeyStream(payload, payload)
case cipher.BlockMode:
prefix, finalBlock := padToBlockSize(payload, c.BlockSize())
b.resize(recordHeaderLen + len(prefix) + len(finalBlock))
c.CryptBlocks(b.data[recordHeaderLen:], prefix)
c.CryptBlocks(b.data[recordHeaderLen+len(prefix):], finalBlock)
default:
panic("unknown cipher type")
}
}
// update length to include MAC and any block padding needed.
n := len(b.data) - recordHeaderLen
b.data[3] = byte(n >> 8)
b.data[4] = byte(n)
return true, 0
}
// A block is a simple data buffer.
type block struct {
data []byte
off int // index for Read
link *block
}
// resize resizes block to be n bytes, growing if necessary.
func (b *block) resize(n int) {
if n > cap(b.data) {
b.reserve(n)
}
b.data = b.data[0:n]
}
// reserve makes sure that block contains a capacity of at least n bytes.
func (b *block) reserve(n int) {
if cap(b.data) >= n {
return
}
m := cap(b.data)
if m == 0 {
m = 1024
}
for m < n {
m *= 2
}
data := make([]byte, len(b.data), m)
copy(data, b.data)
b.data = data
}
// readFromUntil reads from r into b until b contains at least n bytes
// or else returns an error.
func (b *block) readFromUntil(r io.Reader, n int) os.Error {
// quick case
if len(b.data) >= n {
return nil
}
// read until have enough.
b.reserve(n)
for {
m, err := r.Read(b.data[len(b.data):cap(b.data)])
b.data = b.data[0 : len(b.data)+m]
if len(b.data) >= n {
break
}
if err != nil {
return err
}
}
return nil
}
func (b *block) Read(p []byte) (n int, err os.Error) {
n = copy(p, b.data[b.off:])
b.off += n
return
}
// newBlock allocates a new block, from hc's free list if possible.
func (hc *halfConn) newBlock() *block {
b := hc.bfree
if b == nil {
return new(block)
}
hc.bfree = b.link
b.link = nil
b.resize(0)
return b
}
// freeBlock returns a block to hc's free list.
// The protocol is such that each side only has a block or two on
// its free list at a time, so there's no need to worry about
// trimming the list, etc.
func (hc *halfConn) freeBlock(b *block) {
b.link = hc.bfree
hc.bfree = b
}
// splitBlock splits a block after the first n bytes,
// returning a block with those n bytes and a
// block with the remaindec. the latter may be nil.
func (hc *halfConn) splitBlock(b *block, n int) (*block, *block) {
if len(b.data) <= n {
return b, nil
}
bb := hc.newBlock()
bb.resize(len(b.data) - n)
copy(bb.data, b.data[n:])
b.data = b.data[0:n]
return b, bb
}
// readRecord reads the next TLS record from the connection
// and updates the record layer state.
// c.in.Mutex <= L; c.input == nil.
func (c *Conn) readRecord(want recordType) os.Error {
// Caller must be in sync with connection:
// handshake data if handshake not yet completed,
// else application data. (We don't support renegotiation.)
switch want {
default:
return c.sendAlert(alertInternalError)
case recordTypeHandshake, recordTypeChangeCipherSpec:
if c.handshakeComplete {
return c.sendAlert(alertInternalError)
}
case recordTypeApplicationData:
if !c.handshakeComplete {
return c.sendAlert(alertInternalError)
}
}
Again:
if c.rawInput == nil {
c.rawInput = c.in.newBlock()
}
b := c.rawInput
// Read header, payload.
if err := b.readFromUntil(c.conn, recordHeaderLen); err != nil {
// RFC suggests that EOF without an alertCloseNotify is
// an error, but popular web sites seem to do this,
// so we can't make it an error.
// if err == os.EOF {
// err = io.ErrUnexpectedEOF
// }
if e, ok := err.(net.Error); !ok || !e.Temporary() {
c.setError(err)
}
return err
}
typ := recordType(b.data[0])
vers := uint16(b.data[1])<<8 | uint16(b.data[2])
n := int(b.data[3])<<8 | int(b.data[4])
if c.haveVers && vers != c.vers {
return c.sendAlert(alertProtocolVersion)
}
if n > maxCiphertext {
return c.sendAlert(alertRecordOverflow)
}
if err := b.readFromUntil(c.conn, recordHeaderLen+n); err != nil {
if err == os.EOF {
err = io.ErrUnexpectedEOF
}
if e, ok := err.(net.Error); !ok || !e.Temporary() {
c.setError(err)
}
return err
}
// Process message.
b, c.rawInput = c.in.splitBlock(b, recordHeaderLen+n)
b.off = recordHeaderLen
if ok, err := c.in.decrypt(b); !ok {
return c.sendAlert(err)
}
data := b.data[b.off:]
if len(data) > maxPlaintext {
c.sendAlert(alertRecordOverflow)
c.in.freeBlock(b)
return c.error()
}
switch typ {
default:
c.sendAlert(alertUnexpectedMessage)
case recordTypeAlert:
if len(data) != 2 {
c.sendAlert(alertUnexpectedMessage)
break
}
if alert(data[1]) == alertCloseNotify {
c.setError(os.EOF)
break
}
switch data[0] {
case alertLevelWarning:
// drop on the floor
c.in.freeBlock(b)
goto Again
case alertLevelError:
c.setError(&net.OpError{Op: "remote error", Error: alert(data[1])})
default:
c.sendAlert(alertUnexpectedMessage)
}
case recordTypeChangeCipherSpec:
if typ != want || len(data) != 1 || data[0] != 1 {
c.sendAlert(alertUnexpectedMessage)
break
}
err := c.in.changeCipherSpec()
if err != nil {
c.sendAlert(err.(alert))
}
case recordTypeApplicationData:
if typ != want {
c.sendAlert(alertUnexpectedMessage)
break
}
c.input = b
b = nil
case recordTypeHandshake:
// TODO(rsc): Should at least pick off connection close.
if typ != want {
return c.sendAlert(alertNoRenegotiation)
}
c.hand.Write(data)
}
if b != nil {
c.in.freeBlock(b)
}
return c.error()
}
// sendAlert sends a TLS alert message.
// c.out.Mutex <= L.
func (c *Conn) sendAlertLocked(err alert) os.Error {
c.tmp[0] = alertLevelError
if err == alertNoRenegotiation {
c.tmp[0] = alertLevelWarning
}
c.tmp[1] = byte(err)
c.writeRecord(recordTypeAlert, c.tmp[0:2])
// closeNotify is a special case in that it isn't an error:
if err != alertCloseNotify {
return c.setError(&net.OpError{Op: "local error", Error: err})
}
return nil
}
// sendAlert sends a TLS alert message.
// L < c.out.Mutex.
func (c *Conn) sendAlert(err alert) os.Error {
c.out.Lock()
defer c.out.Unlock()
return c.sendAlertLocked(err)
}
// writeRecord writes a TLS record with the given type and payload
// to the connection and updates the record layer state.
// c.out.Mutex <= L.
func (c *Conn) writeRecord(typ recordType, data []byte) (n int, err os.Error) {
b := c.out.newBlock()
for len(data) > 0 {
m := len(data)
if m > maxPlaintext {
m = maxPlaintext
}
b.resize(recordHeaderLen + m)
b.data[0] = byte(typ)
vers := c.vers
if vers == 0 {
vers = maxVersion
}
b.data[1] = byte(vers >> 8)
b.data[2] = byte(vers)
b.data[3] = byte(m >> 8)
b.data[4] = byte(m)
copy(b.data[recordHeaderLen:], data)
c.out.encrypt(b)
_, err = c.conn.Write(b.data)
if err != nil {
break
}
n += m
data = data[m:]
}
c.out.freeBlock(b)
if typ == recordTypeChangeCipherSpec {
err = c.out.changeCipherSpec()
if err != nil {
// Cannot call sendAlert directly,
// because we already hold c.out.Mutex.
c.tmp[0] = alertLevelError
c.tmp[1] = byte(err.(alert))
c.writeRecord(recordTypeAlert, c.tmp[0:2])
c.err = &net.OpError{Op: "local error", Error: err}
return n, c.err
}
}
return
}
// readHandshake reads the next handshake message from
// the record layer.
// c.in.Mutex < L; c.out.Mutex < L.
func (c *Conn) readHandshake() (interface{}, os.Error) {
for c.hand.Len() < 4 {
if c.err != nil {
return nil, c.err
}
c.readRecord(recordTypeHandshake)
}
data := c.hand.Bytes()
n := int(data[1])<<16 | int(data[2])<<8 | int(data[3])
if n > maxHandshake {
c.sendAlert(alertInternalError)
return nil, c.err
}
for c.hand.Len() < 4+n {
if c.err != nil {
return nil, c.err
}
c.readRecord(recordTypeHandshake)
}
data = c.hand.Next(4 + n)
var m handshakeMessage
switch data[0] {
case typeClientHello:
m = new(clientHelloMsg)
case typeServerHello:
m = new(serverHelloMsg)
case typeCertificate:
m = new(certificateMsg)
case typeCertificateRequest:
m = new(certificateRequestMsg)
case typeCertificateStatus:
m = new(certificateStatusMsg)
case typeServerHelloDone:
m = new(serverHelloDoneMsg)
case typeClientKeyExchange:
m = new(clientKeyExchangeMsg)
case typeCertificateVerify:
m = new(certificateVerifyMsg)
case typeNextProtocol:
m = new(nextProtoMsg)
case typeFinished:
m = new(finishedMsg)
default:
c.sendAlert(alertUnexpectedMessage)
return nil, alertUnexpectedMessage
}
// The handshake message unmarshallers
// expect to be able to keep references to data,
// so pass in a fresh copy that won't be overwritten.
data = append([]byte(nil), data...)
if !m.unmarshal(data) {
c.sendAlert(alertUnexpectedMessage)
return nil, alertUnexpectedMessage
}
return m, nil
}
// Write writes data to the connection.
func (c *Conn) Write(b []byte) (n int, err os.Error) {
if err = c.Handshake(); err != nil {
return
}
c.out.Lock()
defer c.out.Unlock()
if !c.handshakeComplete {
return 0, alertInternalError
}
if c.err != nil {
return 0, c.err
}
return c.writeRecord(recordTypeApplicationData, b)
}
// Read can be made to time out and return err == os.EAGAIN
// after a fixed time limit; see SetTimeout and SetReadTimeout.
func (c *Conn) Read(b []byte) (n int, err os.Error) {
if err = c.Handshake(); err != nil {
return
}
c.in.Lock()
defer c.in.Unlock()
for c.input == nil && c.err == nil {
if err := c.readRecord(recordTypeApplicationData); err != nil {
// Soft error, like EAGAIN
return 0, err
}
}
if c.err != nil {
return 0, c.err
}
n, err = c.input.Read(b)
if c.input.off >= len(c.input.data) {
c.in.freeBlock(c.input)
c.input = nil
}
return n, nil
}
// Close closes the connection.
func (c *Conn) Close() os.Error {
if err := c.Handshake(); err != nil {
return err
}
return c.sendAlert(alertCloseNotify)
}
// Handshake runs the client or server handshake
// protocol if it has not yet been run.
// Most uses of this package need not call Handshake
// explicitly: the first Read or Write will call it automatically.
func (c *Conn) Handshake() os.Error {
c.handshakeMutex.Lock()
defer c.handshakeMutex.Unlock()
if err := c.error(); err != nil {
return err
}
if c.handshakeComplete {
return nil
}
if c.isClient {
return c.clientHandshake()
}
return c.serverHandshake()
}
// ConnectionState returns basic TLS details about the connection.
func (c *Conn) ConnectionState() ConnectionState {
c.handshakeMutex.Lock()
defer c.handshakeMutex.Unlock()
var state ConnectionState
state.HandshakeComplete = c.handshakeComplete
if c.handshakeComplete {
state.NegotiatedProtocol = c.clientProtocol
state.CipherSuite = c.cipherSuite
}
return state
}
// OCSPResponse returns the stapled OCSP response from the TLS server, if
// any. (Only valid for client connections.)
func (c *Conn) OCSPResponse() []byte {
c.handshakeMutex.Lock()
defer c.handshakeMutex.Unlock()
return c.ocspResponse
}
// PeerCertificates returns the certificate chain that was presented by the
// other side.
func (c *Conn) PeerCertificates() []*x509.Certificate {
c.handshakeMutex.Lock()
defer c.handshakeMutex.Unlock()
return c.peerCertificates
}
// VerifyHostname checks that the peer certificate chain is valid for
// connecting to host. If so, it returns nil; if not, it returns an os.Error
// describing the problem.
func (c *Conn) VerifyHostname(host string) os.Error {
c.handshakeMutex.Lock()
defer c.handshakeMutex.Unlock()
if !c.isClient {
return os.ErrorString("VerifyHostname called on TLS server connection")
}
if !c.handshakeComplete {
return os.ErrorString("TLS handshake has not yet been performed")
}
return c.peerCertificates[0].VerifyHostname(host)
}