1 files changed, 801 insertions, 0 deletions
diff --git a/libgo/go/crypto/tls/conn.go b/libgo/go/crypto/tls/conn.go
new file mode 100644
index 000000000..d203e8d51
--- /dev/null
+++ b/libgo/go/crypto/tls/conn.go
@@ -0,0 +1,801 @@
+// 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 typeServerKeyExchange:
+		m = new(serverKeyExchangeMsg)
+	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)
+}