Cloak/internal/client/TLS.go

package client

import (
	"github.com/cbeuw/Cloak/internal/common"
	utls "github.com/refraction-networking/utls"
	log "github.com/sirupsen/logrus"
	"net"
	"strings"
)

const appDataMaxLength = 16401

type clientHelloFields struct {
	random         []byte
	sessionId      []byte
	x25519KeyShare []byte
	serverName     string
}

type browser int

const (
	chrome = iota
	firefox
	safari
)

type DirectTLS struct {
	*common.TLSConn
	browser browser
}

var topLevelDomains = []string{"com", "net", "org", "it", "fr", "me", "ru", "cn", "es", "tr", "top", "xyz", "info"}

func randomServerName() string {
	/*
		Copyright: Proton AG
		https://github.com/ProtonVPN/wireguard-go/commit/bcf344b39b213c1f32147851af0d2a8da9266883

		Permission is hereby granted, free of charge, to any person obtaining a copy of
		this software and associated documentation files (the "Software"), to deal in
		the Software without restriction, including without limitation the rights to
		use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
		of the Software, and to permit persons to whom the Software is furnished to do
		so, subject to the following conditions:

		The above copyright notice and this permission notice shall be included in all
		copies or substantial portions of the Software.

		THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
		IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
		FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
		AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
		LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
		OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
		SOFTWARE.
	*/
	charNum := int('z') - int('a') + 1
	size := 3 + common.RandInt(10)
	name := make([]byte, size)
	for i := range name {
		name[i] = byte(int('a') + common.RandInt(charNum))
	}
	return string(name) + "." + common.RandItem(topLevelDomains)
}

func buildClientHello(browser browser, fields clientHelloFields) ([]byte, error) {
	// We don't use utls to handle connections (as it'll attempt a real TLS negotiation)
	// We only want it to build the ClientHello locally
	fakeConn := net.TCPConn{}
	var helloID utls.ClientHelloID
	switch browser {
	case chrome:
		helloID = utls.HelloChrome_Auto
	case firefox:
		helloID = utls.HelloFirefox_Auto
	case safari:
		helloID = utls.HelloSafari_Auto
	}

	uclient := utls.UClient(&fakeConn, &utls.Config{ServerName: fields.serverName}, helloID)
	if err := uclient.BuildHandshakeState(); err != nil {
		return []byte{}, err
	}
	if err := uclient.SetClientRandom(fields.random); err != nil {
		return []byte{}, err
	}

	uclient.HandshakeState.Hello.SessionId = make([]byte, 32)
	copy(uclient.HandshakeState.Hello.SessionId, fields.sessionId)

	// Find the X25519 key share and overwrite it
	var extIndex int
	var keyShareIndex int
	for i, ext := range uclient.Extensions {
		ext, ok := ext.(*utls.KeyShareExtension)
		if ok {
			extIndex = i
			for j, keyShare := range ext.KeyShares {
				if keyShare.Group == utls.X25519 {
					keyShareIndex = j
				}
			}
		}
	}
	copy(uclient.Extensions[extIndex].(*utls.KeyShareExtension).KeyShares[keyShareIndex].Data, fields.x25519KeyShare)

	if err := uclient.BuildHandshakeState(); err != nil {
		return []byte{}, err
	}
	return uclient.HandshakeState.Hello.Raw, nil
}

// Handshake handles the TLS handshake for a given conn and returns the sessionKey
// if the server proceed with Cloak authentication
func (tls *DirectTLS) Handshake(rawConn net.Conn, authInfo AuthInfo) (sessionKey [32]byte, err error) {
	payload, sharedSecret := makeAuthenticationPayload(authInfo)

	fields := clientHelloFields{
		random:         payload.randPubKey[:],
		sessionId:      payload.ciphertextWithTag[0:32],
		x25519KeyShare: payload.ciphertextWithTag[32:64],
		serverName:     authInfo.MockDomain,
	}

	if strings.EqualFold(fields.serverName, "random") {
		fields.serverName = randomServerName()
	}

	var ch []byte
	ch, err = buildClientHello(tls.browser, fields)
	if err != nil {
		return
	}
	chWithRecordLayer := common.AddRecordLayer(ch, common.Handshake, common.VersionTLS11)
	_, err = rawConn.Write(chWithRecordLayer)
	if err != nil {
		return
	}
	log.Trace("client hello sent successfully")
	tls.TLSConn = common.NewTLSConn(rawConn)

	buf := make([]byte, 1024)
	log.Trace("waiting for ServerHello")
	_, err = tls.Read(buf)
	if err != nil {
		return
	}

	encrypted := append(buf[6:38], buf[84:116]...)
	nonce := encrypted[0:12]
	ciphertextWithTag := encrypted[12:60]
	sessionKeySlice, err := common.AESGCMDecrypt(nonce, sharedSecret[:], ciphertextWithTag)
	if err != nil {
		return
	}
	copy(sessionKey[:], sessionKeySlice)

	for i := 0; i < 2; i++ {
		// ChangeCipherSpec and EncryptedCert (in the format of application data)
		_, err = tls.Read(buf)
		if err != nil {
			return
		}
	}
	return sessionKey, nil

}