Merge pull request #242 from notsure2/random-sni

Support ServerName randomization (by setting ServerName=random) using ProtonVPN algo

README.md

@@ -137,7 +137,7 @@ random-like. **You may only leave it as `plain` if you are certain that your und
 encryption and authentication (via AEAD or similar techniques).**
 
 `ServerName` is the domain you want to make your ISP or firewall _think_ you are visiting. Ideally it should
-match `RedirAddr` in the server's configuration, a major site the censor allows, but it doesn't have to.
+match `RedirAddr` in the server's configuration, a major site the censor allows, but it doesn't have to. Use `random` to randomize the server name for every connection made.
 
 `AlternativeNames` is an array used alongside `ServerName` to shuffle between different ServerNames for every new
 connection. **This may conflict with `CDN` Transport mode** if the CDN provider prohibits domain fronting and rejects

internal/client/TLS.go

@@ -1,11 +1,11 @@
 package client
 
 import (
+	"github.com/cbeuw/Cloak/internal/common"
 	utls "github.com/refraction-networking/utls"
 	log "github.com/sirupsen/logrus"
 	"net"
-
-	"github.com/cbeuw/Cloak/internal/common"
+	"strings"
 )
 
 const appDataMaxLength = 16401
@@ -30,6 +30,40 @@ type DirectTLS struct {
 	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
@@ -89,6 +123,10 @@ func (tls *DirectTLS) Handshake(rawConn net.Conn, authInfo AuthInfo) (sessionKey
 		serverName:     authInfo.MockDomain,
 	}
 
+	if strings.EqualFold(fields.serverName, "random") {
+		fields.serverName = randomServerName()
+	}
+
 	var ch []byte
 	ch, err = buildClientHello(tls.browser, fields)
 	if err != nil {

internal/common/crypto.go

@@ -6,6 +6,7 @@ import (
 	"crypto/rand"
 	"errors"
 	"io"
+	"math/big"
 	"time"
 
 	log "github.com/sirupsen/logrus"
@@ -52,21 +53,45 @@ func CryptoRandRead(buf []byte) {
 	RandRead(rand.Reader, buf)
 }
 
-func RandRead(randSource io.Reader, buf []byte) {
-	_, err := randSource.Read(buf)
+func backoff(f func() error) {
+	err := f()
 	if err == nil {
 		return
 	}
 	waitDur := [10]time.Duration{5 * time.Millisecond, 10 * time.Millisecond, 30 * time.Millisecond, 50 * time.Millisecond,
 		100 * time.Millisecond, 300 * time.Millisecond, 500 * time.Millisecond, 1 * time.Second,
 		3 * time.Second, 5 * time.Second}
 	for i := 0; i < 10; i++ {
-		log.Errorf("Failed to get random bytes: %v. Retrying...", err)
-		_, err = randSource.Read(buf)
+		log.Errorf("Failed to get random: %v. Retrying...", err)
+		err = f()
 		if err == nil {
 			return
 		}
 		time.Sleep(waitDur[i])
 	}
-	log.Fatal("Cannot get random bytes after 10 retries")
+	log.Fatal("Cannot get random after 10 retries")
+}
+
+func RandRead(randSource io.Reader, buf []byte) {
+	backoff(func() error {
+		_, err := randSource.Read(buf)
+		return err
+	})
+}
+
+func RandItem[T any](list []T) T {
+	return list[RandInt(len(list))]
+}
+
+func RandInt(n int) int {
+	s := new(int)
+	backoff(func() error {
+		size, err := rand.Int(rand.Reader, big.NewInt(int64(n)))
+		if err != nil {
+			return err
+		}
+		*s = int(size.Int64())
+		return nil
+	})
+	return *s
 }