Simple method for IdentifyModernFingerprint

record_detect.go

@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"io"
 	"net"
+	"slices"
 	"sync"
 	"time"
 
@@ -108,6 +109,35 @@ func (c *DetectConn) Read(b []byte) (n int, err error) {
 	return 0, io.EOF
 }
 
+func IdentifyModernFingerprint(ch *clientHelloMsg) string {
+	if slices.Contains(ch.supportedVersions, VersionTLS10) && slices.Contains(ch.supportedVersions, VersionTLS11) {
+		if slices.Contains(ch.extensions, utlsExtensionApplicationSettings) {
+			return "hellochrome_96"
+		}
+		return "hellochrome_87" // also hellochrome_83
+	}
+	if slices.Contains(ch.supportedCurves, X25519MLKEM768) {
+		if slices.Contains(ch.extensions, utlsExtensionApplicationSettingsNew) {
+			return "hellochrome_133"
+		}
+		return "hellochrome_131"
+	}
+	if slices.Contains(ch.extensions, utlsExtensionECH) {
+		return "hellochrome_120"
+	}
+	if slices.Contains(ch.extensions, utlsExtensionPadding) {
+		return "hellochrome_106_shuffle" // also HelloChrome_100, HelloChrome_102
+	}
+	return "Custom"
+}
+
+const (
+	utlsExtensionPadding                uint16 = 21
+	utlsExtensionApplicationSettings    uint16 = 17513  // not IANA assigned
+	utlsExtensionApplicationSettingsNew uint16 = 17613  // not IANA assigned
+	utlsExtensionECH                    uint16 = 0xfe0d // draft-ietf-tls-esni-17
+)
+
 var ModernFingerprints = map[string]*utls.ClientHelloID{
 	// One of these will be chosen as `random` at startup
 	"hellofirefox_99":         &utls.HelloFirefox_99,

tls.go

@@ -162,8 +162,6 @@ func Value(vals ...byte) (value int) {
 // The configuration config must be non-nil and must include
 // at least one certificate or else set GetCertificate.
 func Server(ctx context.Context, conn net.Conn, config *Config) (*Conn, error) {
-	postHandshakeRecordsLens := DetectPostHandshakeRecordsLens(config, "hellochrome_131")
-
 	remoteAddr := conn.RemoteAddr().String()
 	if config.Show {
 		fmt.Printf("REALITY remoteAddr: %v\n", remoteAddr)
@@ -374,6 +372,12 @@ func Server(ctx context.Context, conn net.Conn, config *Config) (*Conn, error) {
 			if err != nil {
 				break
 			}
+			var fingerprint = IdentifyModernFingerprint(hs.clientHello)
+			fmt.Printf("REALITY remoteAddr: %v\tidentified fingerprint: %v\n", remoteAddr, fingerprint)
+			if fingerprint == "Custom" {
+				fingerprint = "hellochrome_131"
+			}
+			postHandshakeRecordsLens := DetectPostHandshakeRecordsLens(config, fingerprint)
 			for _, length := range postHandshakeRecordsLens[hs.clientHello.serverName] {
 				if length == 0 {
 					break;