REALITY protocol: Remove ChaCha20-Poly1305 support for REALITY's session id auth

#3813 (comment)

XTLS/REALITY#4 (comment)

Reverts 65b467e

Author: RPRX

go.mod

@@ -20,7 +20,7 @@ require (
 	github.com/stretchr/testify v1.10.0
 	github.com/v2fly/ss-bloomring v0.0.0-20210312155135-28617310f63e
 	github.com/vishvananda/netlink v1.3.1
-	github.com/xtls/reality v0.0.0-20250513125209-514f8647eac0
+	github.com/xtls/reality v0.0.0-20250516070713-4df2ec9a5b47
 	go4.org/netipx v0.0.0-20231129151722-fdeea329fbba
 	golang.org/x/crypto v0.38.0
 	golang.org/x/net v0.40.0

go.sum

@@ -76,10 +76,8 @@ github.com/vishvananda/netlink v1.3.1 h1:3AEMt62VKqz90r0tmNhog0r/PpWKmrEShJU0wJW
 github.com/vishvananda/netlink v1.3.1/go.mod h1:ARtKouGSTGchR8aMwmkzC0qiNPrrWO5JS/XMVl45+b4=
 github.com/vishvananda/netns v0.0.5 h1:DfiHV+j8bA32MFM7bfEunvT8IAqQ/NzSJHtcmW5zdEY=
 github.com/vishvananda/netns v0.0.5/go.mod h1:SpkAiCQRtJ6TvvxPnOSyH3BMl6unz3xZlaprSwhNNJM=
-github.com/xtls/reality v0.0.0-20240712055506-48f0b2d5ed6d h1:+B97uD9uHLgAAulhigmys4BVwZZypzK7gPN3WtpgRJg=
-github.com/xtls/reality v0.0.0-20240712055506-48f0b2d5ed6d/go.mod h1:dm4y/1QwzjGaK17ofi0Vs6NpKAHegZky8qk6J2JJZAE=
-github.com/xtls/reality v0.0.0-20250513125209-514f8647eac0 h1:ou6jXqJ9Ogs0BaEIzuszo1HMBokiKpf7XpNdsVYcvfA=
-github.com/xtls/reality v0.0.0-20250513125209-514f8647eac0/go.mod h1:bJdU3ExzfUlY40Xxfibq3THW9IHiE8mHu/tEzud5JWM=
+github.com/xtls/reality v0.0.0-20250516070713-4df2ec9a5b47 h1:9aJWkgWBwZ83l3j7+hBh3SurvRKuNfCgsSner5n6BcM=
+github.com/xtls/reality v0.0.0-20250516070713-4df2ec9a5b47/go.mod h1:bJdU3ExzfUlY40Xxfibq3THW9IHiE8mHu/tEzud5JWM=
 github.com/yuin/goldmark v1.4.1/go.mod h1:mwnBkeHKe2W/ZEtQ+71ViKU8L12m81fl3OWwC1Zlc8k=
 go.opentelemetry.io/auto/sdk v1.1.0 h1:cH53jehLUN6UFLY71z+NDOiNJqDdPRaXzTel0sJySYA=
 go.opentelemetry.io/auto/sdk v1.1.0/go.mod h1:3wSPjt5PWp2RhlCcmmOial7AvC4DQqZb7a7wCow3W8A=

transport/internet/reality/reality.go

@@ -30,14 +30,10 @@ import (
 	"github.com/xtls/xray-core/common/net"
 	"github.com/xtls/xray-core/core"
 	"github.com/xtls/xray-core/transport/internet/tls"
-	"golang.org/x/crypto/chacha20poly1305"
 	"golang.org/x/crypto/hkdf"
 	"golang.org/x/net/http2"
 )
 
-//go:linkname aesgcmPreferred github.com/refraction-networking/utls.aesgcmPreferred
-func aesgcmPreferred(ciphers []uint16) bool
-
 type Conn struct {
 	*reality.Conn
 }
@@ -147,13 +143,8 @@ func UClient(c net.Conn, config *Config, ctx context.Context, dest net.Destinati
 		if _, err := hkdf.New(sha256.New, uConn.AuthKey, hello.Random[:20], []byte("REALITY")).Read(uConn.AuthKey); err != nil {
 			return nil, err
 		}
-		var aead cipher.AEAD
-		if aesgcmPreferred(hello.CipherSuites) {
-			block, _ := aes.NewCipher(uConn.AuthKey)
-			aead, _ = cipher.NewGCM(block)
-		} else {
-			aead, _ = chacha20poly1305.New(uConn.AuthKey)
-		}
+		block, _ := aes.NewCipher(uConn.AuthKey)
+		aead, _ := cipher.NewGCM(block)
 		if config.Show {
 			errors.LogInfo(ctx, fmt.Sprintf("REALITY localAddr: %v\tuConn.AuthKey[:16]: %v\tAEAD: %T\n", localAddr, uConn.AuthKey[:16], aead))
 		}