Shadowsockets Reduecd IV Head Entropy Experiment

proxy/shadowsocks/config.go

@@ -25,6 +25,8 @@ type MemoryAccount struct {
 	Key    []byte
 
 	replayFilter antireplay.GeneralizedReplayFilter
+
+	ReducedIVEntropy bool
 }
 
 // Equals implements protocol.Account.Equals().
@@ -101,6 +103,7 @@ func (a *Account) AsAccount() (protocol.Account, error) {
 			}
 			return nil
 		}(),
+		ReducedIVEntropy: a.ExperimentReducedIvHeadEntropy,
 	}, nil
 }
 

proxy/shadowsocks/config.proto

@@ -16,6 +16,7 @@ message Account {
   CipherType cipher_type = 2;
 
   bool iv_check = 3;
+  bool experiment_reduced_iv_head_entropy = 90001;
 }
 
 enum CipherType {

proxy/shadowsocks/protocol.go

@@ -6,6 +6,7 @@ import (
 	"crypto/sha256"
 	"hash/crc32"
 	"io"
+	mrand "math/rand"
 	gonet "net"
 
 	"github.com/v2fly/v2ray-core/v5/common"
@@ -103,6 +104,9 @@ func WriteTCPRequest(request *protocol.RequestHeader, writer io.Writer) (buf.Wri
 	if account.Cipher.IVSize() > 0 {
 		iv = make([]byte, account.Cipher.IVSize())
 		common.Must2(rand.Read(iv))
+		if account.ReducedIVEntropy {
+			remapToPrintable(iv[:6])
+		}
 		if ivError := account.CheckIV(iv); ivError != nil {
 			return nil, newError("failed to mark outgoing iv").Base(ivError)
 		}
@@ -301,3 +305,11 @@ func (w *UDPWriter) WriteTo(payload []byte, addr gonet.Addr) (n int, err error)
 	packet.Release()
 	return len(payload), err
 }
+
+func remapToPrintable(input []byte) {
+	const charSet = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789!#$%&()*+,./:;<=>?@[]^_`{|}~\\\""
+	seed := mrand.New(mrand.NewSource(int64(crc32.ChecksumIEEE(input))))
+	for i := range input {
+		input[i] = charSet[seed.Intn(len(charSet))]
+	}
+}

proxy/shadowsocks/simplified/config.go

@@ -37,8 +37,9 @@ func init() {
 					User: []*protocol.User{
 						{
 							Account: serial.ToTypedMessage(&shadowsocks.Account{
-								Password:   simplifiedClient.Password,
-								CipherType: shadowsocks.CipherFromString(simplifiedClient.Method),
+								Password:                       simplifiedClient.Password,
+								CipherType:                     shadowsocks.CipherFromString(simplifiedClient.Method),
+								ExperimentReducedIvHeadEntropy: simplifiedClient.ExperimentReducedIvHeadEntropy,
 							}),
 						},
 					},

proxy/shadowsocks/simplified/config.proto

@@ -28,4 +28,5 @@ message ClientConfig {
   uint32 port = 2;
   string method = 3;
   string password = 4;
+  bool experiment_reduced_iv_head_entropy = 90001;
 }