From b1b2572d5bd9d991adf0b326496e6c823ef74183 Mon Sep 17 00:00:00 2001
From: Vinicius Fortuna <fortuna@users.noreply.github.com>
Date: Fri, 23 Oct 2020 22:23:58 -0400
Subject: [PATCH] Fix key derivation

---
 shadowsocks/cipher.go             | 18 ++++++++-
 shadowsocks/compatibility_test.go | 65 +++++++++++++++++++++++++++++++
 2 files changed, 82 insertions(+), 1 deletion(-)
 create mode 100644 shadowsocks/compatibility_test.go

diff --git a/shadowsocks/cipher.go b/shadowsocks/cipher.go
index be97bbb6..837770b3 100644
--- a/shadowsocks/cipher.go
+++ b/shadowsocks/cipher.go
@@ -17,6 +17,7 @@ package shadowsocks
 import (
 	"crypto/aes"
 	"crypto/cipher"
+	"crypto/md5"
 	"crypto/sha1"
 	"fmt"
 	"io"
@@ -115,13 +116,28 @@ func (c *Cipher) NewAEAD(salt []byte) (cipher.AEAD, error) {
 	return c.aead.newInstance(sessionKey)
 }
 
+// Function definition at https://www.openssl.org/docs/manmaster/man3/EVP_BytesToKey.html
+func simpleEVPBytesToKey(data []byte, keyLen int) []byte {
+	var derived, di []byte
+	h := md5.New()
+	for len(derived) < keyLen {
+		h.Write(di)
+		h.Write(data)
+		derived = h.Sum(derived)
+		di = derived[len(derived)-h.Size():]
+		h.Reset()
+	}
+	return derived[:keyLen]
+}
+
 // NewCipher creates a Cipher given a cipher name and a secret
 func NewCipher(cipherName string, secretText string) (*Cipher, error) {
-	secret := []byte(secretText)
 	aeadSpec, err := getAEADSpec(cipherName)
 	if err != nil {
 		return nil, err
 	}
+	// Key derivation as per https://shadowsocks.org/en/spec/AEAD-Ciphers.html
+	secret := simpleEVPBytesToKey([]byte(secretText), aeadSpec.keySize)
 	return &Cipher{*aeadSpec, secret}, nil
 }
 
diff --git a/shadowsocks/compatibility_test.go b/shadowsocks/compatibility_test.go
new file mode 100644
index 00000000..df38a0c2
--- /dev/null
+++ b/shadowsocks/compatibility_test.go
@@ -0,0 +1,65 @@
+// Copyright 2020 Jigsaw Operations LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package shadowsocks
+
+import (
+	"io"
+	"net"
+	"sync"
+	"testing"
+
+	"github.com/shadowsocks/go-shadowsocks2/core"
+	"github.com/shadowsocks/go-shadowsocks2/shadowaead"
+	"github.com/stretchr/testify/require"
+)
+
+func TestCompatibility(t *testing.T) {
+	cipherName := "chacha20-ietf-poly1305"
+	secret := "secret"
+	toRight := "payload1"
+	fromRight := "payload2"
+	left, right := net.Pipe()
+
+	var wait sync.WaitGroup
+	wait.Add(1)
+	go func() {
+		cipher, err := NewCipher(cipherName, secret)
+		require.Nil(t, err, "NewCipher failed: %v", err)
+		ssWriter := NewShadowsocksWriter(left, cipher)
+		ssWriter.Write([]byte(toRight))
+
+		ssReader := NewShadowsocksReader(left, cipher)
+		output := make([]byte, len(fromRight))
+		_, err = ssReader.Read(output)
+		require.Nil(t, err, "Read failed: %v", err)
+		require.Equal(t, fromRight, string(output))
+		left.Close()
+		wait.Done()
+	}()
+
+	otherCipher, err := core.PickCipher(cipherName, []byte{}, secret)
+	require.Nil(t, err)
+	conn := shadowaead.NewConn(right, otherCipher.(shadowaead.Cipher))
+	output := make([]byte, len(toRight))
+	_, err = io.ReadFull(conn, output)
+	require.Nil(t, err)
+	require.Equal(t, toRight, string(output))
+
+	_, err = conn.Write([]byte(fromRight))
+	require.Nil(t, err, "Write failed: %v", err)
+
+	conn.Close()
+	wait.Wait()
+}