Message decoding test done

Api_request.txt

@@ -211,4 +211,11 @@ X-Forwarded-Server: wechat.hitxy.org.au
     <Content><![CDATA[songbook]]></Content>
     <MsgId>6411651983041024410</MsgId>
     <Encrypt><![CDATA[3muEH/vxWRf76hHB+G4WB744Ho4Fu4RmpYYwd3R0Ek//h3dZDmuzakVztD2ecG8lB0DKV9EAJHaSp/Q4nLQM36Dg9eQQb888e6Z6nyjMX/2Na8upraDHrfR2oW1Gv8AJ0bzrYKubpk7AYtvlvNpnhQ2kDKhn5v1L/Rd8CRSb5ODJ3xDhqQqYd6R4DTr4SF8ofCrqDp0taYkMt4e0eHuCDEp+/A/PLBX1PL8Xw+kv/7eW/aoJQIapXAGMgf61/Qj9RfFmNDG6hKz1bF4CU2u/y4XV63xBepDQ7ZfOmtfALa1pIQGhHzyf5jReArmkLu4yERBzQYwc8G5eDq2WDQrrwaaiaVYo1SDNk0F88zjENobf9I+9lVAFbCly4vhdtlLbRHrUomiAjgzN3nHTza9E6NdCpsJ46C8l+1u/3H7Vq0g=]]></Encrypt>
+</xml>
+
+
+如果纯粹加密，没有明文
+<xml>
+    <ToUserName><![CDATA[gh_f09231355c68]]></ToUserName>
+    <Encrypt><![CDATA[P2DoRtilYwJ1aM+VW1sGs6p11Rhcd/TrFYtvsw53SUVw2Knh27hF5IZUBxRXbz+k87zy983ec5aOwgS+WxYoejmGubaqiYy2yfCBNyGRlWfe+iWc2TnvPIEAJebSWuNOJ7FoITeMndr4tW391XxDdMom8I/VsqKnsZZAangUsxmA1ZEnP/d4Lx8/xt3qJKrJMa4Q8s9VsOOvzLIGhL1IN5bHaXN+CwgBTAUCrHD8AneiX5MLSv/74qozg+jKBSUebZrjRYuTymQ3TBh3pQXyRBQTZNrCAe1tlcNli9e5MSUMsHFIzGw/kiu93/5VkxCYRLgRDQKl9oam4+Rpxywir7EiT7I4X343l9ogcMLWX16evkLlQHoqBhLl6ZcfW7Nmq8/Ghy8jbuwqkR/0jLJ/avtjzgJOwaxdBUz4nYZ452rLJekxIvsmV6PZgCXRrKHzmpZX+i6hIRIWiIaDeMOEsw==]]></Encrypt>
 </xml>

main.go

@@ -16,6 +16,9 @@ func main() {
 		log.Fatal("unable to read config, program quit")
 		return
 	}
+
+	Decode("SS")
+	return
 	//setup handler
 	http.HandleFunc("/", webrootHandler)
 	http.HandleFunc("/api", apiV1Main)

messageEncrypt.go

@@ -0,0 +1,151 @@
+package main
+
+import (
+	"crypto/aes"
+	"crypto/cipher"
+	"encoding/base64"
+	"fmt"
+)
+
+const txt = "P2DoRtilYwJ1aM+VW1sGs6p11Rhcd/TrFYtvsw53SUVw2Knh27hF5IZUBxRXbz+k87zy983ec5aOwgS+WxYoejmGubaqiYy2yfCBNyGRlWfe+iWc2TnvPIEAJebSWuNOJ7FoITeMndr4tW391XxDdMom8I/VsqKnsZZAangUsxmA1ZEnP/d4Lx8/xt3qJKrJMa4Q8s9VsOOvzLIGhL1IN5bHaXN+CwgBTAUCrHD8AneiX5MLSv/74qozg+jKBSUebZrjRYuTymQ3TBh3pQXyRBQTZNrCAe1tlcNli9e5MSUMsHFIzGw/kiu93/5VkxCYRLgRDQKl9oam4+Rpxywir7EiT7I4X343l9ogcMLWX16evkLlQHoqBhLl6ZcfW7Nmq8/Ghy8jbuwqkR/0jLJ/avtjzgJOwaxdBUz4nYZ452rLJekxIvsmV6PZgCXRrKHzmpZX+i6hIRIWiIaDeMOEsw=="
+
+//Decode  Decode encrypt string to xml context
+func Decode(s string) string {
+
+	r, _ := base64.StdEncoding.DecodeString(txt)
+
+	key, _ := base64.StdEncoding.DecodeString(APIConfig.EncodingAESKey + "=")
+	var k [32]byte
+	copy(k[:], key)
+	random, raw, err := AESDecryptMsg([]byte(r), APIConfig.Appid, k)
+
+	fmt.Println(len(txt))
+	fmt.Println(random)
+	fmt.Println(string(raw))
+
+	bc, err := aes.NewCipher([]byte(key))
+	if err == nil {
+		fmt.Printf("The block size is %d\n", bc.BlockSize())
+		var decoded = make([]byte, 4096)
+		bc.Decrypt(decoded, r)
+		//AES Decode
+	}
+	fmt.Printf("%s", string(r))
+	return string(r)
+}
+
+// 把整数 n 格式化成 4 字节的网络字节序
+func encodeNetworkBytesOrder(orderBytes []byte, n int) {
+	if len(orderBytes) != 4 {
+		panic("the length of orderBytes must be equal to 4")
+	}
+	orderBytes[0] = byte(n >> 24)
+	orderBytes[1] = byte(n >> 16)
+	orderBytes[2] = byte(n >> 8)
+	orderBytes[3] = byte(n)
+}
+
+// 从 4 字节的网络字节序里解析出整数
+func decodeNetworkBytesOrder(orderBytes []byte) (n int) {
+	if len(orderBytes) != 4 {
+		panic("the length of orderBytes must be equal to 4")
+	}
+	n = int(orderBytes[0])<<24 |
+		int(orderBytes[1])<<16 |
+		int(orderBytes[2])<<8 |
+		int(orderBytes[3])
+	return
+}
+
+//AESEncryptMsg encryptedMsg = AES_Encrypt[random(16B) + msg_len(4B) + rawXMLMsg + AppId]
+func AESEncryptMsg(random, rawXMLMsg []byte, AppId string, AESKey [32]byte) (encryptedMsg []byte) {
+	const BLOCK_SIZE = 32 // PKCS#7
+
+	buf := make([]byte, 20+len(rawXMLMsg)+len(AppId)+BLOCK_SIZE)
+	plain := buf[:20]
+	pad := buf[len(buf)-BLOCK_SIZE:]
+
+	// 拼接
+	copy(plain, random)
+	encodeNetworkBytesOrder(plain[16:20], len(rawXMLMsg))
+	plain = append(plain, rawXMLMsg...)
+	plain = append(plain, AppId...)
+
+	// PKCS#7 补位
+	amountToPad := BLOCK_SIZE - len(plain)%BLOCK_SIZE
+	for i := 0; i < amountToPad; i++ {
+		pad[i] = byte(amountToPad)
+	}
+	plain = buf[:len(plain)+amountToPad]
+
+	// 加密
+	block, err := aes.NewCipher(AESKey[:])
+	if err != nil {
+		panic(err)
+	}
+	mode := cipher.NewCBCEncrypter(block, AESKey[:16])
+	mode.CryptBlocks(plain, plain)
+
+	encryptedMsg = plain
+	return
+}
+
+// encryptedMsg = AES_Encrypt[random(16B) + msg_len(4B) + rawXMLMsg + AppId]
+func AESDecryptMsg(encryptedMsg []byte, AppId string, AESKey [32]byte) (random, rawXMLMsg []byte, err error) {
+	const BLOCK_SIZE = 32 // PKCS#7
+
+	if len(encryptedMsg) < BLOCK_SIZE {
+		err = fmt.Errorf("the length of encryptedMsg too short: %d", len(encryptedMsg))
+		return
+	}
+	if len(encryptedMsg)%BLOCK_SIZE != 0 {
+		err = fmt.Errorf("encryptedMsg is not a multiple of the block size, the length is %d", len(encryptedMsg))
+		return
+	}
+
+	plain := make([]byte, len(encryptedMsg)) // len(plain) >= BLOCK_SIZE
+
+	// 解密
+	block, err := aes.NewCipher(AESKey[:])
+	if err != nil {
+		panic(err)
+	}
+	mode := cipher.NewCBCDecrypter(block, AESKey[:16])
+	mode.CryptBlocks(plain, encryptedMsg)
+
+	// PKCS#7 去除补位
+	amountToPad := int(plain[len(plain)-1])
+	if amountToPad < 1 || amountToPad > BLOCK_SIZE {
+		err = fmt.Errorf("the amount to pad is invalid: %d", amountToPad)
+		return
+	}
+	plain = plain[:len(plain)-amountToPad]
+
+	// 反拼装
+	// len(plain) == 16+4+len(rawXMLMsg)+len(AppId)
+	// len(AppId) > 0
+	if len(plain) <= 20 {
+		err = fmt.Errorf("plain msg too short, the length is %d", len(plain))
+		return
+	}
+	msgLen := decodeNetworkBytesOrder(plain[16:20])
+	if msgLen < 0 {
+		err = fmt.Errorf("invalid msg length: %d", msgLen)
+		return
+	}
+	msgEnd := 20 + msgLen
+	if len(plain) <= msgEnd {
+		err = fmt.Errorf("msg length too large: %d", msgLen)
+		return
+	}
+
+	AppIdHave := string(plain[msgEnd:])
+	if AppIdHave != AppId { // crypto/subtle.ConstantTimeCompare ???
+		err = fmt.Errorf("AppId mismatch, have: %s, want: %s", AppIdHave, AppId)
+		return
+	}
+
+	random = plain[:16:16]
+	rawXMLMsg = plain[20:msgEnd]
+	return
+}