实现消息解密

util/crypto.go

@@ -0,0 +1,113 @@
+package util
+
+import (
+	"crypto/aes"
+	"crypto/cipher"
+	"encoding/base64"
+	"errors"
+	"fmt"
+)
+
+//DecryptMsg 消息解密
+func DecryptMsg(appID, encryptedMsg, aesKey string) (rawMsgXMLBytes []byte, err error) {
+	var encryptedMsgBytes, key, getAppIDBytes []byte
+	encryptedMsgBytes, err = base64.StdEncoding.DecodeString(encryptedMsg)
+	if err != nil {
+		return
+	}
+	key, err = aesKeyDecode(aesKey)
+	if err != nil {
+		return
+	}
+	_, rawMsgXMLBytes, getAppIDBytes, err = AESDecryptMsg(encryptedMsgBytes, key)
+	if err != nil {
+		err = fmt.Errorf("消息解密失败,%v", err)
+		return
+	}
+	if appID != string(getAppIDBytes) {
+		err = fmt.Errorf("消息解密校验APPID失败")
+		return
+	}
+	return
+}
+
+func aesKeyDecode(encodedAESKey string) (key []byte, err error) {
+	if len(encodedAESKey) != 43 {
+		err = errors.New("the length of encodedAESKey must be equal to 43")
+		return
+	}
+	key, err = base64.StdEncoding.DecodeString(encodedAESKey + "=")
+	if err != nil {
+		return
+	}
+	if len(key) != 32 {
+		err = errors.New("encodingAESKey invalid")
+		return
+	}
+	return
+}
+
+// AESDecryptMsg ciphertext = AES_Encrypt[random(16B) + msg_len(4B) + rawXMLMsg + appId]
+func AESDecryptMsg(ciphertext []byte, aesKey []byte) (random, rawXMLMsg, appID []byte, err error) {
+	const (
+		BlockSize = 32            // PKCS#7
+		BlockMask = BlockSize - 1 // BLOCK_SIZE 为 2^n 时, 可以用 mask 获取针对 BLOCK_SIZE 的余数
+	)
+
+	if len(ciphertext) < BlockSize {
+		err = fmt.Errorf("the length of ciphertext too short: %d", len(ciphertext))
+		return
+	}
+	if len(ciphertext)&BlockMask != 0 {
+		err = fmt.Errorf("ciphertext is not a multiple of the block size, the length is %d", len(ciphertext))
+		return
+	}
+
+	plaintext := make([]byte, len(ciphertext)) // len(plaintext) >= BLOCK_SIZE
+
+	// 解密
+	block, err := aes.NewCipher(aesKey)
+	if err != nil {
+		panic(err)
+	}
+	mode := cipher.NewCBCDecrypter(block, aesKey[:16])
+	mode.CryptBlocks(plaintext, ciphertext)
+
+	// PKCS#7 去除补位
+	amountToPad := int(plaintext[len(plaintext)-1])
+	if amountToPad < 1 || amountToPad > BlockSize {
+		err = fmt.Errorf("the amount to pad is incorrect: %d", amountToPad)
+		return
+	}
+	plaintext = plaintext[:len(plaintext)-amountToPad]
+
+	// 反拼接
+	// len(plaintext) == 16+4+len(rawXMLMsg)+len(appId)
+	if len(plaintext) <= 20 {
+		err = fmt.Errorf("plaintext too short, the length is %d", len(plaintext))
+		return
+	}
+	rawXMLMsgLen := int(decodeNetworkByteOrder(plaintext[16:20]))
+	if rawXMLMsgLen < 0 {
+		err = fmt.Errorf("incorrect msg length: %d", rawXMLMsgLen)
+		return
+	}
+	appIDOffset := 20 + rawXMLMsgLen
+	if len(plaintext) <= appIDOffset {
+		err = fmt.Errorf("msg length too large: %d", rawXMLMsgLen)
+		return
+	}
+
+	random = plaintext[:16:20]
+	rawXMLMsg = plaintext[20:appIDOffset:appIDOffset]
+	appID = plaintext[appIDOffset:]
+	return
+}
+
+// 从 4 字节的网络字节序里解析出整数
+func decodeNetworkByteOrder(orderBytes []byte) (n uint32) {
+	return uint32(orderBytes[0])<<24 |
+		uint32(orderBytes[1])<<16 |
+		uint32(orderBytes[2])<<8 |
+		uint32(orderBytes[3])
+}

util/signature.go

@@ -0,0 +1,18 @@
+package util
+
+import (
+	"crypto/sha1"
+	"fmt"
+	"io"
+	"sort"
+)
+
+//Signature sha1签名
+func Signature(params ...string) string {
+	sort.Strings(params)
+	h := sha1.New()
+	for _, s := range params {
+		io.WriteString(h, s)
+	}
+	return fmt.Sprintf("%x", h.Sum(nil))
+}