From 6ec06c28130bc2fc6364596048162604496ec0c7 Mon Sep 17 00:00:00 2001
From: "david.yan" <david.yan@qq.com>
Date: Sun, 6 Apr 2025 13:42:44 +0800
Subject: [PATCH] add third

---
 third/wechat.go | 65 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 65 insertions(+)
 create mode 100644 third/wechat.go

diff --git a/third/wechat.go b/third/wechat.go
new file mode 100644
index 0000000..3357e66
--- /dev/null
+++ b/third/wechat.go
@@ -0,0 +1,65 @@
+package third
+
+import (
+	"crypto/aes"
+	"crypto/cipher"
+	"encoding/base64"
+	"errors"
+)
+
+func WeChat_Decrypt(sessionKey, encryptedData, iv string) (string, error) {
+	aesKey, err := base64.StdEncoding.DecodeString(sessionKey)
+	if err != nil {
+		return "", err
+	}
+	cipherText, err := base64.StdEncoding.DecodeString(encryptedData)
+	if err != nil {
+		return "", err
+	}
+	ivBytes, err := base64.StdEncoding.DecodeString(iv)
+	if err != nil {
+		return "", err
+	}
+	block, err := aes.NewCipher(aesKey)
+	if err != nil {
+		return "", err
+	}
+	mode := cipher.NewCBCDecrypter(block, ivBytes)
+	mode.CryptBlocks(cipherText, cipherText)
+	cipherText, err = WeChat_Pkcs7Unpad(cipherText, block.BlockSize())
+	if err != nil {
+		return "", err
+	}
+
+	return string(cipherText), nil
+}
+
+// pkcs7Unpad returns slice of the original data without padding
+func WeChat_Pkcs7Unpad(data []byte, blockSize int) ([]byte, error) {
+	var (
+		// ErrInvalidBlockSize block size不合法
+		ErrInvalidBlockSize = errors.New("invalid block size")
+		// ErrInvalidPKCS7Data PKCS7数据不合法
+		ErrInvalidPKCS7Data = errors.New("invalid PKCS7 data")
+		// ErrInvalidPKCS7Padding 输入padding失败
+		ErrInvalidPKCS7Padding = errors.New("invalid padding on input")
+	)
+
+	if blockSize <= 0 {
+		return nil, ErrInvalidBlockSize
+	}
+	if len(data)%blockSize != 0 || len(data) == 0 {
+		return nil, ErrInvalidPKCS7Data
+	}
+	c := data[len(data)-1]
+	n := int(c)
+	if n == 0 || n > len(data) {
+		return nil, ErrInvalidPKCS7Padding
+	}
+	for i := 0; i < n; i++ {
+		if data[len(data)-n+i] != c {
+			return nil, ErrInvalidPKCS7Padding
+		}
+	}
+	return data[:len(data)-n], nil
+}