步骤三：接收回调

import hashlib
bytes_b1 = (timestamp + nonce + encrypt_key).encode('utf-8')
bytes_b = bytes_b1 + body
h = hashlib.sha256(bytes_b)
signature = h.hexdigest()

# check if request headers['X-Lark-Signature'] equals to signature

import org.apache.commons.codec.binary.Hex;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
class Main {
  public String calculateSignature(String timestamp, String nonce, String encryptKey, String bodyString) throws NoSuchAlgorithmException {
	  StringBuilder content = new StringBuilder();
	  content.append(timestamp).append(nonce).append(encryptKey).append(bodyString);
	  MessageDigest alg = MessageDigest.getInstance("SHA-256");
	  String sign = Hex.encodeHexString(alg.digest(content.toString().getBytes()));
	  return sign;
  }
}

import (
   "crypto/sha256"
   "fmt"
)
func calculateSignature(timestamp, nonce, encryptKey, bodystring string) string {
   var b strings.Builder
   b.WriteString(timestamp)
   b.WriteString(nonce)
   b.WriteString(encryptKey)
   b.WriteString(bodystring) //bodystring 指整个请求体，不要在反序列化后再计算
   bs := []byte(b.String())
   h := sha256.New()
   h.Write(bs)
   bs = h.Sum(nil)
   sig := fmt.Sprintf("%x", bs)
   return sig
}

var crypto = require('crypto');
function calculateSignature(timestamp, nonce, encryptKey, body) {
		const content = timestamp + nonce + encryptKey + body
		const sign = crypto.createHash('sha256').update(content).digest('hex');
		return sign
}

using System.Security.Cryptography;
public static string calculateSignature(string timestamp, string nonce, string encryptKey, string body) {
		StringBuilder content = new StringBuilder();
		content.Append(timestamp);
		content.Append(nonce);
		content.Append(encryptKey);
		content.Append(body);
		SHA256 sha256 = new SHA256CryptoServiceProvider();  
		byte[] bytes_out = sha256.ComputeHash(Encoding.UTF8.GetBytes(content.ToString()));  
		string result = BitConverter.ToString(bytes_out);  
		result = result.Replace("-", "");  
		return result;  
}

<?php
$encrypt_key = "";  // 开放平台后台的 Encrypt Key
$timestamp = "";
$nonce = "";
$body = ""; // 指整个请求体，不要在反序列化后再计算
$signature = hash("sha256", $timestamp . $nonce . $encrypt_key . $body);
// check if request headers['X-Lark-Signature'] equals to signature

import hashlib
import base64
from Crypto.Cipher import AES
class  AESCipher(object):
    def __init__(self, key):
        self.bs = AES.block_size
        self.key=hashlib.sha256(AESCipher.str_to_bytes(key)).digest()
    @staticmethod
    def str_to_bytes(data):
        u_type = type(b"".decode('utf8'))
        if isinstance(data, u_type):
            return data.encode('utf8')
        return data
    @staticmethod
    def _unpad(s):
        return s[:-ord(s[len(s) - 1:])]
    def decrypt(self, enc):
        iv = enc[:AES.block_size]
        cipher = AES.new(self.key, AES.MODE_CBC, iv)
        return  self._unpad(cipher.decrypt(enc[AES.block_size:]))
    def decrypt_string(self, enc):
        enc = base64.b64decode(enc)
        return  self.decrypt(enc).decode('utf8')
encrypt = "P37w+VZImNgPEO1RBhJ6RtKl7n6zymIbEG1pReEzghk="
cipher = AESCipher("test key")
print("明文:\n{}".format(cipher.decrypt_string(encrypt)))

package com.larksuite.oapi.sample;
import javax.crypto.Cipher;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;
import java.nio.charset.StandardCharsets;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.Base64;
public class Decrypt {
    public static void main(String[] args) throws Exception {
        Decrypt d = new Decrypt("test key");
        System.out.println(d.decrypt("P37w+VZImNgPEO1RBhJ6RtKl7n6zymIbEG1pReEzghk=")); //hello world
    }
    private byte[] keyBs;
    public Decrypt(String key) {
        MessageDigest digest = null;
        try {
            digest = MessageDigest.getInstance("SHA-256");
        } catch (NoSuchAlgorithmException e) {
            // won't happen
        }
        keyBs = digest.digest(key.getBytes(StandardCharsets.UTF_8));
    }
    public String decrypt(String base64) throws Exception {
        byte[] decode = Base64.getDecoder().decode(base64);
        Cipher cipher = Cipher.getInstance("AES/CBC/NOPADDING");
        byte[] iv = new byte[16];
        System.arraycopy(decode, 0, iv, 0, 16);
        byte[] data = new byte[decode.length - 16];
        System.arraycopy(decode, 16, data, 0, data.length);
        cipher.init(Cipher.DECRYPT_MODE, new SecretKeySpec(keyBs, "AES"), new IvParameterSpec(iv));
        byte[] r = cipher.doFinal(data);
        if (r.length > 0) {
            int p = r.length - 1;
            for (; p >= 0 && r[p] <= 16; p--) {
            }
            if (p != r.length - 1) {
                byte[] rr = new byte[p + 1];
                System.arraycopy(r, 0, rr, 0, p + 1);
                r = rr;
            }
        }
        return new String(r, StandardCharsets.UTF_8);
    }
}

package main
import (
        "crypto/aes"
        "crypto/cipher"
        "crypto/sha256"
        "encoding/base64"
        "errors"
        "fmt"
        "strings"
)
func main() {
        s, err := Decrypt("P37w+VZImNgPEO1RBhJ6RtKl7n6zymIbEG1pReEzghk=", "test key")
        if err != nil {
                panic(err)
        }
        fmt.Println(s) //hello world
}
func Decrypt(encrypt string, key string) (string, error) {
        buf, err := base64.StdEncoding.DecodeString(encrypt)
        if err != nil {
                return "", fmt.Errorf("base64StdEncode Error[%v]", err)
        }
        if len(buf) < aes.BlockSize {
                return "", errors.New("cipher  too short")
        }
        keyBs := sha256.Sum256([]byte(key))
        block, err := aes.NewCipher(keyBs[:sha256.Size])
        if err != nil {
                return "", fmt.Errorf("AESNewCipher Error[%v]", err)
        }
        iv := buf[:aes.BlockSize]
        buf = buf[aes.BlockSize:]
        // CBC mode always works in whole blocks.
        if len(buf)%aes.BlockSize != 0 {
                return "", errors.New("ciphertext is not a multiple of the block size")
        }
        mode := cipher.NewCBCDecrypter(block, iv)
        mode.CryptBlocks(buf, buf)
        n := strings.Index(string(buf), "{")
        if n == -1 {
                n = 0
        }
        m := strings.LastIndex(string(buf), "}")
        if m == -1 {
                m = len(buf) - 1
        }
        return string(buf[n : m+1]), nil
}

using System;
using System.Linq;
using System.Security.Cryptography;
using System.Text;
namespace decrypt
{
        class AESCipher
        {
                const int BlockSize = 16;
                private byte[] key;
                public AESCipher(string key)
                {
                        this.key = SHA256Hash(key);
                }
                public string DecryptString(string enc)
                {
                        byte[] encBytes = Convert.FromBase64String(enc);
                        RijndaelManaged rijndaelManaged = new RijndaelManaged();
                        rijndaelManaged.Key = this.key;
                        rijndaelManaged.Mode = CipherMode.CBC;
                        rijndaelManaged.IV = encBytes.Take(BlockSize).ToArray();
                        ICryptoTransform transform = rijndaelManaged.CreateDecryptor();
                        byte[] blockBytes = transform.TransformFinalBlock(encBytes, BlockSize, encBytes.Length - BlockSize);
                        return System.Text.Encoding.UTF8.GetString(blockBytes);
                }
                public static byte[] SHA256Hash(string str)
                {
                        byte[] bytes = Encoding.UTF8.GetBytes(str);
                        SHA256 shaManaged = new SHA256Managed();
                        return shaManaged.ComputeHash(bytes);
                }
                public static void Main(string[] args)
                {
                        string encrypt = "P37w+VZImNgPEO1RBhJ6RtKl7n6zymIbEG1pReEzghk=";
                        AESCipher cipher = new AESCipher("test key");
                        Console.WriteLine(cipher.DecryptString(encrypt));
                }
        }
}

<?php
$encrypt_data = ""; // 待解密的信息
$encrypt_key = ""; // 从开发者后台获取 Encrypt Key
$base64_decode_message = base64_decode($encrypt_data);
$iv = substr($base64_decode_message, 0, 16);
$encrypted_event = substr($base64_decode_message, 16);
$decrypt = openssl_decrypt($encrypted_event, 'AES-256-CBC', hash('sha256', $encrypt_key, true), OPENSSL_RAW_DATA, $iv);
print($decrypt); 
// get the real event