要在C#和Node.js中互相实现DES加密和解密，可以使用相同的算法和密钥来进行操作。下面是一个示例：

C#中的DES加密解密示例：

using System;
using System.Security.Cryptography;
using System.Text;

public class Program
{
    public static void Main()
    {
        string originalText = "Hello, world!";
        string key = "mySecretKey";

        byte[] encryptedBytes = Encrypt(originalText, key);
        string encryptedText = Convert.ToBase64String(encryptedBytes);
        Console.WriteLine("Encrypted text: " + encryptedText);

        string decryptedText = Decrypt(encryptedBytes, key);
        Console.WriteLine("Decrypted text: " + decryptedText);
    }

    public static byte[] Encrypt(string plainText, string key)
    {
        byte[] keyBytes = Encoding.UTF8.GetBytes(key);
        byte[] plainBytes = Encoding.UTF8.GetBytes(plainText);

        using (DESCryptoServiceProvider des = new DESCryptoServiceProvider())
        {
            des.Key = keyBytes;
            des.IV = keyBytes;

            using (MemoryStream memoryStream = new MemoryStream())
            {
                using (CryptoStream cryptoStream = new CryptoStream(memoryStream, des.CreateEncryptor(), CryptoStreamMode.Write))
                {
                    cryptoStream.Write(plainBytes, 0, plainBytes.Length);
                    cryptoStream.FlushFinalBlock();
                    return memoryStream.ToArray();
                }
            }
        }
    }

    public static string Decrypt(byte[] encryptedBytes, string key)
    {
        byte[] keyBytes = Encoding.UTF8.GetBytes(key);

        using (DESCryptoServiceProvider des = new DESCryptoServiceProvider())
        {
            des.Key = keyBytes;
            des.IV = keyBytes;

            using (MemoryStream memoryStream = new MemoryStream())
            {
                using (CryptoStream cryptoStream = new CryptoStream(memoryStream, des.CreateDecryptor(), CryptoStreamMode.Write))
                {
                    cryptoStream.Write(encryptedBytes, 0, encryptedBytes.Length);
                    cryptoStream.FlushFinalBlock();
                    return Encoding.UTF8.GetString(memoryStream.ToArray());
                }
            }
        }
    }
}

Node.js中的DES加密解密示例：

const crypto = require('crypto');

function encrypt(plainText, key) {
  const cipher = crypto.createCipheriv('des', key, key);
  let encrypted = cipher.update(plainText, 'utf8', 'base64');
  encrypted += cipher.final('base64');
  return encrypted;
}

function decrypt(encryptedText, key) {
  const decipher = crypto.createDecipheriv('des', key, key);
  let decrypted = decipher.update(encryptedText, 'base64', 'utf8');
  decrypted += decipher.final('utf8');
  return decrypted;
}

const originalText = 'Hello, world!';
const key = 'mySecretKey';

const encryptedText = encrypt(originalText, key);
console.log('Encrypted text:', encryptedText);

const decryptedText = decrypt(encryptedText, key);
console.log('Decrypted text:', decryptedText);

请注意，这只是一个基本的示例，用于演示如何在C#和Node.js中使用DES算法进行加密和解密。在实际应用中，应考虑更多的安全性和最佳实践，例如密钥管理、加密模式和填充方式的选择等。

希望以上解答对你有帮助。如果你有任何其他问题，请随时提问。

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