C#中Rijndael解密仅返回16字符问题的修复方案咨询

问题描述 #

使用当前Rijndael加密解密方法时，加密16个字符以上的字符串后解密，结果最多仅返回16个字符。例如输入"ABCDEFGHIJKLMNOP12345678"，解密后输出为"ABCDEFGHIJKLMNOP"。当前参数配置：hashAlgorithm="SHA1"，passwordIterations=2，keySize=256。

问题原因 #

解密方法中仅调用了一次cryptoStream.Read()，而CryptoStream.Read()无法保证一次性读取所有解密后的数据——Rijndael默认块大小为128位（16字节），单次读取仅会返回第一个块的内容，后续数据直接丢失。

修复后的代码 #

public class RijndaelSimple
{
    public static string Encrypt(string plainText,
                                 string passPhrase,
                                 string saltValue,
                                 string hashAlgorithm,
                                 int passwordIterations,
                                 string initVector,
                                 int keySize)
    {
        byte[] initVectorBytes = Encoding.ASCII.GetBytes(initVector);
        byte[] saltValueBytes = Encoding.ASCII.GetBytes(saltValue);
        
        byte[] plainTextBytes = Encoding.UTF8.GetBytes(plainText);

        PasswordDeriveBytes password = new PasswordDeriveBytes(
            passPhrase, saltValueBytes, hashAlgorithm, passwordIterations);

        byte[] keyBytes = password.GetBytes(keySize / 8);

        RijndaelManaged symmetricKey = new RijndaelManaged();
        symmetricKey.Mode = CipherMode.CBC;

        ICryptoTransform encryptor = symmetricKey.CreateEncryptor(keyBytes, initVectorBytes);

        using (MemoryStream memoryStream = new MemoryStream())
        using (CryptoStream cryptoStream = new CryptoStream(memoryStream, encryptor, CryptoStreamMode.Write))
        {
            cryptoStream.Write(plainTextBytes, 0, plainTextBytes.Length);
            cryptoStream.FlushFinalBlock();
            byte[] cipherTextBytes = memoryStream.ToArray();
            return Convert.ToBase64String(cipherTextBytes);
        }
    }

    public static string Decrypt(string cipherText,
        string passPhrase,
        string saltValue,
        string hashAlgorithm,
        int passwordIterations,
        string initVector,
        int keySize)
    {
        byte[] initVectorBytes = Encoding.ASCII.GetBytes(initVector);
        byte[] saltValueBytes = Encoding.ASCII.GetBytes(saltValue);

        byte[] cipherTextBytes = Convert.FromBase64String(cipherText);

        PasswordDeriveBytes password = new PasswordDeriveBytes(
            passPhrase, saltValueBytes, hashAlgorithm, passwordIterations);

        byte[] keyBytes = password.GetBytes(keySize / 8);

        RijndaelManaged symmetricKey = new RijndaelManaged();
        symmetricKey.Mode = CipherMode.CBC;

        ICryptoTransform decryptor = symmetricKey.CreateDecryptor(keyBytes, initVectorBytes);

        using (MemoryStream memoryStream = new MemoryStream(cipherTextBytes))
        using (CryptoStream cryptoStream = new CryptoStream(memoryStream, decryptor, CryptoStreamMode.Read))
        using (MemoryStream plainTextStream = new MemoryStream())
        {
            byte[] buffer = new byte[4096]; // 用4KB缓冲区分批读取数据
            int bytesRead;
            while ((bytesRead = cryptoStream.Read(buffer, 0, buffer.Length)) > 0)
            {
                plainTextStream.Write(buffer, 0, bytesRead);
            }
            return Encoding.UTF8.GetString(plainTextStream.ToArray());
        }
    }
}

关键修改说明 #

• 解密逻辑优化：将单次Read操作改为循环读取，直到Read返回0（无更多数据），确保所有解密后的内容都被读取。
• 资源自动管理：使用using语句替代手动调用Close()，自动释放流资源，避免泄漏。
• 缓冲区效率提升：采用4KB大小的缓冲区分批处理数据，更适合长字符串的读写操作。

内容的提问来源于stack exchange，提问作者nicedev92