使用“AesManaged”C# 解密字符串时，填充无效且无法删除异常

Question

请建议我在哪里需要更新/重构代码以消除异常。当我尝试使用以下代码解密加密字符串时遇到异常。

下面一行是抛出异常

using (StreamReader srDecrypt = new StreamReader(csDecrypt))
{
     // Read the decrypted bytes from the decrypting stream
     // and place them in a string.
     plaintext = srDecrypt.ReadToEnd();
}

public string EncryptAuthenticationTokenAes(string plainText)
{

    byte[] encrypted;
    // Create an AesManaged object
    // with the specified key and IV.
    using (AesManaged aesAlg = new AesManaged())
    {

        // Create a decrytor to perform the stream transform.
        ICryptoTransform encryptor = aesAlg.CreateEncryptor(aesAlg.Key, aesAlg.IV);
        aesAlg.Padding = PaddingMode.None;
        // Create the streams used for encryption.
        using (MemoryStream msEncrypt = new MemoryStream())
        {
            using (CryptoStream csEncrypt = new CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write))
            {
                using (StreamWriter swEncrypt = new StreamWriter(csEncrypt))
                {

                    //Write all data to the stream.
                    swEncrypt.Write(plainText);
                }
                encrypted = msEncrypt.ToArray();
            }
        }
    }


    // Return the encrypted bytes from the memory stream.
    return Convert.ToBase64String(encrypted);

}

public string DecryptPasswordAes(string encryptedString)
{
    //Convert cipher text back to byte array
    byte[] cipherText = Convert.FromBase64String(encryptedString);

    // Declare the string used to hold
    // the decrypted text.
    string plaintext = null;

    // Create an AesManaged object
    // with the specified key and IV.
    using (AesManaged aesAlg = new AesManaged())
    {
        // Create a decrytor to perform the stream transform.
        ICryptoTransform decryptor = aesAlg.CreateDecryptor(aesAlg.Key, aesAlg.IV);
        aesAlg.Padding = PaddingMode.None;
        // Create the streams used for decryption.
        using (MemoryStream msDecrypt = new MemoryStream(cipherText))
        {
            using (CryptoStream csDecrypt = new CryptoStream(msDecrypt, decryptor, CryptoStreamMode.Read))
            {
                using (StreamReader srDecrypt = new StreamReader(csDecrypt))
                {

                    // Read the decrypted bytes from the decrypting stream
                    // and place them in a string.
                    plaintext = srDecrypt.ReadToEnd();
                }
            }
        }

    }

    return plaintext;

}

Answer 1

使用 CryptoStream 时的标准错误，您忘记强制它加密流的最后一个字节。它将字节保存在内部缓冲区中，直到有足够的字节到达以发出块。您必须强制输出最后几个字节。修复：

    using (var msEncrypt = new MemoryStream())
    using (var csEncrypt = new CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write))
    using (var swEncrypt = new StreamWriter(csEncrypt)) {
        swEncrypt.Write(plainText);
        csEncrypt.FlushFinalBlock();
        encrypted = msEncrypt.ToArray();
    }

解密时出现异常，因为 encrypted 缺少最终填充。真正的问题是由 using 语句引起的，如果您等到 CryptoStream 关​​闭后才获取加密字节，则不会出现此问题。但这并不能很好地工作，因为 StreamWriter 上的 using 语句也会关闭 CryptoStream 和 MemoryStream。显式使用 FlushFinalBlock() 是最好的解决方法。