How to Fix 'Padding is invalid and cannot be removed' Exception in Rijndael XML Decryption?

Invalid padding exception in XmlDocument encryption

When decrypting XmlDocument using Rijndael algorithm, you may encounter the exception "Padding is invalid and cannot be removed". This means that the Data Encryption Standard (DES) used in Rijndael encryption is incompatible with the padding applied when decrypting.

To resolve this issue, it is important to ensure that both encryption and decryption operations use the same padding algorithm. The problem arises because Rijndael (aka AES) is a block cipher that operates in fixed 128-bit blocks.

Encrypted data for padding to ensure the last block always has the correct dimensions. You can resolve padding mismatch issues by explicitly setting padding for encryption and decryption. Unless there are special requirements for a specific padding method, it is recommended to use industry standard PKCS#7 padding.

Here is a modified version of the code where the padding is set explicitly:

<code class="language-csharp">public void Cryptography(XmlDocument doc, bool cryptographyMode)
{
    using (RijndaelManaged key = new RijndaelManaged())
    {
        key.Padding = PaddingMode.PKCS7;  // 显式设置 AES 128 填充模式

        // ...  您的现有代码（需要进行必要的调整以设置填充）...

        if (cryptographyMode)
        {
            Encrypt(doc, "Content", key);
        }
        else
        {
            Decrypt(doc, key);
        }
    }
    // ...
}</code>

Ensure that the using object is released correctly by using the RijndaelManaged statement to avoid resource leaks. Note that you will need to adapt the Encrypt and Decrypt methods to your existing code to properly handle PKCS#7 padding. This usually involves making corresponding modifications to the inputs and outputs of the encryption and decryption functions.

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