c# - AesCryptoServiceProviderを使用して誤った復号化値を取得する

Answer 1

It is easy to make implementation mistakes with cryptographic primitives, people do it all the time, it's best to use a high level library if you can.

I have a snippet that I try to keep reviewed and up to date, that works pretty close to what you're doing. It also does authentication on the cipher text, which I would recommend if there is anyway an adversary could send chosen ciphertext to your decryption implementation, there are a lot of side channel attacks related to modifying the ciphertext.

However, the problem you're having does not have any thing to do with padding, if your ciphertext doesn't matchup to your key and iv, and you didn't authenticate your iv and ciphertext, you'll typically get a padding error (if this is bubbled up a client it's called a padding oracle). You need to change your main statement to:

    string valid128BitString = "AAECAwQFBgcICQoLDA0ODw==";
    string inputValue = "Test";
    string keyValue = valid128BitString;


    byte[] byteValForString = Encoding.UTF8.GetBytes(inputValue);
    EncryptResult result = Aes128Utility.EncryptData(byteValForString, keyValue);
    EncryptResult encyptedValue = new EncryptResult();
    encyptedValue.IV = result.IV; //<--Very Important
    encyptedValue.EncryptedMsg = result.EncryptedMsg;

    string finalResult =Encoding.UTF8.GetString(Aes128Utility.DecryptData(encyptedValue, keyValue));

So you use the same IV to decrypt as you did to encrypt.