错误AES-标准SymmetricAlgorithm，“填充无效且无法删除”

Question

I am using AES - Standard SymmetricAlgorithm, for Encrypting and Decrypting string. String is encrypting successfully but when it comes to decrypt the compiler gives me the exception ie

“Padding is invalid and cannot be removed”.

I have created a demo console application for testing, please have a look on below code.

The Main Method:

static void Main(string[] args)
{
    var content = "5466160057107706";
    var key = "E546C8DF278CD5931069B522E695D4F2";

    var encrypted = EncryptString(content, key);
    Console.WriteLine(encrypted);
    var decrypted = DecryptString(encrypted, key);
    Console.WriteLine(decrypted);
    Console.ReadLine();
}

Method added for Encryption:

public static string EncryptString(string text, string keyString)
{
    var key = Encoding.UTF8.GetBytes(keyString);
    using (var aesAlg = Aes.Create())
    {
        using (var encryptor = aesAlg.CreateEncryptor(key, aesAlg.IV))
        {
            using (var msEncrypt = new MemoryStream())
            {
                using (var csEncrypt = new CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write))
                using (var swEncrypt = new StreamWriter(csEncrypt))
                {
                    swEncrypt.Write(text);
                }
                var iv = aesAlg.IV;
                var decryptedContent = msEncrypt.ToArray();
                var result = new byte[iv.Length + decryptedContent.Length];
                Buffer.BlockCopy(iv, 0, result, 0, iv.Length);
                Buffer.BlockCopy(decryptedContent, 0, result, iv.Length, decryptedContent.Length);
                return Convert.ToBase64String(result);
            }
        }
    }
}

Method added for Decryption:

public static string DecryptString(string cipherText, string keyString)
{
    var fullCipher = Convert.FromBase64String(cipherText);
    var iv = new byte[16];
    var cipher = new byte[16];
    Buffer.BlockCopy(fullCipher, 0, iv, 0, iv.Length);
    Buffer.BlockCopy(fullCipher, iv.Length, cipher, 0, iv.Length);
    var key = Encoding.UTF8.GetBytes(keyString);
    using (var aesAlg = Aes.Create())
    {
        using (var decryptor = aesAlg.CreateDecryptor(key, iv))
        {
            string result;
            using (var msDecrypt = new MemoryStream(cipher))
            {
                using (var csDecrypt = new CryptoStream(msDecrypt, decryptor, CryptoStreamMode.Read))
                {
                    using (var srDecrypt = new StreamReader(csDecrypt))
                    {
                        result = srDecrypt.ReadToEnd();
                    }
                }
            }
            return result;
        }
    }
}

Here is the Error Snap which occurs in the DecryptString() method:

Any advice, how to solve this issue?

Answer 1

Clue: var cipher = new byte[16];

Why are you assuming your cipher would be ONLY 16 bytes ? What if it is more than this ?

In fact, if I run this program and debug, I see that your cipher is 32 bytes.

So, the following 2 line changes makes it work:

var cipher = new byte[32];

Buffer.BlockCopy(fullCipher, iv.Length, cipher, 0, cipher.Length);

In any case, you would need to dynamically determine your size of cipher.