Padding is invalid and cannot be removed. Rjindaal encryption

Question

I am using same initialization vector and same key for encryption and decryption. However I am getting error saying "Padding is invalid and cannot be removed" In web application I am encrypting data and saving encrypted data inside sql server table column (nvarchar(max)). I have windows service which reads encrypted data and decrypt. Can someone please tell me where am I doing wrong.

public byte[] Encrypt(string clearText, string key, byte[] initialisationVector, int blockSizeInBits)
{//hidden logic
    rijndaelManaged.Mode = CipherMode.CBC;
    rijndaelManaged.Padding = PaddingMode.PKCS7;
//hidden logic
        return memoryStream.ToArray();

    }

calling like this

    Dim encryptionKey As String = ConfigurationManager.AppSettings("Key")
    ' Arrange - need 32 byte IV for 256-bit
    Dim cryptographer3 As ICryptographer = New Cryptographer()
    Dim initialisationVector3 As Byte() = {&H26, &HDC, &HFF, &H0, &HAD, &HED, _
        &H7A, &HEE, &HC5, &HFE, &H7, &HAF, _
        &H4D, &H8, &H22, &H3C, &H26, &HDC, _
        &HFF, &H0, &HAD, &HED, &H7A, &HEE, _
        &HC5, &HFE, &H7, &HAF, &H4D, &H8, _
        &H22, &H3C}

    ' Act
    Dim encryptedString As Byte() = cryptographer3.Encrypt(strForEncryption, encryptionKey, initialisationVector3, 256)
    'Dim decrypt3 As String = cryptographer3.Decrypt(encryptedString, Key, initialisationVector3, 256)
    Return System.Text.Encoding.Unicode.GetString(encryptedString)

decryption method

public string Decrypt(byte[] cipherText, string key, byte[] initialisationVector, int blockSizeInBits)
{
  //hidden logic
    rijndaelManaged.Mode = CipherMode.CBC;
    rijndaelManaged.Padding = PaddingMode.PKCS7;
    //hidden logic
}

callling like this

if (encryptedIdentificationValue.Trim().Length > 0)
        {
            string decryptionKey = ConfigurationManager.AppSettings["Key"];
            // Arrange - need 32 byte IV for 256-bit
            ICryptographer cryptographer3 = new Cryptographer();
            byte[] initialisationVector3 =
                {
                    0x26, 0xdc, 0xff, 0x0, 0xad, 0xed,
                    0x7a, 0xee, 0xc5, 0xfe, 0x7, 0xaf,
                    0x4d, 0x8, 0x22, 0x3c, 0x26, 0xdc,
                    0xff, 0x0, 0xad, 0xed, 0x7a, 0xee,
                    0xc5, 0xfe, 0x7, 0xaf, 0x4d, 0x8,
                    0x22, 0x3c
                };

            return cryptographer3.Decrypt(encryptedIdentificationValue, decryptionKey, initialisationVector3, 256);
        }

Answer 1

The "Padding is invalid" message can mean many different things. It might be a problem with just the padding, or it might be a problem with the whole encryption including the padding. You can take some steps to diagnose the problem.

1. Set the decryption method to expect no padding.

2. Decrypt a message. You will not get the padding error, since you aren't checking it.

3. Look at the decrypted message. If it is junk all the way through, then your problem is not padding but either encryption or decryption, usually decryption. Check that your key and IV are byte for byte the same. If the message is fine, with some extra characters at the end, then check that those extra characters match what you would expect from PKCS7 padding.

4. When you have diagnosed the problem, you must set the decryption method back to PKCS7 padding.