Question

I am encryption/decryption some plain text using following code.

private static string EncryptionKey = "@#$%^&*()2343";    
private static byte[] Salt = Encoding.ASCII.GetBytes(EncryptionKey.Length.ToString()); 

public static string EncryptIt(string Input)    
{    
    RijndaelManaged Cipher = new RijndaelManaged();    
    byte[] TextByteArray = Encoding.Unicode.GetBytes(Input);    
    PasswordDeriveBytes Key = new PasswordDeriveBytes(EncryptionKey, Salt);    

    using (ICryptoTransform Transform = Cipher.CreateEncryptor(Key.GetBytes(32), Key.GetBytes(16)))    
    {        
        using (MemoryStream MS = new MemoryStream())    
        {    
            using (CryptoStream CS = new CryptoStream(MS, Transform, CryptoStreamMode.Write))    
            {    
                CS.Write(TextByteArray, 0, TextByteArray.Length);    
                CS.FlushFinalBlock();    
                return Convert.ToBase64String(MS.ToArray());    
            }    
        }    
    }    
}    

public static string DecryptIt(string Input)    
{    
    RijndaelManaged Cipher = new RijndaelManaged();    
    byte[] EncryptedByteArray = Convert.FromBase64String(Input);    
    PasswordDeriveBytes Key = new PasswordDeriveBytes(EncryptionKey, Salt);    

    using (ICryptoTransform Transform = Cipher.CreateDecryptor(Key.GetBytes(32), Key.GetBytes(16)))    
    {    
        using (MemoryStream MS = new MemoryStream(EncryptedByteArray))    
        {    
            using (CryptoStream cryptoStream = new CryptoStream(MS, Transform, CryptoStreamMode.Read))    
            {    
                byte[] TransformedText = new byte[EncryptedByteArray.Length];    
                int Count = cryptoStream.Read(TransformedText, 0, TransformedText.Length);    
                return Encoding.Unicode.GetString(TransformedText, 0, Count);    
            }    
        }    
    }    
}    

In most of the cases, this code works fine. However in some cases when I try to decrypt the encrypted text, I get following exception when byte[] EncryptedByteArray = Convert.FromBase64String(Input) is called in DecryptIt methods.

The input is not a valid Base-64 string as it contains a non-base 64 character, more than two padding characters, or a non-white space character among the padding characters.

Any idea what could be causing this exception. What I am finding more puzzling is that why this excpetion is not thrown on every cases and only few cases.

EDIT :
Sample Input to DecryptIt method that throws exception is below. Please note that I have changed the value of EncryptionKey variable in my sample above.

oaOQ6qWWDwWby3C04N7HJAiqQgILBifqdHq4OQ5KDDRA3F2ZlBITu31a8mJJQ8sKn4g3vODFEJbigtNZozv6ockAdsDChhHwaaLL4l8MJPKbV1EiUE3rL30y+xHz/S1a8mJJQ8sKn4g3vODFEJbigtNZozv6ockAdsDChhHwaaLL4l8MJPKbV1EiUE3rL30y+oz/eR9OzXn+3Lepo0tRqH5BsfvEtJ/IcqRu3gJiIBTMAM0TmVxa2EZSj2mn6jZlgvlOEFCWzNKS3R9OzXn+In1br14venJmpApXyt930khz35UE5BtWn3Fq7jyer6mY2l60P/cI4z

Answer 1

Your sample deconverts perfectly with 2 extra ‘=’ at the end.
So somewhere they are lost in transport.

The ecrypted text is sent via email in a http link.

So that involves both URL and HTML encoding? Plenty of room for an error.

Run a test with a small string ending in ==.