Invalid length for a Base-64 char array.

Question

As the title says, I am getting:

Invalid length for a Base-64 char array.

I have read about this problem on here and it seems that the suggestion is to store ViewState in SQL if it is large. I am using a wizard with a good deal of data collection so chances are my ViewSate is large. But, before I turn to the "store-in-DB" solution, maybe somebody can take a look and tell me if I have other options?

I construct the email for delivery using the below method:

public void SendEmailAddressVerificationEmail(string userName, string to)
        {
            string msg = "Please click on the link below or paste it into a browser to verify your email account.<BR><BR>" +
                            "<a href=\"" + _configuration.RootURL + "Accounts/VerifyEmail.aspx?a=" +
                            userName.Encrypt("verify") + "\">" +
                            _configuration.RootURL + "Accounts/VerifyEmail.aspx?a=" +
                            userName.Encrypt("verify") + "</a>";

            SendEmail(to, "", "", "Account created! Email verification required.", msg);
        }

The Encrypt method looks like this:

public static string Encrypt(string clearText, string Password)
        {

            byte[] clearBytes = System.Text.Encoding.Unicode.GetBytes(clearText);

            PasswordDeriveBytes pdb = new PasswordDeriveBytes(Password, new byte[] { 0x49, 0x76, 0x61, 0x6e, 0x20, 0x4d, 0x65, 0x64, 0x76, 0x65, 0x64, 0x65, 0x76 });


            byte[] encryptedData = Encrypt(clearBytes, pdb.GetBytes(32), pdb.GetBytes(16));

            return Convert.ToBase64String(encryptedData);
        }

Here is what the HTML looks like in hotmail:

Please click on the link below or paste it into a browser to verify your email account.

http://localhost:1563/Accounts/VerifyEmail.aspx?a=YOHY57xYRENEOu3H+FGq1Rf09AZAI56EPjfwuK8XWKg=

On the receiving end, the VerifyEmail.aspx.cs page has the line:

 string username = Cryptography.Decrypt(_webContext.UserNameToVerify, "verify");

Here is the getter for UserNameToVerify:

public string UserNameToVerify
        {
            get
            {
                return GetQueryStringValue("a").ToString();
            }
        }

And here is the GetQueryStringValue method:

private static string GetQueryStringValue(string key)
        {
            return HttpContext.Current.Request.QueryString.Get(key);
        }

And the decrypt method looks like:

 public static string Decrypt(string cipherText, string password)
        {

            **// THE ERROR IS THROWN HERE!!**
            byte[] cipherBytes = Convert.FromBase64String(cipherText);

Can this error be remedied with a code fix or must I store ViewState in the database?

Thanks in advance.

Answer 1

My initial guess without knowing the data would be that the UserNameToVerify is not a multiple of 4 in length. Check out the FromBase64String on msdn.

     // Ok
     byte[] b1 = Convert.FromBase64String("CoolDude");
     // Exception
     byte[] b2 = Convert.FromBase64String("MyMan");

Answer 2

My guess is that you simply need to URL-encode your Base64 string when you include it in the querystring.

Base64 encoding uses some characters which must be encoded if they're part of a querystring (namely + and /, and maybe = too). If the string isn't correctly encoded then you won't be able to decode it successfully at the other end, hence the errors.

You can use the HttpUtility.UrlEncode method to encode your Base64 string:

string msg = "Please click on the link below or paste it into a browser "
             + "to verify your email account.<br /><br /><a href=\""
             + _configuration.RootURL + "Accounts/VerifyEmail.aspx?a="
             + HttpUtility.UrlEncode(userName.Encrypt("verify")) + "\">"
             + _configuration.RootURL + "Accounts/VerifyEmail.aspx?a="
             + HttpUtility.UrlEncode(userName.Encrypt("verify")) + "</a>";

Answer 3

The length of a base64 encoded string is always a multiple of 4. If it is not a multiple of 4, then = characters are appended until it is. A query string of the form ?name=value has problems when the value contains = charaters (some of them will be dropped, I don't recall the exact behavior). You may be able to get away with appending the right number of = characters before doing the base64 decode.

Edit 1

You may find that the value of UserNameToVerify has had "+"'s changed to " "'s so you may need to do something like so;

a = a.Replace(" ","+");

This should get the length right;

int mod4 = a.Length % 4;
if ( mod4 > 0 )
{
    a += new string( '=', 4 - mod4 );
}

Of course calling UrlEncode (as in LukeH's answer) should make this all moot.

Answer 4

Hello,

Just wanted to say thanks to Uncle Brad and LukeH. I had some problems generating a preview image from a FileUpload control, I kept getting the "Invalid length for a Base-64 char array" error when trying to convert my base 64 string to a byte array.

Both HttpUtility.UrlEncode and string.Replace(" ","+") worked brilliantly, cheers!