Problem to length of decrypted value

[HuaMin Chen]

Hi,
How to avoid THIS PROBLEM

Invalid length for a Base-64 char array or string.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.FormatException: Invalid length for a Base-64 char array or string.

Source Error:


An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.

Stack Trace:



[FormatException: Invalid length for a Base-64 char array or string.]
System.Convert.FromBase64_Decode(Char* startInputPtr, Int32 inputLength, Byte* startDestPtr, Int32 destLength) +14116343
System.Convert.FromBase64CharPtr(Char* inputPtr, Int32 inputLength) +162
System.Convert.FromBase64String(String s) +56
ChgPass._Default.DecryptStringAES(String cipherText, String sharedSecret) +231
ChgPass._Default.Page_Load(Object sender, EventArgs e) +269
System.Web.UI.Control.LoadRecursive() +71
System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +3178



due to 1st line below?

Session["userpass"] = DecryptStringAES(Request.QueryString["password"], "abcdef");

public static string DecryptStringAES(string cipherText, string sharedSecret)
{
if (string.IsNullOrEmpty(cipherText))
throw new ArgumentNullException("cipherText");
if (string.IsNullOrEmpty(sharedSecret))
throw new ArgumentNullException("sharedSecret");

// Declare the RijndaelManaged object
// used to decrypt the data.
RijndaelManaged aesAlg = null;

// Declare the string used to hold
// the decrypted text.
string plaintext = null;

try
{
// generate the key from the shared secret and the salt
Rfc2898DeriveBytes key = new Rfc2898DeriveBytes(sharedSecret, _salt);

// Create the streams used for decryption.
byte[] bytes = Convert.FromBase64String(cipherText);
using (MemoryStream msDecrypt = new MemoryStream(bytes))
{
// Create a RijndaelManaged object
// with the specified key and IV.
aesAlg = new RijndaelManaged();
aesAlg.Key = key.GetBytes(aesAlg.KeySize / 8);
// Get the initialization vector from the encrypted stream
aesAlg.IV = ReadByteArray(msDecrypt);
// Create a decrytor to perform the stream transform.
ICryptoTransform decryptor = aesAlg.CreateDecryptor(aesAlg.Key, aesAlg.IV);
using (CryptoStream csDecrypt = new CryptoStream(msDecrypt, decryptor, CryptoStreamMode.Read))
{
using (StreamReader srDecrypt = new StreamReader(csDecrypt))

// Read the decrypted bytes from the decrypting stream
// and place them in a string.
plaintext = srDecrypt.ReadToEnd();
}
}
}
finally
{
// Clear the RijndaelManaged object.
if (aesAlg != null)
aesAlg.Clear();
}

return plaintext;
}



Many Thanks & Best Regards, Hua Min

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