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Encrypting and decrypting a string in C#

Posted on 2009-04-08
Medium Priority
Last Modified: 2012-06-27
I am trying to encrypt data stored and sent back from a windows mobile device using the encrypt function below, i couldnt access PasswordDeriveBytes SecretKey = new PasswordDeriveBytes(Password, Salt); from using the System.Security.Cryptography so i included the OpenNETCF.Security.Cryptography; instead.

However i am trying to decrypt the string back to plain text in a .net web application and i keep getting the error Padding is invalid and cannot be removed.

If i use the decrypt function on the windows mobile app(compat framework 2.) it does decrypt it back though, i guessing that it has to do with using the OpenNETCF library instead ?

Does any one know how to overcome this issue or have an alternative way to achive what im trying to do ?
public static string Encrypt(string clearText, string Password)
            RijndaelManaged RijndaelCipher = new RijndaelManaged();
            RijndaelCipher.Padding =  PaddingMode.PKCS7 ;
            byte[] PlainText = System.Text.Encoding.Unicode.GetBytes(clearText);
            byte[] Salt = Encoding.ASCII.GetBytes(Password.Length.ToString());
            PasswordDeriveBytes SecretKey = new PasswordDeriveBytes(Password, Salt);
            //Creates a symmetric encryptor object.
            ICryptoTransform Encryptor = RijndaelCipher.CreateEncryptor(SecretKey.GetBytes(32), SecretKey.GetBytes(16));
            MemoryStream memoryStream = new MemoryStream();
            //Defines a stream that links data streams to cryptographic transformations
            CryptoStream cryptoStream = new CryptoStream(memoryStream, Encryptor, CryptoStreamMode.Write);
            cryptoStream.Write(PlainText, 0, PlainText.Length);
            //Writes the final state and clears the buffer
            byte[] CipherBytes = memoryStream.ToArray();
            string EncryptedData = Convert.ToBase64String(CipherBytes);
            return EncryptedData;
        public static string Decrypt(string TextToBeDecrypted,string Password)
            RijndaelManaged RijndaelCipher = new RijndaelManaged();
            RijndaelCipher.Padding = PaddingMode.PKCS7 ;
            byte[] EncryptedData = Convert.FromBase64String(TextToBeDecrypted);
            byte[] Salt = Encoding.ASCII.GetBytes(Password.Length.ToString());
            //Making of the key for decryption
            PasswordDeriveBytes SecretKey = new PasswordDeriveBytes(Password, Salt);
            //Creates a symmetric Rijndael decryptor object.
            ICryptoTransform Decryptor = RijndaelCipher.CreateDecryptor(SecretKey.GetBytes(32), SecretKey.GetBytes(16));
            MemoryStream memoryStream = new MemoryStream(EncryptedData);
            //Defines the cryptographics stream for decryption.THe stream contains decrpted data
            CryptoStream cryptoStream = new CryptoStream(memoryStream, Decryptor, CryptoStreamMode.Read);
            byte[] PlainText = new byte[EncryptedData.Length];
            int DecryptedCount = cryptoStream.Read(PlainText, 0, PlainText.Length);
            //Converting to string
            string DecryptedData = Encoding.Unicode.GetString(PlainText, 0, DecryptedCount);
            return DecryptedData;

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Question by:MCLR
  • 2
LVL 12

Expert Comment

ID: 24108445
This looks like it should help:  http://dalelane.co.uk/blog/?p=234

Author Comment

ID: 24108623
thanks, but i have similar code already, in that the only difference between the function on the mobile device and the .net app  is that I use:
OpenNETCF.Security.Cryptography.PasswordDeriveBytes instead of

but yet i am getting the error error Padding is invalid and cannot be removed.

Accepted Solution

MCLR earned 0 total points
ID: 24139549
I couldnt get that method to work after so in teh end i used the following
key = Encoding.UTF8.GetBytes(stringKey.Substring(0, 8));
DESCryptoServiceProvider des = new DESCryptoServiceProvider();
Byte[] byteArray = Encoding.UTF8.GetBytes(text);
MemoryStream memoryStream = new MemoryStream();
CryptoStream cryptoStream = new CryptoStream(memoryStream,
des.CreateEncryptor(key, IV), CryptoStreamMode.Write);
cryptoStream.Write(byteArray, 0, byteArray.Length);
return Convert.ToBase64String(memoryStream.ToArray());

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