Bad Data: Cryptography C#

Question

I am new to C# and cryptography and I've made up the below code by picking up data from various sources like CodeProject and StackOverflow.

public class CryptoSafe
{
    private const int SaltSize = 8;

    public void EncryptAndWrite(FileInfo targetFile, string password)
    {
        FileStream stream = new FileStream(targetFile.FullName, FileMode.Open, FileAccess.Write);

        DESCryptoServiceProvider cryptic = new DESCryptoServiceProvider();
        // 
        var keyGenerator = new Rfc2898DeriveBytes(password, SaltSize);
        var rijndael = Rijndael.Create();
        var length = rijndael.BlockSize;

        // BlockSize, KeySize in bit --> divide by 8
        cryptic.IV = keyGenerator.GetBytes(rijndael.BlockSize / 16);
        cryptic.Key = keyGenerator.GetBytes(rijndael.KeySize / 32);

        CryptoStream crStream = new CryptoStream(stream, cryptic.CreateEncryptor(), CryptoStreamMode.Write);
        byte[] data = ASCIIEncoding.ASCII.GetBytes(System.DateTime.Now.ToString("dd-MMM-yyyy HH;mm:ss"));

        crStream.Write(data, 0, data.Length);

        crStream.Close();
        stream.Close();
    }



    public string DecryptAndRead(FileInfo sourceFile, string password)
    {
        FileStream stream = new FileStream(sourceFile.FullName, FileMode.Open, FileAccess.Read);
        DESCryptoServiceProvider cryptic = new DESCryptoServiceProvider();
        // read salt
        //var fileStream = sourceFile.OpenRead();
        //var salt = new byte[SaltSize];
        // fileStream.Read(salt, 0, SaltSize);

        // initialize algorithm with salt
        var keyGenerator = new Rfc2898DeriveBytes(password, SaltSize);
        var rijndael = Rijndael.Create();
        cryptic.IV = keyGenerator.GetBytes(rijndael.BlockSize / 16);
        cryptic.Key = keyGenerator.GetBytes(rijndael.KeySize / 32);

        // decrypt
        CryptoStream crStream = new CryptoStream(stream, cryptic.CreateDecryptor(), CryptoStreamMode.Read);
        StreamReader reader = new StreamReader(crStream);

        string data = reader.ReadToEnd();

        reader.Close();
        stream.Close();
        return data;
    }

}

Encryption is going good and is being written in file. But, while decrypting the file It gives the error "Bad Data". I tried searching for it on SO but it didnt help much.

What Am i doing wrong? Please Help!

I see you reading the salt out of the file, but where are you writing it? — Jonathon Reinhart, May 06 '13 at 12:53
But where are those bytes being written to the output file? You should step through the code to see what they are, and them verify with a hex editor that they are indeed in the output file. — Jonathon Reinhart, May 06 '13 at 12:58
Exactly. Standard approach: look for asymmetry. And you have a `salt` on one side and only a `saltSize` on the other. — H H, May 06 '13 at 13:00
Okay, Edited by code. I am using only "saltSize" now..Still not working — writeToBhuwan, May 06 '13 at 13:23

score 2 · Accepted Answer · edited May 23 '17 at 10:25

2

So, what are you doing wrong.

1st DES has been brute force crackable since the 90's.

2nd you have a different random salt for Encryption and Decryption so you'll never be able to decrypt.

3rd there are a just a lot of mistakes to be made with crypto, it's deceptively easy, either start with a better example or use a highlevel library.

edited May 23 '17 at 10:25

Community

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answered May 06 '13 at 13:30

jbtule

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Bad Data: Cryptography C#

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