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Last Modified: 2013-01-01

Encrypt/decrypt string data stored within sql server 2008

Hi All,

I am pretty new to encryption, as to date I have only had to hash password data without the threat of it being decrypted.

I have done some top level research and understand that there are different algorithms available including both symmetric and asymmetric, and that the .net framework provide excellent security classes.

Within my current solution I have been asked to encrypt only certain table columns within sql server so that the data can only be decrypted by the end user when requesting the data from the asp.net web forms interface.

Can anyone share with me examples or helper class that will provide a sound encryption method that will stop even the nosey web developer from decrypting an end users data?

Should I be encrypting/decrypting using sql server or is it better to using C#?

Thanks in advance for you help and happy new year to you all!

Rit

rito1

Asked: 2012-12-29

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3 Solutions

LVL 16

Imran Javed ZiaConsultant Software Engineer - .NET ArchitectCommented: 2012-12-29

Hi,
you can use both ways: dot net encription/decryption or database column level. Practically i have not used sql server encription, but it is said that sql server encription should be prefered ove dot net encription but you may find following articals helpful:
http://blog.sqlauthority.com/2009/04/28/sql-server-introduction-to-sql-server-encryption-and-symmetric-key-encryption-tutorial-with-script/
http://www.databasejournal.com/features/mssql/article.php/3922881/Column-Level-Encryption-in-SQL-Server.htm
http://stackoverflow.com/questions/5247797/sql-server-vs-net-encryption
Thanks

LVL 1

rito1Author Commented: 2012-12-29

Thanks IJZ for a quick response. It's much appreciated.

The issue I see with your examples is that the developer would be able to use the keys to decrypt the data as the developer would have created them. In my solution it is vital that the developer would be able to decrypt the data. The data should only be decrypted by the end user it belongs to.

Thanks,

Rit

LVL 16

Imran Javed ZiaConsultant Software Engineer - .NET ArchitectCommented: 2012-12-29

then you may need encription and decription on application level rather than database level.

LVL 1

rito1Author Commented: 2012-12-29

Thanks IJZ, do you or anyone have examples of encrypting/decrypting using C# with user defined keys that will fulfil my requirements of the developer not setting or knowing the key?

Thanks,

Rit

LVL 75

Anthony PerkinsCommented: 2012-12-29

The question you need to ask yourself is as follows:
Are the columns that require encryption indexed for searching (used in JOIN and/or WHERE clause). If the answer is yes, then SQL Server's column encryption is not a good fit.

Also, keep in mind that if you have to encrypt the data stored, then you will have to re-design your database in order to use wider varbinary columns instead of for example varchar columns.

LVL 1

rito1Author Commented: 2012-12-30

Thanks acperkins, I have considered this to a certain degree in my design. The columns are not used within joins or indexes.

What I am struggling to find is a sound solution that would stop anyone including myself from decrypting the users data. It's really important that only the end user can encrypt/decrypt their own data.

Can you share with my any examples of this type of solution?

Thank you

Rit

LVL 1

rito1Author Commented: 2012-12-30

... Would it be unusual for the end user to supply a user defined key to encrypt with as part of the save process?... They would then need to supply the same key when retrieving the data too.

LVL 75

Anthony PerkinsCommented: 2012-12-30

I suspect that would be the way to go about it, however I have no experience there, so I am going to leave this to smarter members to help you out.

LVL 35

Robert SchuttSoftware EngineerCommented: 2012-12-31

Sounds to me like you could use AES. I haven't tried to implement it but there is a (rather old but) quite elaborate explanation with C# source code available here: http://msdn.microsoft.com/en-us/magazine/cc164055.aspx

It may be a bit overwhelming (as the author of the article also states) but skimming the article it seems to me you can just add the Aes class file to your project and then use:

Aes a = new Aes(the key size, the seed key);
a.Cipher(plainText, cipherText);

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which would be the content to be encrypted and the user supplied password. The arguments for the constructor are explained in the article but I haven't gone that deep yet...

LVL 35

Robert SchuttSoftware EngineerCommented: 2012-12-31

Ah, looking at the source I found a glitch in my story; the cipherText is the output which leaves me wondering how to set a password or if that's even possible the way I thought it would be...

LVL 35

Robert SchuttSoftware EngineerCommented: 2012-12-31

I made a number of adjustments to the project I found on the page I posted earlier. Not sure if this is the way you want to go, but I made it now so I better post it ;-)

The picture shows a 4th textBox I added for the password as the original code used an all-zeroes password. I also borrowed the idea from a question I worked on earlier to convert the encrypted string to Base64 to make sure it shows without problem in a textBox/web page. That may be overkill when you just want to store the value in a database field. The new code:

private void button1_Click(object sender, System.EventArgs e) {
    byte[] cipherText = Encoding.Unicode.GetBytes(textBox1.Text.PadRight(textBox1.Text.Length + 7 - ((textBox1.Text.Length + 7) % 8), ' '));
    byte[] cipherTextOut = new byte[cipherText.Length];
    byte[] cipherText16 = new byte[16];
    byte[] cipherTextOut16 = new byte[16];
    byte[] passwordBytes = Encoding.Unicode.GetBytes(textBox4.Text.PadRight(8, ' '));
    AesLib.Aes a = new Aes(radioButton1.Checked ? Aes.KeySize.Bits128 : radioButton2.Checked ? Aes.KeySize.Bits192 : Aes.KeySize.Bits256, passwordBytes);
    for (int i = 0; i < cipherText.Length; i += 16) {
        System.Buffer.BlockCopy(cipherText, i, cipherText16, 0, 16);
        a.Cipher(cipherText16, cipherTextOut16);
        System.Buffer.BlockCopy(cipherTextOut16, 0, cipherTextOut, i, 16);
    }
    textBox2.Text = Convert.ToBase64String(cipherTextOut);
}

private void button2_Click(object sender, System.EventArgs e) {
    byte[] cipherText = Convert.FromBase64String(textBox2.Text);
    byte[] decipheredText = new byte[cipherText.Length]; // should always be a multiple of 16
    System.Diagnostics.Debug.Print(cipherText.Length.ToString());
    byte[] cipherText16 = new byte[16];
    byte[] decipheredText16 = new byte[16];
    byte[] passwordBytes = Encoding.Unicode.GetBytes(textBox4.Text.PadRight(8, ' '));
    AesLib.Aes a = new Aes(radioButton1.Checked ? Aes.KeySize.Bits128 : radioButton2.Checked ? Aes.KeySize.Bits192 : Aes.KeySize.Bits256, passwordBytes);
    for (int i = 0; i < cipherText.Length; i += 16) {
        System.Buffer.BlockCopy(cipherText, i, cipherText16, 0, 16);
        a.InvCipher(cipherText16, decipheredText16);
        System.Buffer.BlockCopy(decipheredText16, 0, decipheredText, i, 16);
    }
    textBox3.Text = Encoding.Unicode.GetString(decipheredText).TrimEnd();
}

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LVL 1

rito1Author Commented: 2013-01-01

Thanks Robert, I am checking out that article now.

Yours and everyone's help is much appreciate

Rit

LVL 1

rito1Author Commented: 2013-01-01

Thanks Robert, this is great. I will implement AES and ask the end user for the password to use.

LVL 35

Robert SchuttSoftware EngineerCommented: 2013-01-01

Ok, great, be aware that as far as I can tell what I did with the text, process per 16 byte block, doesn't work for the password, so that's always going to be max 8 (unicode) characters.

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