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How to: Use Data Protection

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Note

This article applies to Windows.

For information about ASP.NET Core, see ASP.NET Core Data Protection.

.NET provides access to the data protection API (DPAPI), which allows you to encrypt data using information from the current user account or computer. When you use the DPAPI, you alleviate the difficult problem of explicitly generating and storing a cryptographic key.

Use the ProtectedData class to encrypt a copy of an array of bytes. You can specify that data encrypted by the current user account can be decrypted only by the same user account, or you can specify that data encrypted by the current user account can be decrypted by any account on the computer. See the DataProtectionScope enumeration for a detailed description of ProtectedData options.

Encrypt data to a file or stream using data protection

  1. Create random entropy.

  2. Call the static Protect method while passing an array of bytes to encrypt, the entropy, and the data protection scope.

  3. Write the encrypted data to a file or stream.

To decrypt data from a file or stream using data protection

  1. Read the encrypted data from a file or stream.

  2. Call the static Unprotect method while passing an array of bytes to decrypt and the data protection scope.

Example

The following code example demonstrates two forms of encryption and decryption. First, the code example encrypts and then decrypts an in-memory array of bytes. Next, the code example encrypts a copy of a byte array, saves it to a file, loads the data back from the file, and then decrypts the data. The example displays the original data, the encrypted data, and the decrypted data.

C# 
using System;
using System.IO;
using System.Text;
using System.Security.Cryptography;

public class MemoryProtectionSample
{
    public static void Main() => Run();

    public static void Run()
    {
        try
        {
            ///////////////////////////////
            //
            // Memory Encryption - ProtectedMemory
            //
            ///////////////////////////////

            // Create the original data to be encrypted (The data length should be a multiple of 16).
            byte[] toEncrypt = UnicodeEncoding.ASCII.GetBytes("ThisIsSomeData16");

            Console.WriteLine($"Original data: {UnicodeEncoding.ASCII.GetString(toEncrypt)}");
            Console.WriteLine("Encrypting...");

            // Encrypt the data in memory.
            EncryptInMemoryData(toEncrypt, MemoryProtectionScope.SameLogon);

            Console.WriteLine($"Encrypted data: {UnicodeEncoding.ASCII.GetString(toEncrypt)}");
            Console.WriteLine("Decrypting...");

            // Decrypt the data in memory.
            DecryptInMemoryData(toEncrypt, MemoryProtectionScope.SameLogon);

            Console.WriteLine($"Decrypted data: {UnicodeEncoding.ASCII.GetString(toEncrypt)}");

            ///////////////////////////////
            //
            // Data Encryption - ProtectedData
            //
            ///////////////////////////////

            // Create the original data to be encrypted
            toEncrypt = UnicodeEncoding.ASCII.GetBytes("This is some data of any length.");

            // Create a file.
            FileStream fStream = new FileStream("Data.dat", FileMode.OpenOrCreate);

            // Create some random entropy.
            byte[] entropy = CreateRandomEntropy();

            Console.WriteLine();
            Console.WriteLine($"Original data: {UnicodeEncoding.ASCII.GetString(toEncrypt)}");
            Console.WriteLine("Encrypting and writing to disk...");

            // Encrypt a copy of the data to the stream.
            int bytesWritten = EncryptDataToStream(toEncrypt, entropy, DataProtectionScope.CurrentUser, fStream);

            fStream.Close();

            Console.WriteLine("Reading data from disk and decrypting...");

            // Open the file.
            fStream = new FileStream("Data.dat", FileMode.Open);

            // Read from the stream and decrypt the data.
            byte[] decryptData = DecryptDataFromStream(entropy, DataProtectionScope.CurrentUser, fStream, bytesWritten);

            fStream.Close();

            Console.WriteLine($"Decrypted data: {UnicodeEncoding.ASCII.GetString(decryptData)}");
        }
        catch (Exception e)
        {
            Console.WriteLine($"ERROR: {e.Message}");
        }
    }

    public static void EncryptInMemoryData(byte[] Buffer, MemoryProtectionScope Scope )
    {
        if (Buffer == null)
            throw new ArgumentNullException(nameof(Buffer));
        if (Buffer.Length <= 0)
            throw new ArgumentException("The buffer length was 0.", nameof(Buffer));

        // Encrypt the data in memory. The result is stored in the same array as the original data.
        ProtectedMemory.Protect(Buffer, Scope);
    }

    public static void DecryptInMemoryData(byte[] Buffer, MemoryProtectionScope Scope)
    {
        if (Buffer == null)
            throw new ArgumentNullException(nameof(Buffer));
        if (Buffer.Length <= 0)
            throw new ArgumentException("The buffer length was 0.", nameof(Buffer));

        // Decrypt the data in memory. The result is stored in the same array as the original data.
        ProtectedMemory.Unprotect(Buffer, Scope);
    }

    public static byte[] CreateRandomEntropy()
    {
        // Create a byte array to hold the random value.
        byte[] entropy = new byte[16];

        // Create a new instance of the RNGCryptoServiceProvider.
        // Fill the array with a random value.
        new RNGCryptoServiceProvider().GetBytes(entropy);

        // Return the array.
        return entropy;
    }

    public static int EncryptDataToStream(byte[] Buffer, byte[] Entropy, DataProtectionScope Scope, Stream S)
    {
        if (Buffer == null)
            throw new ArgumentNullException(nameof(Buffer));
        if (Buffer.Length <= 0)
            throw new ArgumentException("The buffer length was 0.", nameof(Buffer));
        if (Entropy == null)
            throw new ArgumentNullException(nameof(Entropy));
        if (Entropy.Length <= 0)
            throw new ArgumentException("The entropy length was 0.", nameof(Entropy));
        if (S == null)
            throw new ArgumentNullException(nameof(S));

        int length = 0;

        // Encrypt the data and store the result in a new byte array. The original data remains unchanged.
        byte[] encryptedData = ProtectedData.Protect(Buffer, Entropy, Scope);

        // Write the encrypted data to a stream.
        if (S.CanWrite && encryptedData != null)
        {
            S.Write(encryptedData, 0, encryptedData.Length);

            length = encryptedData.Length;
        }

        // Return the length that was written to the stream.
        return length;
    }

    public static byte[] DecryptDataFromStream(byte[] Entropy, DataProtectionScope Scope, Stream S, int Length)
    {
        if (S == null)
            throw new ArgumentNullException(nameof(S));
        if (Length <= 0 )
            throw new ArgumentException("The given length was 0.", nameof(Length));
        if (Entropy == null)
            throw new ArgumentNullException(nameof(Entropy));
        if (Entropy.Length <= 0)
            throw new ArgumentException("The entropy length was 0.", nameof(Entropy));

        byte[] inBuffer = new byte[Length];
        byte[] outBuffer;

        // Read the encrypted data from a stream.
        if (S.CanRead)
        {
            S.Read(inBuffer, 0, Length);

            outBuffer = ProtectedData.Unprotect(inBuffer, Entropy, Scope);
        }
        else
        {
            throw new IOException("Could not read the stream.");
        }

        // Return the decrypted data
        return outBuffer;
    }
}

Compiling the Code

This example compiles and runs only when targeting .NET Framework and running on Windows.

See also