DNX Core: Encrypt/Decrypt? - encryption

Question

I'm porting a website to dnx core/aspnet5/mvc6. I need to store passwords to 3rd party sites in the database (it's essentially an aggregator).
In earlier versions of mvc, I did this using classes like RijndaelManaged. But those don't appear to exist in dnx core. In fact, I haven't been able to find much documentation on any general purpose encryption/decryption stuff in dnx core.
What's the recommended approach for encrypting/decrypting single field values in an mvc6 site? I don't want to encrypt the entire sql server database.
Or should I be looking at a different approach for storing the credentials necessary to access a password-protected 3rd party site?

Answer 1

See the DataProtection API documentation
Their guidance on using it for persistent data protection is a little hedgy but they say there is no technical reason you can't do it. Basically to store protected data persistently you need to be willing to allow unprotecting it with expired keys since the keys could expire after you protect it.
To me it seems reasonable to use it and I am using it in my own project.
Since the IPersistedDataProtector only provides methods with byte arrays I made a couple of extension methods to convert the bytes back and forth from string.
public static class DataProtectionExtensions
{
public static string PersistentUnprotect(
this IPersistedDataProtector dp,
string protectedData,
out bool requiresMigration,
out bool wasRevoked)
{
bool ignoreRevocation = true;
byte[] protectedBytes = Convert.FromBase64String(protectedData);
byte[] unprotectedBytes = dp.DangerousUnprotect(protectedBytes, ignoreRevocation, out requiresMigration, out wasRevoked);
return Encoding.UTF8.GetString(unprotectedBytes);
}
public static string PersistentProtect(
this IPersistedDataProtector dp,
string clearText)
{
byte[] clearBytes = Encoding.UTF8.GetBytes(clearText);
byte[] protectedBytes = dp.Protect(clearBytes);
string result = Convert.ToBase64String(protectedBytes);
return result;
}
}
I also created a helper class specifically for protecting certain properties on my SiteSettings object before it gets persisted to the db.
using cloudscribe.Core.Models;
using Microsoft.AspNet.DataProtection;
using Microsoft.Extensions.Logging;
using System;
namespace cloudscribe.Core.Web.Components
{
public class SiteDataProtector
{
public SiteDataProtector(
IDataProtectionProvider dataProtectionProvider,
ILogger<SiteDataProtector> logger)
{
rawProtector = dataProtectionProvider.CreateProtector("cloudscribe.Core.Models.SiteSettings");
log = logger;
}
private ILogger log;
private IDataProtector rawProtector = null;
private IPersistedDataProtector dataProtector
{
get { return rawProtector as IPersistedDataProtector; }
}
public void Protect(ISiteSettings site)
{
if (site == null) { throw new ArgumentNullException("you must pass in an implementation of ISiteSettings"); }
if (site.IsDataProtected) { return; }
if (dataProtector == null) { return; }
if (site.FacebookAppSecret.Length > 0)
{
try
{
site.FacebookAppSecret = dataProtector.PersistentProtect(site.FacebookAppSecret);
}
catch (System.Security.Cryptography.CryptographicException ex)
{
log.LogError("data protection error", ex);
}
}
// ....
site.IsDataProtected = true;
}
public void UnProtect(ISiteSettings site)
{
bool requiresMigration = false;
bool wasRevoked = false;
if (site == null) { throw new ArgumentNullException("you must pass in an implementation of ISiteSettings"); }
if (!site.IsDataProtected) { return; }
if (site.FacebookAppSecret.Length > 0)
{
try
{
site.FacebookAppSecret = dataProtector.PersistentUnprotect(site.FacebookAppSecret, out requiresMigration, out wasRevoked);
}
catch (System.Security.Cryptography.CryptographicException ex)
{
log.LogError("data protection error", ex);
}
catch (FormatException ex)
{
log.LogError("data protection error", ex);
}
}
site.IsDataProtected = false;
if (requiresMigration || wasRevoked)
{
log.LogWarning("DataProtection key wasRevoked or requires migration, save site settings for " + site.SiteName + " to protect with a new key");
}
}
}
}
If the app will need to migrate to other machines after data has been protected then you also want to take control of the key location, the default would put the keys on the OS keyring of the machine as I understand it so a lot like machinekey in the past where you would override it in web.config to be portable.
Of course protecting the keys is on you at this point. I have code like this in the startup of my project
//If you change the key persistence location, the system will no longer automatically encrypt keys
// at rest since it doesn’t know whether DPAPI is an appropriate encryption mechanism.
services.ConfigureDataProtection(configure =>
{
string pathToCryptoKeys = appBasePath + Path.DirectorySeparatorChar
+ "dp_keys" + Path.DirectorySeparatorChar;
// these keys are not encrypted at rest
// since we have specified a non default location
// that also makes the key portable so they will still work if we migrate to
// a new machine (will they work on different OS? I think so)
// this is a similar server migration issue as the old machinekey
// where we specified a machinekey in web.config so it would not change if we
// migrate to a new server
configure.PersistKeysToFileSystem(new DirectoryInfo(pathToCryptoKeys));
});
So my keys are stored in appRoot/dp_keys in this example.

Answer 2

If you want to do things manually;
Add a reference to System.Security.Cryptography.Algorithms
Then you can create instances of each algorithm type via the create method. For example;
var aes = System.Security.Cryptography.Aes.Create();