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C# - Looking for Encryption/Decryption Method

I've written a C# piece that encrypts/decrypts a string using RtlEncryptMemory/RtlDecryptMemory. This string is then saved in a config file, it all works well but the problem is that once I logoff/logon, I can no longer decrypt the string. I am using the RTL_ENCRYPT_OPTION_SAME_LOGON option which means the internal mechanism uses something from the Windows session in order to perform the decryption. I am looking for a solution that works in the same manner but is tied to the network user (or token, etc...). Is Windows providing something already?
My goal is to be able to decrypt the string from anywhere as long as the process is running under the same user (network credentials). I also do not want to have the user type in a password or use an internal value as that could be compromised. Ideally it would be just like the RTL functions but provide an RTL_ENCRYPT_OPTION_SAME_USER option.

You want to use the DataProtection API
Here is a simple implementation that adds Encrypt and Decrypt string extensions...
public static class StringExtensions
{
public static string Encrypt(this string s)
{
if (String.IsNullOrEmpty(s))
{
return s;
}
else
{
var encoding = new UTF8Encoding();
byte[] plain = encoding.GetBytes(s);
byte[] secret = ProtectedData.Protect(plain, null, DataProtectionScope.CurrentUser);
return Convert.ToBase64String(secret);
}
}
public static string Decrypt(this string s)
{
if (String.IsNullOrEmpty(s))
{
return s;
}
else
{
byte[] secret = Convert.FromBase64String(s);
byte[] plain = ProtectedData.Unprotect(secret, null, DataProtectionScope.CurrentUser);
var encoding = new UTF8Encoding();
return encoding.GetString(plain);
}
}
}
Here is an example...
class Program
{
static void Main(string[] args)
{
string password = "Monkey123";
string encrypted = password.Encrypt();
Console.WriteLine($"Encrypted password = '{encrypted}'");
string decrypted = encrypted.Decrypt();
Console.WriteLine($"Decrypted password = '{decrypted}'");
}
}
Which produces this output...
Encrypted password = 'AQAAANCMnd8BFdERjHoAwE/Cl+sBAAAA/6wDgM21DkStrNJQ35QDiwAAAAACAAAAAAAQZgAAAAEAACAAAAAPr3/aqafbt/RRoPVe75b+PFBhE6h9MLcQ2Ivsd3adOwAAAAAOgAAAAAIAACAAAABYxqEdzotL+7qXpWnbbpPRkfWZF6oh/meFsXzFtLPnrBAAAAB59VGbboP4Tye1N3dB7E3jQAAAAMQn8cAlnTDe1mwDEJriADizdT2Qr0DtPgpMje+rbjdkVpL+cKiEQs4om4i1hlLPgPn5MG5oVWFFnxU0d4c9TFg='
Decrypted password = 'Monkey123'
Notes:
Only the currently logged in user can decrypt the data encrypted with this code. This works across the network as long as the current user has a roaming profile.
Alternatively the scope can be local machine in which case only users logged in to the same machine can decrypt the data.
This is .NET Core 3.1 code and works only on Windows machines
Using statements...
using System;
using System.Security.Cryptography;
using System.Text;

You should not be using RtlEncryptMemory if you want to store the string, it is meant to only keep strings secure inside the running applications memory, it therefore can be stored/serialized and decrypted.
Have a look at DPAPI password encryption I think it should meet your needs.

I have a Nuget package you might like:
DataJuggler.Net.Cryptography .Net Framework
DataJuggler.Core.Cryptography Dot Net Core
Pretty simple to work with, here is a live demo:
https://blazorcrypto.datajuggler.com/
Source code and video link is available above also.
Usage:
Encryption:
// get the encryptedText
encryptedResult = CryptographyHelper.EncryptString(textToEncrypt, keyCode);
Decryption:
// get thedecryptedText
decryptedResult = CryptographyHelper.DecryptString(textToDecrypt, keyCode);
It also includes password hashing.
Let me know if you think it is worth the price of free.

DPAPI fails with CryptographicException when trying to decrypt Chrome cookies

i am trying to get session from my Chrome browser. i can see 2 cookie files in Developer Tools. but this is inconvenient for the user to get cookie values from browser, i would like to do it in code. so i use this code to get Chrome default profile cookie sqlite DB:
string local = Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData);
string path = #"Google\Chrome\User Data\Default\Cookies";
path = Path.Combine(local, path);
next i create SQLite connection and request
var cmd = new SQLiteCommand("SELECT encrypted_value, name FROM cookies WHERE host_key = 'my_host_ip'", con);
then i read the results
byte[] encryptedCookie = (byte[])r.GetValue(r.GetOrdinal("encrypted_value"));
and try to decrypt it:
var decodedData = ProtectedData.Unprotect(encryptedCookie, null, DataProtectionScope.CurrentUser);
var plainText = Encoding.ASCII.GetString(decodedData);
and here i got exception
System.Security.Cryptography.CryptographicException
i know that i MUST decrypt cookie contents under the same user account under which the browser was launched (on the same machine), and parameter DataProtectionScope.CurrentUser is used for that
i see 63 bytes in debugger (in encryptedCookie array), i also see this bytes in SQLite DB BLOB field.
but Unprotect method throws System.Security.Cryptography.CryptographicException: Invalid data error.
my code works fine at 5 different PC's in my office (win10, win7), but didnt work on my developer PC (win10, vs2019).
i think that the problem is in my Windows Settings or somewhere else, not in my code. so what i am doing wrong?
interesting note - i found PowerShell script that does the same thing (through Add-Type -AssemblyName System.Security) - get cookie and decrypt it. this script also works fine at 5 office PC's, but didnt work at my PC.
my Windows installation is new, i have no AV software. we connected to the same Corporate domain and we have the same security settings.
UPD 1
a little expreriment:
get cookie value from Chrome browser (32 chars, JSESSIONID)
create a simple app that protects this value with CurrentUser protection scope. now i have an array of 178 bytes (result #1)
view Chrome's cookies database with a) https://sqliteonline.com/ and b) DataBase.Net desktop app. this two methods give me the same result: only 63 bytes of encrypted cookie data (result #2). i can also get the same result with my c# application using System.Data.SQLite
so, the results are not equal in length or content
result #1 != result #2
looks like Chrome's cookie value protected by different scope (maybe admin account?), but i see my user account name in Task Manager in Chrome's process
P.S. i use .net 4.7.2
UPD 2
i found this method in Chromium sources
bool OSCrypt::DecryptString(const std::string& ciphertext,
std::string* plaintext) {
if (!base::StartsWith(ciphertext, kEncryptionVersionPrefix,
base::CompareCase::SENSITIVE))
return DecryptStringWithDPAPI(ciphertext, plaintext);
crypto::Aead aead(crypto::Aead::AES_256_GCM);
auto key = GetEncryptionKeyInternal();
aead.Init(&key);
// Obtain the nonce.
std::string nonce =
ciphertext.substr(sizeof(kEncryptionVersionPrefix) - 1, kNonceLength);
// Strip off the versioning prefix before decrypting.
std::string raw_ciphertext =
ciphertext.substr(kNonceLength + (sizeof(kEncryptionVersionPrefix) - 1));
return aead.Open(raw_ciphertext, nonce, std::string(), plaintext);
}
so DPAPI is only used when BLOB NOT starts with v10 chars. but my cookie BLOBs starts with v10 chars, and, according to the code, another crypto-algorithm is used, but i dont understand WHY.

I finally figured it out. according to Chromium sources, two methods are used to decrypt the cookie value.
if the cookie value starts with v10 chars, we use AES_256_GCM
otherwise, DPAPI is used
for the first method we need key and nonce. key is located in Google Chrome files and nonce is located in encrypted cookie value.
it remains unclear for me - what determines which method is used

For people who are looking for the code, I'm expanding on Cerberus answer. Starting Chrome 80 version, cookies are encrypted using the AES256-GCM algorithm, and the AES encryption key is encrypted with the DPAPI encryption system, and the encrypted key is stored inside the ‘Local State’ file.
byte[] encryptedData=<data stored in cookie file>
string encKey = File.ReadAllText(localAppDataPath + #"\Google\Chrome\User Data\Local State");
encKey = JObject.Parse(encKey)["os_crypt"]["encrypted_key"].ToString();
var decodedKey = System.Security.Cryptography.ProtectedData.Unprotect(Convert.FromBase64String(encKey).Skip(5).ToArray(), null, System.Security.Cryptography.DataProtectionScope.LocalMachine);
_cookie = _decryptWithKey(encryptedData, decodedKey, 3);
Key size is 256 bits. Encypted message format is, pay load('v12')+nonce (12 bytes)+cipherText
private string _decryptWithKey(byte[] message, byte[] key, int nonSecretPayloadLength)
{
const int KEY_BIT_SIZE = 256;
const int MAC_BIT_SIZE = 128;
const int NONCE_BIT_SIZE = 96;
if (key == null || key.Length != KEY_BIT_SIZE / 8)
throw new ArgumentException(String.Format("Key needs to be {0} bit!", KEY_BIT_SIZE), "key");
if (message == null || message.Length == 0)
throw new ArgumentException("Message required!", "message");
using (var cipherStream = new MemoryStream(message))
using (var cipherReader = new BinaryReader(cipherStream))
{
var nonSecretPayload = cipherReader.ReadBytes(nonSecretPayloadLength);
var nonce = cipherReader.ReadBytes(NONCE_BIT_SIZE / 8);
var cipher = new GcmBlockCipher(new AesEngine());
var parameters = new AeadParameters(new KeyParameter(key), MAC_BIT_SIZE, nonce);
cipher.Init(false, parameters);
var cipherText = cipherReader.ReadBytes(message.Length);
var plainText = new byte[cipher.GetOutputSize(cipherText.Length)];
try
{
var len = cipher.ProcessBytes(cipherText, 0, cipherText.Length, plainText, 0);
cipher.DoFinal(plainText, len);
}
catch (InvalidCipherTextException)
{
return null;
}
return Encoding.Default.GetString(plainText);
}
}
Needed packages
1) Newtonsoft JSON .net
2) Bouncy Castle Crypto package

How do I use the private key from a PFX certificate stored in Azure Key Vault in .NET Core 2?

I've written an ASP.NET Core 2.0 website in C# and have Facebook authentication enabled, so it requires HTTPS. I'm using the native Kestrel web server to host the site and have a listener set to take the PFX certificate per MS' documentation. I can't seem to find a way for Kestrel to recognize the private key after recall from Key Vault. I know it's present, as I wrote two debug statements that indicate it is, in fact present.
This is the function that I'm using to retrieve the secret, which is working.
public static async Task<X509Certificate2> GetKeyVaultCert()
{
X509Certificate2 pfx;
try
{
var kvClient = new KeyVaultClient(new KeyVaultClient.AuthenticationCallback(GetToken));
var secret = await kvClient
.GetSecretAsync("https://macscampvault.vault.azure.net/secrets/letsencrypt").ConfigureAwait(false);
byte[] bytes;
if(secret.ContentType == "application/x-pkcs12")
bytes = Convert.FromBase64String(secret.Value);
else
{
bytes = new byte[0];
Console.WriteLine("secret is not PFX!!");
throw new ArgumentException("This is not a PFX string!!");
}
var password = new SecureString();
var coll = new X509Certificate2Collection();
coll.Import(bytes, null, X509KeyStorageFlags.Exportable);
pfx = coll[0];
// File output added in case I end up needing to write cert to container
// File.WriteAllBytes(Directory.GetCurrentDirectory().ToString() + "/Macs.pfx", bytes);
Console.WriteLine(pfx.HasPrivateKey);
Console.WriteLine(pfx.GetRSAPrivateKey());
}
catch (Exception ex)
{
Console.WriteLine($"There was a problem during the key vault operation\n{ex.Message}");
throw;
}
return pfx;
}
The debug statements after the assignment call pfx = coll[0]; tell me that this private key exists, but when I try to connect to the website using lynx https://localhost I receive the following exception:
System.NotSupportedException: The server mode SSL must use a certificate with the associated private key.
So, how do I use the private key? Here's a gist to the file in question.
I already was helped by How to serialize and deserialize a PFX certificate in Azure Key Vault? but after following it, I got to this state.

In your gist you have the following code:
var keyVaultCert = GetKeyVaultCert().Result ??
throw new ArgumentNullException("GetKeyVaultCert().Result");
pfx = new X509Certificate2(keyVaultCert.RawData);
The second line there removes the private key, because the RawData property just returns the DER encoded X.509 object.
keyVaultCert is already an X509Certificate2 with a private key, you probably want to just use it.
pfx = GetKeyVaultCert().Result ?? throw etc;

How to ensure X509Certificate2 class does not return duplicate signing certificates?

I have a C# windows form application. The user types in message, subject, to, and selects a signing certificate from a drop down to sign the email as well using X509Certificate2 class.
Here is how the snippet for how the dropdown (ComboBox SigningCertList) is populated:
try
{
X509Certificate2[] certs;
certs = CryptoHelper.GetSigningCertificateList();
SigningCertList.Items.AddRange(certs);
SigningCertList.ValueMember = "SerialNumber";
SigningCertList.DisplayMember = "FriendlyName";
SigningCertList.SelectedIndexChanged += new System.EventHandler(SigningCertList_SelectedIndexChanged);
SigningCertList.SelectedItem = 0;
}
Symptoms are odd. The combobox will show my signing certificate (installed from a p12 file). However, if I load the Windows Certificates MMC snapin, I cannot find it when doing a search. Upon reinstalling the certificate, I see it in the Windows Certificates MMC snapin, and now duplicated in the dropdown. Only the second (or last / recent) signing cert in the list actually signs it.
So how can I ensure X509Certificate2 class does not return duplicate signing certificates?
Here is the GetSigningCertificateList() method below:
`public static X509Certificate2[] GetSigningCertificateList()
{
var list = new List();
int matches = 0;
X509Store localStore = new X509Store(StoreLocation.LocalMachine);
localStore.Open(OpenFlags.ReadOnly | OpenFlags.OpenExistingOnly);
try
{
foreach (X509Certificate2 cert in localStore.Certificates)
{
foreach (X509Extension extension in cert.Extensions)
{
X509KeyUsageExtension usageExtension = extension as X509KeyUsageExtension;
if (usageExtension != null)
{
bool matchesUsageRequirements = ((X509KeyUsageFlags.DigitalSignature & usageExtension.KeyUsages) == X509KeyUsageFlags.DigitalSignature);
if (matchesUsageRequirements)
{
list.Add(cert);
matches += 1;
}
}
}
}
}
finally
{
localStore.Close();
}
X509Store userStore = new X509Store(StoreLocation.CurrentUser);
userStore.Open(OpenFlags.ReadOnly | OpenFlags.OpenExistingOnly);
try
{
foreach (X509Certificate2 cert in userStore.Certificates)
{
foreach (X509Extension extension in cert.Extensions)
{
X509KeyUsageExtension usageExtension = extension as X509KeyUsageExtension;
if (usageExtension != null)
{
bool matchesUsageRequirements = ((X509KeyUsageFlags.DigitalSignature & usageExtension.KeyUsages) == X509KeyUsageFlags.DigitalSignature);
if ((matchesUsageRequirements) && cert.FriendlyName.IndexOf("MYcompanyname.",0) >= 0)
{
list.Add(cert);
matches += 1;
}
}
}
}
}
finally
{
userStore.Close();
}
return list.ToArray();
}
}`

You mention that you don't see a cert in MMC, but do in your app; and that when you install the cert via MMC it shows up twice. This suggests that you're using MMC to view the user My store (or the computer My store) but the certificate in question is normally present in the other location.
Once the certificate has been registered in two different stores (same store name, different location => different store) then Windows no longer considers it to be a duplicate (for one, the two instances can have different private key permissions). So while there's a duplicate to your application, there's not (intrinsically) to Windows or .NET.
You can prevent duplicates by standard dedup tactics, such as using a HashSet<X509Certificate2> instead of a List<X509Certificate2>. The default .Equals check (which is performed by the default comparator) will match if the issuer and serial number are the same. That should be unique as long as your certificates come from a public CA; but private PKI could recycle serial numbers or not guarantee uniqueness. If you're concerned you could use a custom comparator which uses whatever match logic you like.
So the easy dedup is to replace list = new List<X509Certificate2>() with list = new HashSet<X509Certificate2>() (though you should probably change the variable name).
A HashSet keeps only the first of the collisions; so if you want LocalMachine to be preferred you've already achieved that. If CurrentUser should win, you may want to switch your blocks around.
Two other things of note:
If a certificate has no key usage extension at all it's considered valid for all usages. Your code doesn't do that. (If you know that a "correct" cert in your application always will then there's no problem)
X509Store.Certificates returns new objects every call; you could reduce finalizations by calling Dispose on the certificates you don't return (or Reset for .NET 4.5.2 and below).

Using certificate file to connect to webservice over SSL

I am developing windows service in C# which invokes webservice methods. I must use SSL to connect to webservice. I have recieved from publisher p12 file with certificate. The file is password protected. To use Import method to use this certificate. Everything is working fine, but I do not like this method - I have password harcoded in my app. When publisher changes certificate I must rewrite code(changing the password to new one). Is there any way not to harcode password to .p12 file or use other option(.cer file)?

What you could do is something like this:
Install the SSL certificate into your local machine certificate store (using the Microsoft Management Console "MMC")
Extract the certificates thumbprint (e.g. "748681ca3646ccc7c4facb7360a0e3baa0894cb5")
Use a function which fetches you the certificate from the local certificate store for the given thumbprint.
Provide the SSL certificate when calling your web service.
private static X509Certificate2 GetCertificateByThumbprint(string certificateThumbPrint, StoreLocation certificateStoreLocation) {
X509Certificate2 certificate = null;
X509Store certificateStore = new X509Store(certificateStoreLocation);
certificateStore.Open(OpenFlags.ReadOnly);
X509Certificate2Collection certCollection = certificateStore.Certificates;
foreach (X509Certificate2 cert in certCollection)
{
if (cert.Thumbprint != null && cert.Thumbprint.Equals(certificateThumbPrint, StringComparison.OrdinalIgnoreCase))
{
certificate = cert;
break;
}
}
if (certificate == null)
{
Log.ErrorFormat(CultureInfo.InvariantCulture, "Certificate with thumbprint {0} not found", certificateThumbPrint);
}
return certificate;
}
public string GetServiceResponse() {
string WebSvcEndpointConfigurationName = "WebServiceEndpoint";
Uri webSvcEndpointAddress = new Uri("http://www.example.com/YourWebService.svc");
string webSvcCertificateThumbPrint = "748681ca3646ccc7c4facb7360a0e3baa0894cb5";
string webSvcResponse = null;
SomeWebServiceClient webServiceClient = null;
try
{
webServiceClient = new SomeWebServiceClient(WebSvcEndpointConfigurationName, new EndpointAddress(webSvcEndpointAddress));
webServiceClient.ClientCredentials.ClientCertificate.Certificate = GetCertificateByThumbprint(webSvcCertificateThumbPrint, StoreLocation.LocalMachine);
webSvcResponse = webServiceClient.GetServiceResponse();
}
catch (Exception ex)
{
}
finally
{
if (webServiceClient != null)
{
webServiceClient.Close();
}
}
return webSvcResponse;
}

PKCS#12 file is provided to you as it is a natural way to transport certificates together with private keys. You can use one of the following:
convert it to format you like and store the way you like
convert it to passwordless PFX
import it to computer's certificate storage and use it this way
But all those methods (together with keeping a hardcoded password) provide no real protection to the private key and thus are not usable if you distribute the application to outside of your organization.