Develop Reference

Service account cannot load the X509Certificate from windows certificate store

All, I run into an issue where the service account my ASP.NET web forms application (.Net Framework 4.6.1) runs under cannot load the X509Certificate(.pfx) from the personal store on the windows 2012 R2 server .Here is how I imported the certificate to the certificate store
I Logged into the server using the service account(domain\username) ,used mmc snap in to import the certificate to Current User Personal Certificate Store (please see screenshot at the end)
This is the code I am using to load the certificate in C#.But the certificate
is null
public X509Certificate2 Load()
{
X509Certificate2 x509Certificate = null;
var store = new X509Store(StoreName.My,StoreLocation.CurrentUser);
string thumbPrint = StripTheSpacesAndMakeItUpper(ConfigurationManager.AppSettings["pfxthumbPrint"]);
store.Open(OpenFlags.ReadOnly);
var certCollection = store.Certificates;
foreach (var x509 in certCollection)
{
if (x509.Thumbprint.Equals(thumbPrint))
{
x509Certificate = x509;
break;
}
}
store.Close();
return x509Certificate;
}
private string StripTheSpacesAndMakeItUpper(string thumbPrint)
{
if(!string.IsNullOrWhiteSpace(thumbPrint))
{
return Regex.Replace(thumbPrint, #"\s|\W", "").ToUpper();
}
return thumbPrint;
}
Any suggestions on why the method Load returns null ?
]3

I don't know how you set the value of ConfigurationManager.AppSettings["pfxthumbPrint"]. I guess you double clicked the certificate in your CurrentUser store and copied the thumbprint from the Details tab, right? If that is the case, you copied also one invisible character from the beginning of the thumbprint.
The saddest thing is that this character (I don't know what it is) is not visible in your app.config/web.config. The only way to get rid of if is to delete the first quote character with the first character of the thumbprint and type them in again manually. Or delete entire thumbprint and the quotes and type them again if you wish.

Instead of
if (x509.Thumbprint.Equals(x509CertificateFriendlyName))
Shouldn't it be
if (x509.Thumbprint.Equals(thumbPrint))
...?
Also, you appear to have x509Certificate declared as a local variable and then you discard it. Did you intend to assign the value to an instance variable perhaps? I don't even see a return statement.
Also, you're not disposing your store, although that probably isn't the cause of your issue.
Here's a different version that addresses these issues, and will also eliminate any invisible characters in the configuration entry (see pepo's answer for why).
public X509Certificate2 Load()
{
var thumbPrintFromConfig = ConfigurationManager.AppSettings["pfxthumbPrint"]
var thumbPrint = Regex.Replace(thumbPrintFromConfig.ToUpper(),"[^A-F0-9]",""); //Keep only hex digits
return Load(thumbPrint);
}
private X509Certificate2 Load(string thumbPrint)
{
using (var store = new X509Store(StoreName.My,StoreLocation.CurrentUser))
{
store.Open(OpenFlags.ReadOnly);
var cert = store
.Certificates
.OfType<X509Certificate2>()
.Where(x => x.Thumbprint == thumbPrint)
.Single();
store.Close();
return cert;
}
}

CMS signing in .NET with certificate chain not in local trusted certificate store

I have X509 certificates that are stored on the network. I can read the chain from remote windows certificate store. I need to sign some data and include chain to the signature to make it possible to validate it later.
The problem is that I can't find a way to put certificate chain to the CsmSigner. I have read that it takes certificate from constructor parameter and tries to build a chain with X509Chain.Build. It ignores Certificates list values and fails (obviously) because no certificate can be found in the local Windows cert store.
Please find below my test code (that works only if certificates were saved locally to the windows cert store)
protected byte[] SignWithSystem(byte[] data, X509Certificate2 cert, X509Certificate[] chain)
{
ContentInfo contentInfo = new ContentInfo(data);
SignedCms signedCms = new SignedCms(contentInfo, true);
CmsSigner cmsSigner = new CmsSigner(cert);
cmsSigner.DigestAlgorithm = new Oid("2.16.840.1.101.3.4.2.1"); //sha256
cmsSigner.IncludeOption = X509IncludeOption.WholeChain;
if (chain != null)
{
//adding cert chain to signer
cmsSigner.Certificates.AddRange(chain);
signedCms.Certificates.AddRange(chain);
}
signedCms.ComputeSignature(cmsSigner); //fails here with System.Security.Cryptography.CryptographicException : A certificate chain could not be built to a trusted root authority.
byte[] signedPkcs = signedCms.Encode();
return signedPkcs;
}
Is there any way to make it work without uploading certificates to the local store? Should I use any alternative signer?
I can try to upload certificates to the store but the problems are that
I have to add and remove certificates (permissions have to be granted)
There are several processes that applies signature so cross-process synchronization have to be added.
This is not that I'd like to do.

Example CMS Signing with BouncyCastle for .NET
You could use the BouncyCastle crypto library for .NET, which contains its own X509 certificate and CMS signing machinery. A lot of the examples and documentation on the web are for Java, as BouncyCastle was a Java library first. I've used the answer to this Stackoverflow question as a starting point for the certificate and key loading, and added the CMS signing. You may have to tweak parameters to produce the results you want for your use case.
I've made the signing function look approximately like yours, but note the private key is a separate parameter now.
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using Org.BouncyCastle.Cms;
using Org.BouncyCastle.Pkcs;
using Org.BouncyCastle.X509;
using Org.BouncyCastle.Crypto;
using Org.BouncyCastle.X509.Store;
class Program
{
protected static byte[] SignWithSystem(byte[] data, AsymmetricKeyParameter key, X509Certificate cert, X509Certificate[] chain)
{
var generator = new CmsSignedDataGenerator();
// Add signing key
generator.AddSigner(
key,
cert,
"2.16.840.1.101.3.4.2.1"); // SHA256 digest ID
var storeCerts = new List<X509Certificate>();
storeCerts.Add(cert); // NOTE: Adding end certificate too
storeCerts.AddRange(chain); // I'm assuming the chain collection doesn't contain the end certificate already
// Construct a store from the collection of certificates and add to generator
var storeParams = new X509CollectionStoreParameters(storeCerts);
var certStore = X509StoreFactory.Create("CERTIFICATE/COLLECTION", storeParams);
generator.AddCertificates(certStore);
// Generate the signature
var signedData = generator.Generate(
new CmsProcessableByteArray(data),
false); // encapsulate = false for detached signature
return signedData.GetEncoded();
}
static void Main(string[] args)
{
try
{
// Load end certificate and signing key
AsymmetricKeyParameter key;
var signerCert = ReadCertFromFile(#"C:\Temp\David.p12", "pin", out key);
// Read CA cert
var caCert = ReadCertFromFile(#"C:\Temp\CA.cer");
var certChain = new X509Certificate[] { caCert };
var result = SignWithSystem(
Guid.NewGuid().ToByteArray(), // Any old data for sake of example
key,
signerCert,
certChain);
File.WriteAllBytes(#"C:\Temp\Signature.data", result);
}
catch (Exception ex)
{
Console.WriteLine("Failed : " + ex.ToString());
Console.ReadKey();
}
}
public static X509Certificate ReadCertFromFile(string strCertificatePath)
{
// Create file stream object to read certificate
using (var keyStream = new FileStream(strCertificatePath, FileMode.Open, FileAccess.Read))
{
var parser = new X509CertificateParser();
return parser.ReadCertificate(keyStream);
}
}
// This reads a certificate from a file.
// Thanks to: http://blog.softwarecodehelp.com/2009/06/23/CodeForRetrievePublicKeyFromCertificateAndEncryptUsingCertificatePublicKeyForBothJavaC.aspx
public static X509Certificate ReadCertFromFile(string strCertificatePath, string strCertificatePassword, out AsymmetricKeyParameter key)
{
key = null;
// Create file stream object to read certificate
using (var keyStream = new FileStream(strCertificatePath, FileMode.Open, FileAccess.Read))
{
// Read certificate using BouncyCastle component
var inputKeyStore = new Pkcs12Store();
inputKeyStore.Load(keyStream, strCertificatePassword.ToCharArray());
var keyAlias = inputKeyStore.Aliases.Cast<string>().FirstOrDefault(n => inputKeyStore.IsKeyEntry(n));
// Read Key from Aliases
if (keyAlias == null)
throw new NotImplementedException("Alias");
key = inputKeyStore.GetKey(keyAlias).Key;
//Read certificate into 509 format
return (X509Certificate)inputKeyStore.GetCertificate(keyAlias).Certificate;
}
}
}
.NET CMS (Quick-fix with rest of chain omitted from signature)
I can reproduce your problem with a certificate whose root is not in the trusted certificate store, and confirm that adding the certificate chain to the cmsSigner/signedCms Certificates collection does not avoid the A certificate chain could not be built to a trusted root authority error.
You can sign successfully by setting cmsSigner.IncludeOption = X509IncludeOption.EndCertOnly;
However, if you do this, you will not get the rest of the chain in the signature. This probably isn't what you want.
As an aside, in your example you are using X509Certificate for the array of certificates in the chain, but passing them to an X509Certificate2Collection (note the "2" in there). X509Certificate2 derives from X509Certificate, but if its not actually an X509Certificate2 that you put in one of those collections, you'll get a cast error if something iterates over the collection (you don't get an error when adding a certificate of the wrong type unfortunately, because X509Certificate2Collection also derives from X509CertificateCollection and inherits its add methods).

Adding sample code that creates detached PKCS7 signature using BouncyCastle (thanks to softwariness) without Certificate store.
It uses .net X509Certificate2 instances as input parameter. First certificate in collection have to be linked with private key to sign data.
Also I'd like to note that it is not possible to read private key associated with certificate from remote Windows cert store using .net X509Certificate2.PrivateKey property. By default private key is not loaded with certificate using X509Store(#"\\remotemachine\MY", StoreLocation.LocalMachine) and when X509Certificate2.PrivateKey property is accessed on local machine it fails with error "Keyset does not exist".
public void SignWithBouncyCastle(Collection<X509Certificate2> netCertificates)
{
// first cert have to be linked with private key
var signCert = netCertificates[0];
var Cert = Org.BouncyCastle.Security.DotNetUtilities.FromX509Certificate(signCert);
var data = Encoding.ASCII.GetBytes(Cert.SubjectDN.ToString());
var bcCertificates = netCertificates.Select(_ => Org.BouncyCastle.Security.DotNetUtilities.FromX509Certificate(_)).ToList();
var x509Certs = X509StoreFactory.Create("Certificate/Collection", new X509CollectionStoreParameters(bcCertificates));
var msg = new CmsProcessableByteArray(data);
var gen = new CmsSignedDataGenerator();
var privateKey = Org.BouncyCastle.Security.DotNetUtilities.GetKeyPair(signCert.PrivateKey).Private;
gen.AddSigner(privateKey, Cert, CmsSignedDataGenerator.DigestSha256);
gen.AddCertificates(x509Certs);
var signature = gen.Generate(msg, false).GetEncoded();
Trace.TraceInformation("signed");
CheckSignature(data, signature);
Trace.TraceInformation("checked");
try
{
CheckSignature(new byte[100], signature);
}
catch (CryptographicException cex)
{
Trace.TraceInformation("signature was checked for modified data '{0}'", cex.Message);
}
}
void CheckSignature(byte[] data, byte[] signature)
{
var ci = new ContentInfo(data);
SignedCms signedCms = new SignedCms(ci, true);
signedCms.Decode(signature);
foreach (X509Certificate cert in signedCms.Certificates)
Trace.TraceInformation("certificate found {0}", cert.Subject);
signedCms.CheckSignature(true);
}

To be clear, I am no security or cryptography expert.. but per my knowledge, for receiver to be able to validate the signature, the root certificate in the certificate chain you used for signing, must already be a trusted root for the receiver.
If the receiver does not have the root certificate already in their store, and marked as a trusted root... then doesn't matter how you sign the data.. it will fail validation on receiver end. And this is by design.
See more at Chain of trust
Hence the only real solution to your problem I see is to ensure that the root certificate is provisioned as trusted root on both ends... Typically done by a Certificate Authority.
Enterprise application scenario - Typically in an enterprise some group in IT department (who have access to all machines in the domain - like domain admins) would enable this scenario by ensuring that every computer in the domain has root certificate owned by this group, present on every machine as trusted root, and an application developer in the enterprise typically requests a new certificate for use with their application, which has the chain of trust going back to the root certificate already distributed to all machines in the domain.
Found out contact person for this group in your company, and have them issue a certificate you can use for signature.
Internet application scenario - There are established Certificate Authorities, who own their root certificates, and work with OS vendors to ensure that their root certificates are in trusted store, as the OS vendor ships the OS to it's customers. (One reason why using pirated OS can be harmful. It's not just about viruses / malware..). And that is why when you use a certificate issued by VeriSign to sign the data, the signature can be validated by most other machines in the world.

Automated downloading of X509 certificate chain from remote host

I am building some .net code that will run unattended on a scheduled basis on one of our servers. Part of its execution requires that it execute a Java executable which talks to some web resources and services over SSL.
Java will absolutely throw a fit if it's doing something over SSL and it doesn't have every single certificate in the remote certificate's chain. So in .NET I need to be able to specify an https:// resource and need it to download the entire remote chain locally.
Why do I want to do this automatically? Because I want to make deployment simple and to not have to do this 4 times, and then again every time one of Oracle's certificates expires.
I am doing this:
X509Certificate2 lowestCert = SecurityHelper.DownloadSslCertificate(keyDownloadLocation);
X509Chain chain = new X509Chain();
chain.Build(lowestCert);
int counter = 0;
foreach (X509ChainElement el in chain.ChainElements) {
//Extract certificate
X509Certificate2 chainCert = el.Certificate;
//Come up with an alias and save location
string alias = certBaseName + counter;
string localLocation = Path.GetDirectoryName(
System.Reflection.Assembly.GetEntryAssembly().Location
) + #"\" +alias + ".cer";
//Save it locally
SecurityHelper.SaveCertificateToFile(chainCert, localLocation);
//Remove (if possible) and add to java's keystore
deleteKeyFromKeystore(
javaFolder,
alias,
certKeyStore,
SecurityHelper.GetEncryptedAppSetting("JavaKeystorePassword")
);
addKeytoKeyStore(
localLocation,
javaFolder,
alias,
certKeyStore,
SecurityHelper.GetEncryptedAppSetting("JavaKeystorePassword")
);
//Then delete
if (File.Exists(localLocation)) File.Delete(localLocation);
counter++;
}
SecurityHelper.DownloadSslCertificate is a custom method that creates an X509Certificate2 from a a website url.
cert is the lowest-level certificate and I can get that back, but what I can't do is get everything in the chain. chain.ChainElements is still only 1 level deep if the rest of the chain isn't already installed on the machine. My problem is that this is a brand new URL with totally unknown (to the machine) certificates, and I want to go up the stack and recursively download every one.
Is there a way to hit a URL unknown to the machine and programmatically downloading every certificate in the chain?
Edit: here is how I'm downloading the SSL Certificate:
public static X509Certificate2 DownloadSslCertificate(string strDNSEntry)
{
X509Certificate2 cert = null;
using (TcpClient client = new TcpClient())
{
client.Connect(strDNSEntry, 443);
SslStream ssl = new SslStream(client.GetStream(), false,
new RemoteCertificateValidationCallback(
(sender, certificate, chain, sslPolicyErrors) => {
return true;
}
), null);
try
{
ssl.AuthenticateAsClient(strDNSEntry);
}
catch (AuthenticationException e)
{
ssl.Close();
client.Close();
return cert;
}
catch (Exception e)
{
ssl.Close();
client.Close();
return cert;
}
cert = new X509Certificate2(ssl.RemoteCertificate);
ssl.Close();
client.Close();
return cert;
}
}
Edit #2 The solution to obtain remote SSL certificates that worked for me was to capture the chain in the validation callback that occurs during an SslStream.AuthenticateAsClient(url);
private static X509ChainElementCollection callbackChainElements = null;
private static bool CertificateValidationCallback(
Object sender,
X509Certificate certificate,
X509Chain chain,
SslPolicyErrors sslPolicyErrors)
{
callbackChainElements = chain.ChainElements;
return true;
}
And then to kickoff the validation with this callback, I had something like:
public static X509Certificate2 DownloadSslCertificate(string url)
{
X509Certificate2 cert = null;
using (TcpClient client = new TcpClient())
{
client.Connect(url, 443);
SslStream ssl = new SslStream(client.GetStream(), false, CertificateValidationCallback, null);
try
{
ssl.AuthenticateAsClient(url); //will call CertificateValidationCallback
}
... etc
Then by the time AuthenticateAsClient has finished, the local callbackChainElements variable is set to a collection of X509ChainElement.

Actually I did something very similar to this using Powershell.
One piece is changing ServicePointManager to ignore SSL validation (since you may not have the root certs locally, it sounds). It's ServerCertificateValidationCallback that you want to set to true, which tells it you're using a custom validation (or in your case, perhaps no validation).
From there, you're most of the way there with your chainelements. You can use the Export method to export the cert into a byte array:
foreach (X509ChainElement el in chain.ChainElements) {
var certToCreate = el.Certificate.Export(X509ContentType.Cert);
...
}
From there it's just a matter of doing what you want with the byte array. You can pass it to a constructor for another certificate object, which you can then import into the Java keystore.
Hope that helps, please let me know if you have further questions.
EDIT: Actually, I just noticed this post on tips working with X.509 certificates in .NET . The author recommends against writing directly from a byte array because it writes the temp file to a directory that doesn't get cleaned up. So his suggestion is to write the byte array to disk, and then manually clean it up when you're done.

Use a particular CA for a SSL connection

I'm reading through Support Certificates In Your Applications With The .NET Framework 2.0 trying to determine how to set a CA for a SSL connection.
Around half-way down the article under Validating Certificates, MSDN presents some code:
static void ValidateCert(X509Certificate2 cert)
{
X509Chain chain = new X509Chain();
// check entire chain for revocation
chain.ChainPolicy.RevocationFlag = X509RevocationFlag.EntireChain;
// check online and offline revocation lists
chain.ChainPolicy.RevocationMode = X509RevocationMode.Online |
X509RevocationMode.Offline;
// timeout for online revocation list
chain.ChainPolicy.UrlRetrievalTimeout = new TimeSpan(0, 0, 30);
// no exceptions, check all properties
chain.ChainPolicy.VerificationFlags = X509VerificationFlags.NoFlag;
// modify time of verification
chain.ChainPolicy.VerificationTime = new DateTime(1999, 1, 1);
chain.Build(cert);
if (chain.ChainStatus.Length != 0)
Console.WriteLine(chain.ChainStatus[0].Status);
}
Then later:
// override default certificate policy
ServicePointManager.ServerCertificateValidationCallback =
new RemoteCertificateValidationCallback(VerifyServerCertificate);
I feel like I'm missing something really obvious. For example, I don't want a callback - I just want to say, "establish a SSL connection, and here's the one CA to trust". But I don't see that in the code above.
X509Chain does not appear to have an add method to add a CA or root of trust. Shouldn't the CA be set before the callback? But I don't see that in the code above.
In Java, it would be done with a TrustManager (or TrustManagerFactory) after loading the particular CA you want to use (for an example, see Use PEM Encoded CA Cert on filesystem directly for HTTPS request?).
Question: How does one set a CA to use for an SSL connection in .Net or C#?

The following code will avoid the Windows certificate stores and validate the chain with a CA on the filesystem.
The name of the function does not matter. Below, VerifyServerCertificate is the same callback as RemoteCertificateValidationCallback in SslStream class. It can also be used for the ServerCertificateValidationCallback in ServicePointManager.
static bool VerifyServerCertificate(object sender, X509Certificate certificate,
X509Chain chain, SslPolicyErrors sslPolicyErrors)
{
try
{
String CA_FILE = "ca-cert.der";
X509Certificate2 ca = new X509Certificate2(CA_FILE);
X509Chain chain2 = new X509Chain();
chain2.ChainPolicy.ExtraStore.Add(ca);
// Check all properties
chain2.ChainPolicy.VerificationFlags = X509VerificationFlags.NoFlag;
// This setup does not have revocation information
chain2.ChainPolicy.RevocationMode = X509RevocationMode.NoCheck;
// Build the chain
chain2.Build(new X509Certificate2(certificate));
// Are there any failures from building the chain?
if (chain2.ChainStatus.Length == 0)
return false;
// If there is a status, verify the status is NoError
bool result = chain2.ChainStatus[0].Status == X509ChainStatusFlags.NoError;
Debug.Assert(result == true);
return result;
}
catch (Exception ex)
{
Console.WriteLine(ex);
}
return false;
}
I have not figured out how to use this chain (chain2 below) by default such that there's no need for the callback. That is, install it on the ssl socket and the connection will "just work". And I have not figured out how install it such that its passed into the callback. That is, I have to build the chain for each invocation of the callback. I think these are architectural defects in .Net, but I might be missing something obvious.

CertificateStore's Certificates.Find() doesn't actually find the certificate

Here's my simple method:
private static X509Certificate2 GetCertificateFromStore(StoreLocation storeLocation, string certName) {
var store = new X509Store(StoreLocation.LocalMachine);
try {
store.Open(OpenFlags.ReadOnly);
var certs = store.Certificates.Find(X509FindType.FindBySubjectName, certName, true);
return certs.Count == 0 ? null : certs[0];
}
finally {
store.Close();
}
}
Debug locals show that store.Certificates has been loaded and contains two certificates — the default "localhost" one and one I've imported, so the correct store has been successfully opened.
However, the Find() method always returns an empty result, regardless of which certificate I search for and whether I use FindBySubjectName or FindByThumbprint.
Any ideas what could be wrong? It is a simple console app created for the sole purpose of learning & testing certificate loading, i.e., virtually nothing in project configuration or anywhere else is other than default.

Try false as your third parameter to the store.Certificates.Find() method - its possible your your certificates are not valid and are being excluded.