Develop Reference

C# Add two HTTPS bindings with two different certificate with the ServerManager not working

I am trying to create two different bindings on two different site on IIS with C# from my website.
Those 2 binding needs to be set with a certificate (one specific for each bindings). The problem is, the bindings are correctly created but the two bindings are created with the same certificate.
Here my code :
public async Task AddBindings(string code)
{
await AddBinding("Website1", "website1.com");
await AddBinding("Website2", "website2.com");
}
private async Task AddBinding(string siteName, string urlDomain)
{
using (ServerManager serverMgr = new ServerManager())
{
var site = serverMgr.Sites[siteName];
var certif = GetCertificate("*." + urlDomain);
site.Bindings.Add("*:443:" + urlDomain, certif.GetCertHash(), "My");
serverMgr.CommitChanges();
serverMgr.Dispose();
}
}
private X509Certificate2 GetCertificate(string nameStartWith)
{
var store = new X509Store(StoreName.My, StoreLocation.LocalMachine);
store.Open(OpenFlags.OpenExistingOnly);
X509Certificate2 certif = null;
foreach (var certificate in store.Certificates)
{
var certifDate = DateTime.Parse(certificate.GetEffectiveDateString());
if (certificate.FriendlyName.StartsWith(nameStartWith))
{
certif = certificate;
}
}
store.Close();
return certif;
}
The "funny things" in the function AddBindings, in this order the two bindings are going to be created with the Website2 certificate, and if I change the order of the two rows it's going to use Website1.
Thank you very much for your helps !

Your code definitely leads to that, because nowhere you specify that SNI mappings should be used.
The correct function call you should make is this overloading version,
Add (string bindingInformation, byte[] certificateHash, string certificateStoreName, Microsoft.Web.Administration.SslFlags sslFlags)
You can read more about SNI mappings in Windows HTTP API from here.

Digital signature show wrong sign date

I am learning digital signature and how to sign it in c#.Here is my code:
Signature.cs
public class Signature
{
static readonly string RT_OfficeDocument = "http://schemas.openxmlformats.org/officeDocument/2006/relationships/officeDocument";
static readonly string OfficeObjectID = "idOfficeObject";
static readonly string SignatureID = "idPackageSignature";
static readonly string ManifestHashAlgorithm = "http://www.w3.org/2000/09/xmldsig#sha1";
// Entry Point
public static void DigiSign(string tempfile)
{
// Open the Package
using (Package package = Package.Open(tempfile))
{
// Get the certificate
X509Certificate2 certificate = GetCertificate();
SignAllParts(package, certificate);
}
}
private static void SignAllParts(Package package, X509Certificate certificate)
{
if (package == null) throw new ArgumentNullException("SignAllParts(package)");
List<Uri> PartstobeSigned = new List<Uri>();
List<PackageRelationshipSelector> SignableReleationships = new List<PackageRelationshipSelector>();
foreach (PackageRelationship relationship in package.GetRelationshipsByType(RT_OfficeDocument))
{
// Pass the releationship of the root. This is decided based on the RT_OfficeDocument (http://schemas.openxmlformats.org/officeDocument/2006/relationships/officeDocument)
CreateListOfSignableItems(relationship, PartstobeSigned, SignableReleationships);
}
// Create the DigitalSignature Manager
PackageDigitalSignatureManager dsm = new PackageDigitalSignatureManager(package);
dsm.CertificateOption = CertificateEmbeddingOption.InSignaturePart;
string signatureID = SignatureID;
string manifestHashAlgorithm = ManifestHashAlgorithm;
System.Security.Cryptography.Xml.DataObject officeObject = CreateOfficeObject(signatureID, manifestHashAlgorithm);
Reference officeObjectReference = new Reference("#" + OfficeObjectID);
try
{
dsm.Sign(PartstobeSigned, certificate, SignableReleationships, signatureID, new System.Security.Cryptography.Xml.DataObject[] { officeObject }, new Reference[] { officeObjectReference });
}
catch (CryptographicException ex)
{
Console.WriteLine(ex.InnerException.ToString());
}
}// end:SignAllParts()
/**************************SignDocument******************************/
// This function is a helper function. The main role of this function is to
// create two lists, one with Package Parts that you want to sign, the other
// containing PacakgeRelationshipSelector objects which indicate relationships to sign.
/*******************************************************************/
static void CreateListOfSignableItems(PackageRelationship relationship, List<Uri> PartstobeSigned, List<PackageRelationshipSelector> SignableReleationships)
{
// This function adds the releation to SignableReleationships. And then it gets the part based on the releationship. Parts URI gets added to the PartstobeSigned list.
PackageRelationshipSelector selector = new PackageRelationshipSelector(relationship.SourceUri, PackageRelationshipSelectorType.Id, relationship.Id);
SignableReleationships.Add(selector);
if (relationship.TargetMode == TargetMode.Internal)
{
PackagePart part = relationship.Package.GetPart(PackUriHelper.ResolvePartUri(relationship.SourceUri, relationship.TargetUri));
if (PartstobeSigned.Contains(part.Uri) == false)
{
PartstobeSigned.Add(part.Uri);
// GetRelationships Function: Returns a Collection Of all the releationships that are owned by the part.
foreach (PackageRelationship childRelationship in part.GetRelationships())
{
CreateListOfSignableItems(childRelationship, PartstobeSigned, SignableReleationships);
}
}
}
}
/**************************SignDocument******************************/
// Once you create the list and try to sign it, Office will not validate the Signature.
// To allow Office to validate the signature, it requires a custom object which should be added to the
// signature parts. This function loads the OfficeObject.xml resource.
// Please note that GUID being passed in document.Loadxml.
// Background Information: Once you add a SignatureLine in Word, Word gives a unique GUID to it. Now while loading the
// OfficeObject.xml, we need to make sure that The this GUID should match to the ID of the signature line.
// So if you are generating a SignatureLine programmtically, then mmake sure that you generate the GUID for the
// SignatureLine and for this element.
/*******************************************************************/
static System.Security.Cryptography.Xml.DataObject CreateOfficeObject(
string signatureID, string manifestHashAlgorithm)
{
XmlDocument document = new XmlDocument();
document.LoadXml(String.Format(Properties.Resources.OfficeObject, signatureID, manifestHashAlgorithm, "{3CF6B91E-C5F6-46A4-B036-72597274FCC0}"));
System.Security.Cryptography.Xml.DataObject officeObject = new System.Security.Cryptography.Xml.DataObject();
// do not change the order of the following two lines
officeObject.LoadXml(document.DocumentElement); // resets ID
officeObject.Id = OfficeObjectID; // required ID, do not change
return officeObject;
}
/********************************************************/
static X509Certificate2 GetCertificate()
{
X509Store certStore = new X509Store(StoreLocation.CurrentUser);
certStore.Open(OpenFlags.ReadOnly);
X509Certificate2Collection certs = X509Certificate2UI.SelectFromCollection(certStore.Certificates, "Select a certificate", "Please select a certificate",
X509SelectionFlag.SingleSelection);
return certs.Count > 0 ? certs[0] : null;
}
}
Program.cs
class Program
{
static void Main(string[] args)
{
Signature.DigiSign(#"D:\abc.docx");
}
}
And the file abc.docx after sign :
In the Additional Information of the signature , the system date/time(sign time) is diferrent from my local time and the date/time format too.I try to change my local time zone and reset date/time but it still not work.
What am i missing?

Use SecureBlackBox for .NET solve my problem !

C# asp.net CERTENROLLLib PKCS10 creation

I'm trying to create a keypair running the above code sample. I'm running this inside a activex. I have no problem to run this local, but when I install it on my server, it's not working properly, it only works if I run my IE as administrator.
System.UnauthorizedAccessException:
CertEnroll::CX509PrivateKey::Create: Access Denied. 0x80070005 (WIN32:
5)
em CERTENROLLLib.IX509PrivateKey.Create()
Any tips on how to run this without adm permission? Or there's any other way to create a key pair, send to CA and write the cert to a smartcard?
I'm following this code:
https://blogs.msdn.microsoft.com/alejacma/2008/09/05/how-to-create-a-certificate-request-with-certenroll-and-net-c/
public String CreateBase64KeyPair(string CN)
{
string msg = string.Empty;
try
{
CX509CertificateRequestPkcs10 objPkcs10 = (CX509CertificateRequestPkcs10)Activator.CreateInstance(Type.GetTypeFromProgID("X509Enrollment.CX509CertificateRequestPkcs10"));
IX509PrivateKey objPrivateKey = (IX509PrivateKey)Activator.CreateInstance(Type.GetTypeFromProgID("X509Enrollment.CX509PrivateKey"));
CCspInformation objCSP = (CCspInformation)Activator.CreateInstance(Type.GetTypeFromProgID("X509Enrollment.CCspInformation"));
CCspInformations objCSPs = (CCspInformations)Activator.CreateInstance(Type.GetTypeFromProgID("X509Enrollment.CCspInformations"));
CX500DistinguishedName objDN = (CX500DistinguishedName)Activator.CreateInstance(Type.GetTypeFromProgID("X509Enrollment.CX500DistinguishedName"));
CX509Enrollment objEnroll = (CX509Enrollment)Activator.CreateInstance(Type.GetTypeFromProgID("X509Enrollment.CX509Enrollment"));
CObjectIds objObjectIds = (CObjectIds)Activator.CreateInstance(Type.GetTypeFromProgID("X509Enrollment.CObjectIds"));
CObjectId objObjectId = (CObjectId)Activator.CreateInstance(Type.GetTypeFromProgID("X509Enrollment.CObjectId"));
CX509ExtensionKeyUsage objExtensionKeyUsage = (CX509ExtensionKeyUsage)Activator.CreateInstance(Type.GetTypeFromProgID("X509Enrollment.CX509ExtensionKeyUsage"));
CX509ExtensionEnhancedKeyUsage objX509ExtensionEnhancedKeyUsage = (CX509ExtensionEnhancedKeyUsage)Activator.CreateInstance(Type.GetTypeFromProgID("X509Enrollment.CX509ExtensionEnhancedKeyUsage"));
// Initialize the csp object using the desired Cryptograhic Service Provider (CSP)
objCSP.InitializeFromName(YPSIDCSP_NAME);
objCSP.GetDefaultSecurityDescriptor(true);
// Add this CSP object to the CSP collection object
objCSPs.Add(objCSP);
//Provide key container name, key length and key spec to the private key object
objPrivateKey.Length = 1024; //KEY_LEN_MY_DEFAULT
objPrivateKey.ProviderType = X509ProviderType.XCN_PROV_RSA_FULL; //XEnroll.ProviderType=1
objPrivateKey.KeySpec = X509KeySpec.XCN_AT_SIGNATURE; //XEnroll.KeySpec=AT_KEYEXCHANGE
objPrivateKey.KeyUsage = X509PrivateKeyUsageFlags.XCN_NCRYPT_ALLOW_ALL_USAGES;
objPrivateKey.ExportPolicy = X509PrivateKeyExportFlags.XCN_NCRYPT_ALLOW_EXPORT_FLAG;
objPrivateKey.MachineContext = false;
// Provide the CSP collection object (in this case containing only 1 CSP object) to the private key object
objPrivateKey.CspInformations = objCSPs;
// Create the actual key pair
objPrivateKey.Create();
// Initialize the PKCS#10 certificate request object based on the private key.
// Using the context, indicate that this is a user certificate request and don’t provide a template name
objPkcs10.InitializeFromPrivateKey(X509CertificateEnrollmentContext.ContextUser, objPrivateKey, string.Empty);
// Key Usage Extension
objExtensionKeyUsage.InitializeEncode(
CERTENROLLLib.X509KeyUsageFlags.XCN_CERT_DIGITAL_SIGNATURE_KEY_USAGE |
CERTENROLLLib.X509KeyUsageFlags.XCN_CERT_KEY_ENCIPHERMENT_KEY_USAGE |
CERTENROLLLib.X509KeyUsageFlags.XCN_CERT_DATA_ENCIPHERMENT_KEY_USAGE |
CERTENROLLLib.X509KeyUsageFlags.XCN_CERT_NON_REPUDIATION_KEY_USAGE
);
objPkcs10.X509Extensions.Add((CX509Extension)objExtensionKeyUsage);
// Enhanced Key Usage Extension
objObjectId.InitializeFromValue("1.3.6.1.5.5.7.3.2"); // OID for Client Authentication usage
objObjectIds.Add(objObjectId);
objX509ExtensionEnhancedKeyUsage.InitializeEncode(objObjectIds);
objPkcs10.X509Extensions.Add((CX509Extension)objX509ExtensionEnhancedKeyUsage);
// Encode the name in using the Distinguished Name object
objDN.Encode("CN=" + CN.Trim(), X500NameFlags.XCN_CERT_NAME_STR_NONE);
// Assing the subject name by using the Distinguished Name object initialized above
objPkcs10.Subject = objDN;
// Create enrollment request
objEnroll.InitializeFromRequest(objPkcs10);
return objEnroll.CreateRequest(EncodingType.XCN_CRYPT_STRING_BASE64);
}
catch (Exception ex)
{
return ex.ToString();
}
}

adding extensions to a certificate request ( password-challenge ) with C# and CertENrollLib

I have to add extensions to a certificate request ( CSR ) in such a way that I respect a given structure. Namely this one
On the left is the structure I must respect for the chalenge password, on the right the structure I get when I simply generate a OID object from the challenge-password OID value, then embedding all this directly into the extension list of the PKCS10 request:
CObjectId cp_oid = new CObjectId();
// OID 1.2.840.113549.1.9.7
// cp_oid.InitializeFromName(CERTENROLL_OBJECTID.XCN_OID_RSA_challengePwd);
cp_oid.InitializeFromValue("1.2.840.113549.1.9.7");
then I create a CX509Extension object add the OID to the PKCS10 request:
CX509Extension extension = new CX509Extension();
string b64__challengePassword=System.Convert.ToBase64String(System.Text.Encoding.UTF8.GetBytes(this.challengePassword));
extension.Initialize(cp_oid, EncodingType.XCN_CRYPT_STRING_BASE64_ANY, b64__challengePassword);
_certificateRequest.X509Extensions.Add(extension);
since the structure is clearly different from what I must obtain ( see the right part of the previous picture ) , I am now using a more sophisticated approach:
_certificateRequest = new CX509CertificateRequestPkcs10();
_certificateRequest.InitializeFromPrivateKey(X509CertificateEnrollmentContext.ContextUser, (CX509PrivateKey)_privateKey, null);
_certificateRequest.Subject = (CX500DistinguishedName)_subjectName;
CObjectIds cp_oids = new CObjectIds();
CObjectId cp_oid = new CObjectId();
// OID 1.2.840.113549.1.9.7
// cp_oid.InitializeFromName(CERTENROLL_OBJECTID.XCN_OID_RSA_challengePwd);
cp_oid.InitializeFromValue("1.2.840.113549.1.9.7");
CX509Extension _extension = new CX509Extension();
cp_oids.Add(cp_oid);
//now how do I add that oid list to the 1.2.840.113549.1.9.14 OID ?
//I try with CX509ExtensionEnhancedKeyUsage instead of a simple CX509Extension
//which one of all these is the correct extensions?
/*
* IX509ExtensionAlternativeNames Specifies one or more alternative name forms for the subject of a certificate.
IX509ExtensionAuthorityKeyIdentifier Represents an AuthorityKeyIdentifier extension.
IX509ExtensionBasicConstraints Specifies whether the certificate subject is a certification authority and, if so, the depth of the subordinate certification authority chain.
IX509ExtensionCertificatePolicies Represents a collection of policy information terms.
IX509ExtensionMSApplicationPolicies Represents a collection of object identifiers that indicate how a certificate can be used by an application.
IX509ExtensionEnhancedKeyUsage Represents a collection of object identifiers that identify the intended uses of the public key contained in a certificate.
IX509ExtensionKeyUsage Represents restrictions on the operations that can be performed by the public key contained in the certificate.
IX509Extensions Manages a collection of IX509Extension objects.
IX509ExtensionSmimeCapabilities Represents a collection that reports the decryption capabilities of an email recipient to an email sender.
IX509ExtensionSubjectKeyIdentifier Represents a SubjectKeyIdentifier extension used to identify a signing certificate.
IX509ExtensionTemplate Represents a CertificateTemplate extension that contains a version 2 template.
IX509ExtensionTemplateName Represents a CertificateTemplateName extension that contains a version 1 template.
*/
CX509ExtensionEnhancedKeyUsage eku = new CX509ExtensionEnhancedKeyUsage();
eku.InitializeEncode(cp_oids);
eku.Critical = false;
CX509AttributeExtensions InitExt = new CX509AttributeExtensions();
// Add the extension objects into an IX509Extensions collection.
CX509Extensions ext1 = new CX509Extensions();
ext1.Add((CX509Extension)eku);
// Use the IX509Extensions collection//to initialize an IX509AttributeExtensions object.
CX509AttributeExtensions ext1att = new CX509AttributeExtensions();
ext1att.InitializeEncode(ext1);
//Add the IX509AttributeExtensions object to an IX509Attributes collection.
CX509Attributes att1 = new CX509Attributes();
att1.Add((CX509Attribute)ext1att);
//Use the IX509Attributes collection to initialize an ICryptAttribute object.
CCryptAttribute crypt1 = new CCryptAttribute();
crypt1.InitializeFromValues(att1);
//Initialize a CMC or PKCS #10 request object and retrieve the ICryptAttributes collection.
//Add the ICryptAttribute object to the ICryptAttributes collection for the request.
_certificateRequest.CryptAttributes.Add(crypt1);
//Console.WriteLine("-- encode");
this.status2 = this.status2 + "-- encode <BR>";
try
{
_certificateRequest.Encode();
}
catch (Exception ex)
{
Console.WriteLine(ex.ToString());
}
string rawData = _certificateRequest.get_RawData();
Console.WriteLine("data=" + rawData);
However I get the puzzling error "The file exists. (Exception from HRESULT: 0x80070050)" at the end of the process when encoding the request , I tried with different smartcards ad the key containers are OK, not full.
Is my approach toward adding this challenge-password extension correct and how can I interpret this error?

The answer to the error you are getting "The file exists. (Exception from HRESULT: 0x80070050)" is because trying to set a key on a template that already has a key. just comment this:
CX509ExtensionEnhancedKeyUsage eku = new CX509ExtensionEnhancedKeyUsage();
eku.InitializeEncode(cp_oids);
eku.Critical = false;
CX509AttributeExtensions InitExt = new CX509AttributeExtensions();
// Add the extension objects into an IX509Extensions collection.
CX509Extensions ext1= new CX509Extensions();
ext1.Add((CX509Extension)eku);
and it should work.
search for this in the in the article Working with Active Directory Certificate Service via C# for:
Seems that we finished, but if we just execute it will throw an
exception to us, said that the file exists when adding some
extensions.
it explains everything.
from the article:
The exception message could be a little bit confusing. In fact this is
because we defined something which had been defined in the certificate
template. If we dig into the source code we can see that the exception
occurred when we added the key usage extension.
And if we get back to the CA server and open the template we are
using, we can find that the key usage had been defined in the
template. This means in the code, or in the certificate request we
should not specify it again.
Hence we need to comment the code for adding the key usage, also we
need to comment the enhanced key usage part since it had been defined
in the template, too. Because we let the request supply the subject
name so here we can still specify the subject information in the
request. The method for generating request message would be like this.

Below is code to include Challenge Password into PKCS10 generated by CertEnroll:
private static byte[] getDerBytes(int tag, byte[] data)
{
if (data.Length > byte.MaxValue)
{
throw new NotSupportedException("Support for integers greater than 255 not yet implemented.");
}
var header = new byte[] { (byte)tag, (byte)data.Length };
return header.Concat(data).ToArray();
}
and
public static byte[] EncodePrintableString(string data)
{
var dataBytes = Encoding.ASCII.GetBytes(data);
return getDerBytes(0x13, dataBytes);
}
and finnally:
CObjectId cp_oid = new CObjectId();
cp_oid.InitializeFromName(CERTENROLL_OBJECTID.XCN_OID_RSA_challengePwd);
byte[] b64__challengePassword = EncodePrintableString("password");
ICryptAttribute ChallengeAttributes = new CCryptAttribute();
ChallengeAttributes.InitializeFromObjectId(cp_oid);
CX509Attribute ChallengeAttribute = new CX509Attribute();
ChallengeAttribute.Initialize(cp_oid, EncodingType.XCN_CRYPT_STRING_BASE64_ANY,
Convert.ToBase64String(b64__challengePassword));
ChallengeAttributes.Values.Add(ChallengeAttribute);
objPkcs10.CryptAttributes.Add((CCryptAttribute)ChallengeAttributes);

C# How can I validate a Root-CA-Cert certificate (x509) chain?

Let's say I have three certificates (in Base64 format)
Root
|
--- CA
|
--- Cert (client/signing/whatever)
How can I validate the certs and certificate path/chain in C#?
(All those three certs may not be in my computer cert store)
Edit: BouncyCastle has the function to verify. But I'm trying not to use any third-party library.
byte[] b1 = Convert.FromBase64String(x509Str1);
byte[] b2 = Convert.FromBase64String(x509Str2);
X509Certificate cer1 =
new X509CertificateParser().ReadCertificate(b1);
X509Certificate cer2 =
new X509CertificateParser().ReadCertificate(b2);
cer1.Verify(cer2.GetPublicKey());
If the cer1 is not signed by cert2 (CA or root), there will be exception. This is exactly what I want.

The X509Chain class was designed to do this, you can even customize how it performs the chain building process.
static bool VerifyCertificate(byte[] primaryCertificate, IEnumerable<byte[]> additionalCertificates)
{
var chain = new X509Chain();
foreach (var cert in additionalCertificates.Select(x => new X509Certificate2(x)))
{
chain.ChainPolicy.ExtraStore.Add(cert);
}
// You can alter how the chain is built/validated.
chain.ChainPolicy.RevocationMode = X509RevocationMode.NoCheck;
chain.ChainPolicy.VerificationFlags = X509VerificationFlags.IgnoreWrongUsage;
// Do the validation.
var primaryCert = new X509Certificate2(primaryCertificate);
return chain.Build(primaryCert);
}
The X509Chain will contain additional information about the validation failure after Build() == false if you need it.
Edit: This will merely ensure that your CA's are valid. If you want to ensure that the chain is identical you can check the thumbprints manually. You can use the following method to ensure that the certification chain is correct, it expects the chain in the order: ..., INTERMEDIATE2, INTERMEDIATE1 (Signer of INTERMEDIATE2), CA (Signer of INTERMEDIATE1)
static bool VerifyCertificate(byte[] primaryCertificate, IEnumerable<byte[]> additionalCertificates)
{
var chain = new X509Chain();
foreach (var cert in additionalCertificates.Select(x => new X509Certificate2(x)))
{
chain.ChainPolicy.ExtraStore.Add(cert);
}
// You can alter how the chain is built/validated.
chain.ChainPolicy.RevocationMode = X509RevocationMode.NoCheck;
chain.ChainPolicy.VerificationFlags = X509VerificationFlags.IgnoreWrongUsage;
// Do the preliminary validation.
var primaryCert = new X509Certificate2(primaryCertificate);
if (!chain.Build(primaryCert))
return false;
// Make sure we have the same number of elements.
if (chain.ChainElements.Count != chain.ChainPolicy.ExtraStore.Count + 1)
return false;
// Make sure all the thumbprints of the CAs match up.
// The first one should be 'primaryCert', leading up to the root CA.
for (var i = 1; i < chain.ChainElements.Count; i++)
{
if (chain.ChainElements[i].Certificate.Thumbprint != chain.ChainPolicy.ExtraStore[i - 1].Thumbprint)
return false;
}
return true;
}
I am unable to test this because I don't have a full CA chain with me, so it would be best to debug and step through the code.

The X509Chain does not work reliably for scenarios where you do not have the root certificate in the trusted CA store on the machine.
Others will advocate using bouncy castle. I wanted to avoid bringing in another library just for this task, so I wrote my own.
As see in RFC3280 Section 4.1 the certificate is a ASN1 encoded structure, and at it's base level is comprised of only 3 elements.
The "TBS" (to be signed) certificate
The signature algorithm
and the signature value
Certificate ::= SEQUENCE {
tbsCertificate TBSCertificate,
signatureAlgorithm AlgorithmIdentifier,
signatureValue BIT STRING
}
C# actually has a handy tool for parsing ASN1, the System.Formats.Asn1.AsnDecoder.
Using this, we can extract these 3 elements from the certificate to verify the chain.
The first step was extracting the certificate signature, since the X509Certificate2 class does not expose this information and it is necessary for the purpose of certificate validation.
Example code to extract the signature value part:
public static byte[] Signature(
this X509Certificate2 certificate,
AsnEncodingRules encodingRules = AsnEncodingRules.BER)
{
var signedData = certificate.RawDataMemory;
AsnDecoder.ReadSequence(
signedData.Span,
encodingRules,
out var offset,
out var length,
out _
);
var certificateSpan = signedData.Span[offset..(offset + length)];
AsnDecoder.ReadSequence(
certificateSpan,
encodingRules,
out var tbsOffset,
out var tbsLength,
out _
);
var offsetSpan = certificateSpan[(tbsOffset + tbsLength)..];
AsnDecoder.ReadSequence(
offsetSpan,
encodingRules,
out var algOffset,
out var algLength,
out _
);
return AsnDecoder.ReadBitString(
offsetSpan[(algOffset + algLength)..],
encodingRules,
out _,
out _
);
}
The next step is to extract the TBS certificate. This is the original data which was signed.
example code to extract the TBS certificate data:
public static ReadOnlySpan<byte> TbsCertificate(
this X509Certificate2 certificate,
AsnEncodingRules encodingRules = AsnEncodingRules.BER)
{
var signedData = certificate.RawDataMemory;
AsnDecoder.ReadSequence(
signedData.Span,
encodingRules,
out var offset,
out var length,
out _
);
var certificateSpan = signedData.Span[offset..(offset + length)];
AsnDecoder.ReadSequence(
certificateSpan,
encodingRules,
out var tbsOffset,
out var tbsLength,
out _
);
// include ASN1 4 byte header to get WHOLE TBS Cert
return certificateSpan.Slice(tbsOffset - 4, tbsLength + 4);
}
You may notice that when extracting the TBS certiifcate I needed to include the ASN1 header in the data, this is because the signature of the TBS Certificate INCLUDES this data (this annoyed me for a while).
For the first time in history, the Microsoft does not impede us with their API design, and we are able to obtain the Signature Algorithm directly from the X509Certificate2 object. Then we just need to decide to what extend we are going to implement different hash algorithms.
var signature = signed.Signature();
var tbs = signed.TbsCertificate();
var alg = signed.SignatureAlgorithm;
// https://learn.microsoft.com/en-us/openspecs/windows_protocols/ms-gpnap/a48b02b2-2a10-4eb0-bed4-1807a6d2f5ad
switch (alg)
{
case { Value: var value } when value?.StartsWith("1.2.840.113549.1.1.") ?? false:
return signedBy.GetRSAPublicKey()?.VerifyData(
tbs,
signature,
value switch {
"1.2.840.113549.1.1.11" => HashAlgorithmName.SHA256,
"1.2.840.113549.1.1.12" => HashAlgorithmName.SHA384,
"1.2.840.113549.1.1.13" => HashAlgorithmName.SHA512,
_ => throw new UnsupportedSignatureAlgorithm(alg)
},
RSASignaturePadding.Pkcs1
) ?? false;
case { Value: var value } when value?.StartsWith("1.2.840.10045.4.3.") ?? false:
return signedBy.GetECDsaPublicKey()?.VerifyData(
tbs,
signature,
value switch
{
"1.2.840.10045.4.3.2" => HashAlgorithmName.SHA256,
"1.2.840.10045.4.3.3" => HashAlgorithmName.SHA384,
"1.2.840.10045.4.3.4" => HashAlgorithmName.SHA512,
_ => throw new UnsupportedSignatureAlgorithm(alg)
},
DSASignatureFormat.Rfc3279DerSequence
) ?? false;
default: throw new UnsupportedSignatureAlgorithm(alg);
}
As shown in the code above, https://learn.microsoft.com/en-us/openspecs/windows_protocols/ms-gpnap/a48b02b2-2a10-4eb0-bed4-1807a6d2f5ad is a good resource to see the mapping of algorithms and OIDs.
Another thing you should be aware of is that there are some articles out there that claim that for elliptical curve algorithms, microsoft expects a R,S formatted key instead of a DER formatted key. I tried to convert the key to this format but it ultimately didn't work. What I discovered was that it was necessary to use the DSASignatureFormat.Rfc3279DerSequence parameter.
Additional certificate checks, like "not before" and "not after", or CRL and OCSP checks can be done in addition to the chain verification.