iTextSharp 5.5.6: Signature invalid with SwissSign USB token - itext

Question

I read Bruno Lowagie's white paper: Digital Signatures for PDF documents.
I followed the examples and I was able to sign PDF's with my SwissSign USB token using MSCAPI. This line of code does the trick:
MakeSignature.SignDetached(appearance, pks, chain, crlList, ocspClient, tsaClient, estimatedSize, subfilter);
I am also passing the TSA client with the SwissSign TSA URL: tsa(dot)swisssign(dot)net
When I open the signed PDF in Acrobat Reader DC 2015, I get the error:
Signature is invalid.
There are errors in the formatting or information contained in this signature
Signer's identity has not yet been verified
Signing time is from the clock on the signer's computer.
When signing the PDF with the SwissSign tool everything looks fine: signature is valid.
I have put the PDF's here:
invalid PDF - signed with iTextSharp 5.5.6
valid PDF - signed with SwissSign tool
I have tried different combinations of hash algorithms, but without success. What am I missing?
Any help appreciated.
Best Regards,
Phil
Here is the full code:
private void _sign_Click(object sender, RoutedEventArgs e)
{
X509Store x509Store = new X509Store(StoreName.My, StoreLocation.CurrentUser);
x509Store.Open(OpenFlags.ReadOnly);
X509Certificate2Collection certificates = x509Store.Certificates;
IList<Org.BouncyCastle.X509.X509Certificate> chain = new List<Org.BouncyCastle.X509.X509Certificate>();
X509Certificate2 pk = null;
if (certificates.Count > 0)
{
for (int i = 0; i < certificates.Count; i++)
{
if (certificates[i].FriendlyName == "Philipp Egger (Qualified Signature) .....") // Phil Egger Signature Certificate
{
pk = certificates[i];
break;
}
}
X509Chain x509chain = new X509Chain();
x509chain.Build(pk);
foreach (X509ChainElement x509ChainElement in x509chain.ChainElements)
{
chain.Add(Org.BouncyCastle.Security.DotNetUtilities.FromX509Certificate(x509ChainElement.Certificate));
}
}
x509Store.Close();
if (pk != null)
{
#region connect usb token
///////////////////
RSACryptoServiceProvider rsa = (RSACryptoServiceProvider)pk.PrivateKey;
CspParameters cspp = new CspParameters();
cspp.KeyContainerName = rsa.CspKeyContainerInfo.KeyContainerName;
cspp.ProviderName = rsa.CspKeyContainerInfo.ProviderName;
cspp.ProviderType = rsa.CspKeyContainerInfo.ProviderType;
cspp.Flags = CspProviderFlags.NoPrompt;
System.Security.SecureString pwstr = new System.Security.SecureString();
pwstr.AppendChar('x');
pwstr.AppendChar('x');
pwstr.AppendChar('x');
cspp.KeyPassword = pwstr;
RSACryptoServiceProvider rsa2 = new RSACryptoServiceProvider(cspp);
rsa2.PersistKeyInCsp = true;
// PIN is cached from now on and popup won't appear
///////////////////////
#endregion
IOcspClient ocspClient = new OcspClientBouncyCastle();
ITSAClient tsaClient = null;
for (int i = 0; i < chain.Count; i++)
{
Org.BouncyCastle.X509.X509Certificate cert = chain[i];
String tsaUrl = CertificateUtil.GetTSAURL(cert);
if (tsaUrl != null)
{
tsaClient = new TSAClientBouncyCastle(tsaUrl);
break;
}
}
if (tsaClient == null)
{
tsaClient = new TSAClientBouncyCastle("http://tsa.swisssign.net");
//tsaClient = new MyTSAClientBouncyCastle("http://tsa.swisssign.net"); // set user-agent
}
IList<ICrlClient> crlList = new List<ICrlClient>();
crlList.Add(new CrlClientOnline(chain));
string pathSource = #"C:\Temp\test_to_sign.pdf";
string pathTarget3 = #"C:\Temp\test_to_sign-signed3.pdf";
// this.SignNew(pathSource, pathTarget1, chain, pk, DigestAlgorithms.SHA1, CryptoStandard.CMS, "Test", "Rheinau", crlList, ocspClient, tsaClient, 0);
// this.SignNew(pathSource, pathTarget2, chain, pk, DigestAlgorithms.SHA1, CryptoStandard.CADES, "Test", "Rheinau", crlList, ocspClient, tsaClient, 0);
this.SignNew(pathSource, pathTarget3, chain, pk, DigestAlgorithms.SHA256, CryptoStandard.CMS, "Test", "Rheinau", crlList, ocspClient, tsaClient, 0);
// this.SignNew(pathSource, pathTarget4, chain, pk, DigestAlgorithms.SHA256, CryptoStandard.CADES, "Test", "Rheinau", crlList, ocspClient, tsaClient, 0);
// this.SignNew(pathSource, pathTarget5, chain, pk, DigestAlgorithms.SHA384, CryptoStandard.CMS, "Test", "Rheinau", crlList, ocspClient, tsaClient, 0);
// this.SignNew(pathSource, pathTarget6, chain, pk, DigestAlgorithms.SHA384, CryptoStandard.CADES, "Test", "Rheinau", crlList, ocspClient, tsaClient, 0);
// this.SignNew(pathSource, pathTarget7, chain, pk, DigestAlgorithms.SHA512, CryptoStandard.CMS, "Test", "Rheinau", crlList, ocspClient, tsaClient, 0);
// this.SignNew(pathSource, pathTarget8, chain, pk, DigestAlgorithms.SHA512, CryptoStandard.CADES, "Test", "Rheinau", crlList, ocspClient, tsaClient, 0);
this._txt.Text = "Signed successfully.";
}
else
{
this._txt.Text = "Certificate not found.";
}
}
public void SignNew(String src, String dest,
ICollection<Org.BouncyCastle.X509.X509Certificate> chain, X509Certificate2 pk,
String digestAlgorithm, CryptoStandard subfilter,
String reason, String location,
ICollection<ICrlClient> crlList,
IOcspClient ocspClient,
ITSAClient tsaClient,
int estimatedSize)
{
// Creating the reader and the stamper
PdfReader reader = null;
PdfStamper stamper = null;
FileStream os = null;
try
{
reader = new PdfReader(src);
os = new FileStream(dest, FileMode.Create);
stamper = PdfStamper.CreateSignature(reader, os, '\0');
// Creating the appearance
PdfSignatureAppearance appearance = stamper.SignatureAppearance;
appearance.Reason = reason;
appearance.Location = location;
appearance.SetVisibleSignature(new iTextSharp.text.Rectangle(36, 748, 144, 780), 1, "Signature1");
// Creating the signature
IExternalSignature pks = new X509Certificate2Signature(pk, digestAlgorithm);
MakeSignature.SignDetached(appearance, pks, chain, crlList, ocspClient, tsaClient, estimatedSize, subfilter);
}
catch (Exception e)
{
this._txt.Text = e.Message;
}
finally
{
if (reader != null)
reader.Close();
if (stamper != null)
stamper.Close();
if (os != null)
os.Close();
}
}

Answer 1

The problem is that it's apparently the SwissSign CSP (cryptographic service provider; a layer that provides a bridge between the Windows system stores and the hardware device) which picks the wrong private key when using MSCAPI.
There seems no workaround to pick the correct private key in MSCAPI.
Therefore, I decided to use PKCS11 and NCryptroki library. Here the code:
using Cryptware.NCryptoki;
using iTextSharp.text;
using iTextSharp.text.log;
using iTextSharp.text.pdf;
using iTextSharp.text.pdf.security;
using Org.BouncyCastle.Security;
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Security.Cryptography.X509Certificates;
using System.Text;
using System.Threading.Tasks;
namespace _07SignWithPKCS11DLL
{
class Program
{
static void Main(string[] args)
{
LoggerFactory.GetInstance().SetLogger(new SysoLogger());
// Creates a Cryptoki object related to the specific PKCS#11 native library
Cryptoki cryptoki = new Cryptoki("cvP11.dll");
cryptoki.Initialize();
// Reads the set of slots containing a token
SlotList slots = cryptoki.Slots;
if (slots.Count == 0)
{
Console.WriteLine("No slot available");
Console.ReadLine();
return;
}
// Gets the first slot available
Slot slot = slots[0];
if (!slot.IsTokenPresent)
{
Console.WriteLine("No token inserted in the slot: " + slots[0].Info.Description);
Console.ReadLine();
return;
}
// Gets the first token available
Token token = slot.Token;
// Opens a read serial session
Session session = token.OpenSession(Session.CKF_SERIAL_SESSION, null, null);
// Executes the login passing the user PIN
int nRes = session.Login(Session.CKU_USER, "secret");
if (nRes != 0)
{
Console.WriteLine("Wrong PIN");
return;
}
CSignWithPKCS11SC.Smartcardsign(session, "PhilippEggerQualifiedSignature", "SwissSign_nonRep ");
/*
CryptokiCollection template = new CryptokiCollection();
template.Add(new ObjectAttribute(ObjectAttribute.CKA_CLASS, CryptokiObject.CKO_CERTIFICATE));
template.Add(new ObjectAttribute(ObjectAttribute.CKA_CERTIFICATE_TYPE, Certificate.CKC_X_509));
CryptokiCollection objects = session.Objects.Find(template, 10);
// If the private keys is found continue
if (objects.Count > 0)
{
foreach (Object obj in objects)
{
Cryptware.NCryptoki.X509Certificate cert = (Cryptware.NCryptoki.X509Certificate)obj;
Console.WriteLine(cert.Label + " - " + cert.ID);
}
}
*/
// Logouts and closes the session
session.Logout();
session.Close();
cryptoki.Finalize(IntPtr.Zero);
Console.ReadLine();
}
}
class CryptokiPrivateKeySignature : IExternalSignature
{
private readonly Cryptware.NCryptoki.Session session;
RSAPrivateKey privateKey;
public CryptokiPrivateKeySignature(Session session, String alias)
{
this.session = session;
CryptokiCollection template = new CryptokiCollection();
template.Add(new ObjectAttribute(ObjectAttribute.CKA_CLASS, CryptokiObject.CKO_PRIVATE_KEY));
template.Add(new ObjectAttribute(ObjectAttribute.CKA_KEY_TYPE, Key.CKK_RSA));
// "SwissSign_nonRep "
// "SwissSign_digSig "
template.Add(new ObjectAttribute(ObjectAttribute.CKA_LABEL, alias));
/*
CryptokiCollection objects = session.Objects.Find(template, 10);
if (objects.Count > 0)
{
foreach (Object obj in objects)
{
RSAPrivateKey cert = (RSAPrivateKey)obj;
Console.WriteLine(cert.Label);
}
}
*/
privateKey = (RSAPrivateKey)session.Objects.Find(template);
}
public String GetHashAlgorithm()
{
return "SHA1";
}
public String GetEncryptionAlgorithm()
{
return "RSA";
}
public byte[] Sign(byte[] message)
{
session.SignInit(Mechanism.SHA1_RSA_PKCS, privateKey);
return session.Sign(message);
}
}
class CSignWithPKCS11SC
{
public const String SRC = #"C:\Temp\test_to_sign.pdf";
public const String DEST = #"C:\Temp\test_to_sign-pkcs11.pdf";
//public const String DLL = "c:/windows/system32/beidpkcs11.dll";
public const String DLL = "c:/windows/system32/cvP11.dll";
public void Sign(String src, String dest, ICollection<Org.BouncyCastle.X509.X509Certificate> chain, Session session, String alias,
String digestAlgorithm, CryptoStandard subfilter, String reason, String location,
ICollection<ICrlClient> crlList, IOcspClient ocspClient, ITSAClient tsaClient, int estimatedSize)
{
// Creating the reader and the stamper
PdfReader reader = null;
PdfStamper stamper = null;
FileStream os = null;
try
{
reader = new PdfReader(src);
os = new FileStream(dest, FileMode.Create);
stamper = PdfStamper.CreateSignature(reader, os, '\0');
// Creating the appearance
PdfSignatureAppearance appearance = stamper.SignatureAppearance;
appearance.Reason = reason;
appearance.Location = location;
appearance.SetVisibleSignature(new Rectangle(36, 748, 144, 780), 1, "sig");
// Creating the signature
IExternalSignature pks = new CryptokiPrivateKeySignature(session, alias);
MakeSignature.SignDetached(appearance, pks, chain, crlList, ocspClient, tsaClient, estimatedSize, subfilter);
}
finally
{
if (reader != null)
reader.Close();
if (stamper != null)
stamper.Close();
if (os != null)
os.Close();
}
}
public static void Smartcardsign(Session session, String alias, String aliasPrivateKey)
{
// Searchs for an RSA certificate object
// Sets the template with its attributes
CryptokiCollection template = new CryptokiCollection();
template.Add(new ObjectAttribute(ObjectAttribute.CKA_CLASS, CryptokiObject.CKO_CERTIFICATE));
template.Add(new ObjectAttribute(ObjectAttribute.CKA_CERTIFICATE_TYPE, Certificate.CKC_X_509));
template.Add(new ObjectAttribute(ObjectAttribute.CKA_LABEL, alias));
Cryptware.NCryptoki.X509Certificate nCert = (Cryptware.NCryptoki.X509Certificate)session.Objects.Find(template);
if (nCert != null)
{
X509Certificate2 cert = Utils.ConvertCertificate(nCert);
ICollection<Org.BouncyCastle.X509.X509Certificate> chain = new List<Org.BouncyCastle.X509.X509Certificate>();
X509Chain x509chain = new X509Chain();
x509chain.Build(cert);
foreach (X509ChainElement x509ChainElement in x509chain.ChainElements)
{
chain.Add(DotNetUtilities.FromX509Certificate(x509ChainElement.Certificate));
}
IOcspClient ocspClient = new OcspClientBouncyCastle();
List<ICrlClient> crlList = new List<ICrlClient>();
crlList.Add(new CrlClientOnline(chain));
TSAClientBouncyCastle tsaClient = new TSAClientBouncyCastle("http://tsa.swisssign.net");
CSignWithPKCS11SC app = new CSignWithPKCS11SC();
Console.WriteLine("Logged in? " + session.IsLoggedIn);
app.Sign(SRC, DEST, chain, session, aliasPrivateKey, DigestAlgorithms.SHA256, CryptoStandard.CMS,
"Test", "Rheinau", crlList, ocspClient, tsaClient, 0);
}
else
{
Console.WriteLine("Certificate not found: " + alias);
}
}
}
}