Namespace: WvdS.System.Security.Cryptography.Signatures

Drop-in replacement extensions for digital signatures with Post-Quantum support. Extends RSA, ECDsa and X509Certificate2 with PQ-hybrid signing functions.

This class provides three types of signatures:

using var rsa = RSA.Create(2048);
byte[] data = Encoding.UTF8.GetBytes("Important data");
 
// Sign with explicit mode
byte[] signature = rsa.SignData(
    data,
    HashAlgorithmName.SHA256,
    RSASignaturePadding.Pkcs1,
    CryptoMode.Hybrid);
 
// Verify
bool isValid = rsa.VerifyData(
    data,
    signature,
    HashAlgorithmName.SHA256,
    RSASignaturePadding.Pkcs1,
    CryptoMode.Hybrid);

using var fileStream = File.OpenRead("document.pdf");
 
byte[] signature = rsa.SignData(
    fileStream,
    HashAlgorithmName.SHA256,
    RSASignaturePadding.Pkcs1,
    CryptoMode.Hybrid);

using var ecdsa = ECDsa.Create(ECCurve.NamedCurves.nistP256);
byte[] data = GetDataToSign();
 
// Sign
byte[] signature = ecdsa.SignData(
    data,
    HashAlgorithmName.SHA256,
    CryptoMode.Hybrid);
 
// Verify
bool isValid = ecdsa.VerifyData(
    data,
    signature,
    HashAlgorithmName.SHA256,
    CryptoMode.Hybrid);

var certificate = GetSigningCertificate();
byte[] data = GetDataToSign();
 
// Sign (automatically uses RSA or ECDSA)
byte[] signature = certificate.SignData(
    data,
    HashAlgorithmName.SHA256,
    CryptoMode.Hybrid);
 
// Verify
bool isValid = certificate.VerifyData(
    data,
    signature,
    HashAlgorithmName.SHA256,
    CryptoMode.Hybrid);

The key type is automatically detected:

• RSA certificate → RSA.SignData + ML-DSA
• ECDSA certificate → ECDsa.SignData + ML-DSA

Direct ML-DSA signatures without classical key:

// Generate key pair
var (publicKey, privateKey) = SignatureExtensions.GenerateMlDsaKeyPair();
 
// Sign
byte[] data = GetDataToSign();
byte[] signature = SignatureExtensions.SignMlDsa(data, privateKey);
 
// Verify
bool isValid = SignatureExtensions.VerifyMlDsa(data, signature, publicKey);

+---------------------------------------------+
| [4 Bytes] Classical signature length        |
| [n Bytes] Classical signature (RSA/ECDSA)   |
| [m Bytes] PQ signature (ML-DSA-65)          |
+---------------------------------------------+

For standalone signatures (without certificate), thread-local transient keys are used:

// Set own keys
var (pubKey, privKey) = SignatureExtensions.GenerateMlDsaKeyPair();
SignatureExtensions.SetTransientPqKey(pubKey, privKey);
 
// Now SignData/VerifyData can be used without certificate
byte[] sig = rsa.SignData(data, HashAlgorithmName.SHA256,
    RSASignaturePadding.Pkcs1, CryptoMode.Hybrid);
 
// Only public key for verification
SignatureExtensions.SetTransientPqPublicKey(pubKey);
bool valid = rsa.VerifyData(data, sig, HashAlgorithmName.SHA256,
    RSASignaturePadding.Pkcs1, CryptoMode.Hybrid);
 
// Cleanup (overwrites private key with zeros)
SignatureExtensions.ClearTransientPqKey();

// 1. Configure CryptoMode
CryptoConfig.DefaultMode = CryptoMode.Hybrid;
 
// 2. Load certificate (with PQ keys)
var cert = X509Certificate2ExportExtensions.ImportPfx(
    "signing-cert.pfx",
    "password");
 
// 3. Sign document
byte[] documentData = File.ReadAllBytes("contract.pdf");
byte[] signature = cert.SignData(documentData, HashAlgorithmName.SHA256);
 
// 4. Save signature
File.WriteAllBytes("contract.sig", signature);
 
// 5. Verify later
var verifyCert = new X509Certificate2("signing-cert.cer");
bool isValid = verifyCert.VerifyData(
    File.ReadAllBytes("contract.pdf"),
    File.ReadAllBytes("contract.sig"),
    HashAlgorithmName.SHA256);
 
Console.WriteLine($"Signature valid: {isValid}");

• Signatures Namespace
• SignedDataExtensions
• X509Certificate2Extensions
• ML-DSA Algorithm

Wolfgang van der Stille @ EMSR DATA d.o.o. - Post-Quantum Cryptography Professional