PnPeople.Security

NuGet Package

SEED Cryptography Algorithm Library for .NET Standard 2.0+

How to use

You can use this library to convert your SEED encrypted private key into a .NET standard RSA instance.

1. First read the .der file and the .key file respectively into a byte array.
2. Create an instance of the System.Security.Cryptography.X509Certificates.X509Certificate2 class to read the public key data.
3. Call the GetPrivateKeyInfo function of the PnPeople.Security.CertPrivateKeyHelper class to read the private key data.
4. Prepare the certificate password by inputting it from the user.
5. Call the GetPrivateKeyDecryptor function of the PnPeople.Security.CertPrivateKeyHelper class to obtain exact private key decryptor.
6. When calling the decryptor delegate function, pass the private key information data and certificate password. The decryptor will return a standard RSA provider instance in .NET.

Now you can use the RSA provider instance to sign the data.

Sample Code

Here is the sample application code.

var folder = Path.Combine(
    Environment.GetEnvironmentVariable("USERPROFILE"),
    "AppData", "LocalLow", "NPKI");

foreach (var eachProviderDirectory in Directory.GetDirectories(folder))
{
    Console.WriteLine($"[{Path.GetFileName(eachProviderDirectory)}]");

    foreach (var eachDirectory in Directory.GetDirectories(Path.Combine(eachProviderDirectory, "USER")))
    {
        Console.WriteLine($"{Path.GetFileName(eachDirectory)}");
        var certFile = Directory.GetFiles(eachDirectory, "*.der", SearchOption.TopDirectoryOnly).FirstOrDefault();

        X509Certificate2 token = null;

        if (certFile != null && File.Exists(certFile))
        {
            token = new X509Certificate2(X509Certificate.CreateFromCertFile(certFile));

            Console.WriteLine("- IssuerName: " + token.Issuer);
            Console.WriteLine("- KeyAlgorithm: " + token.GetKeyAlgorithm());
            Console.WriteLine("- KeyAlgorithmParameters: " + token.GetKeyAlgorithmParametersString());
            Console.WriteLine("- Name: " + token.Subject);
            Console.WriteLine("- PublicKey: " + token.GetPublicKeyString());
            Console.WriteLine("- SerialNumber: " + token.GetSerialNumberString());
            Console.WriteLine("- HasPrivateKey: " + token.HasPrivateKey);

            var currentDateTime = DateTime.Now;
            if (currentDateTime <= token.NotBefore)
            {
                Console.WriteLine("- Certificate is not valid yet.");
                continue;
            }
            else if (token.NotAfter <= currentDateTime)
            {
                Console.WriteLine("- Certificate has expiered.");
                continue;
            }
        }

        var keyFile = Directory.GetFiles(eachDirectory, "*.key", SearchOption.TopDirectoryOnly).FirstOrDefault();

        if (keyFile == null || !File.Exists(keyFile))
            continue;

        var bytes = File.ReadAllBytes(keyFile);
        var privKeyInfo = CertPrivateKeyHelper.GetPrivateKeyInfo(bytes);
        Console.WriteLine("- KeyType: " + privKeyInfo.KeyType);
        Console.WriteLine("- Algorithm: " + privKeyInfo.Algorithm);

        Console.Write("- Type private key password: ");
        var passwd = ReadPasswordFromConsole();

        var copiedPassword = CertPrivateKeyHelper.CopyFromSecureString(passwd);
        var decryptor = CertPrivateKeyHelper.GetPrivateKeyDecryptor(privKeyInfo);

        if (decryptor == null)
        {
            Console.WriteLine("- Unsupported algorithm found.");
            continue;
        }

        var provider = decryptor.Invoke(privKeyInfo, copiedPassword);

        if (provider != null)
        {
            var randomString = string.Concat(Enumerable.Range(1, (int)(Math.Abs(DateTime.Now.Ticks) % 9)).Select(x => Guid.NewGuid().ToString("n")));
            var buffer = Encoding.Default.GetBytes(randomString);
            var signed = provider.SignData(buffer, HashAlgorithmName.SHA1, RSASignaturePadding.Pkcs1);
            var result = provider.VerifyData(buffer, signed, HashAlgorithmName.SHA1, RSASignaturePadding.Pkcs1);

            Console.WriteLine($"- Signature Validation Result: {(result ? "Valid" : "Invalid")}");

            if (result && token != null)
            {
                var tokenWithPrivateKey = token.CopyWithPrivateKey(provider);
                var directoryPath = Path.GetDirectoryName(certFile);

                var pfxData = tokenWithPrivateKey.Export(X509ContentType.Pfx, passwd);
                var pfxPath = Path.Combine(directoryPath, "signCertNew.pfx");
                File.WriteAllBytes(pfxPath, pfxData);

                if (File.Exists(pfxPath))
                    Console.WriteLine($"- PFX Converted: {pfxPath}");

                // Separate PFX back into DER/KEY (but don't use SEED encryption)
                tokenWithPrivateKey = new X509Certificate2(File.ReadAllBytes(pfxPath), passwd, X509KeyStorageFlags.Exportable);

                var certData = tokenWithPrivateKey.Export(X509ContentType.Cert);
                var certPath = Path.Combine(directoryPath, "signCertNew.der");
                File.WriteAllBytes(certPath, certData);

                if (File.Exists(certPath))
                    Console.WriteLine($"- Certificate converted: {certPath}");

                // https://www.rootca.or.kr/kcac/down/Guide/Implementation_Guideline_for_Safe_Usage_of_Accredited_Certificate_using_bio_information_in_Smart_phone.pdf
                // According to the contents of '2.2 Authenticated Certificate Digital Signature Creation Information Storage Plan' of the above document, IterationCount seems to be promised to 2048.
                var keyData = tokenWithPrivateKey.PrivateKey.ExportEncryptedPkcs8PrivateKey(
                    copiedPassword,
                    new PbeParameters(PbeEncryptionAlgorithm.TripleDes3KeyPkcs12, HashAlgorithmName.SHA1, 2048));

                var keyPath = Path.Combine(directoryPath, "signPriNew.key");
                File.WriteAllBytes(keyPath, keyData);

                if (File.Exists(keyPath))
                    Console.WriteLine($"- Private key converted: {keyPath}");
            }
        }
        else
        {
            Console.WriteLine($"- Cannot decrypt private key");
        }
    }
}

License

This project is licensed under the MIT License.

Original Source Code Excerpted From:

• https://thermidor.tistory.com/430
• https://thermidor.tistory.com/431
• Mono.Security