var secureRandom = new SecureRandom();
ECPrivateKeyParameters prk = (ECPrivateKeyParameters)ReadPemObject("prk.pem");
ECPublicKeyParameters pbk = (ECPublicKeyParameters)ReadPemObject("pbk.pem");
X509ExtensionsGenerator extGen = new X509ExtensionsGenerator();
extGen.AddExtension(X509Extensions.KeyUsage, true, new KeyUsage(240));
extGen.AddExtension(new DerObjectIdentifier("2.5.29.37"), false, new DerSequence(new DerObjectIdentifier("1.3.6.1.5.5.7.3.2")));
var subjectPbkInfo = new SubjectPublicKeyInfo(new AlgorithmIdentifier(RosstandartObjectIdentifiers.id_tc26_signwithdigest_gost_3410_12_256.Id), pbk.Q.GetEncoded());
var subjectKeyID = new SubjectKeyIdentifier(subjectPbkInfo);
extGen.AddExtension(new DerObjectIdentifier("2.5.29.14"), false, new DerOctetString(subjectKeyID.GetKeyIdentifier()));
AttributePkcs attributePkcs = new AttributePkcs(PkcsObjectIdentifiers.Pkcs9AtExtensionRequest, new DerSet(extGen.Generate()));
var request = new Pkcs10CertificationRequest(
    "1.2.643.7.1.1.3.2",
    new X509Name("CN=Anatolka"),
    (ECPublicKeyParameters)pbk,
    new DerSet(attributePkcs),
    (ECPrivateKeyParameters)prk);

static System.Object ReadPemObject (String _fileName)
{
    TextReader TextReader = File.OpenText($".\\{_fileName}");
    var PemReader = new PemReader(TextReader);
    var _object = PemReader.ReadObject();
    TextReader.Close();
    TextReader.Dispose();
    return _object;
}