murmur/Cert: remove auto-generation of Diffie-Hellman parameters.

Remove automatic generation of Diffie-Hellman parameters for vservers.

There were various problems with this approach.

 - It was somewhat slow.
 - To avoid blocking the main thread while generating the DH parameters,
   the code would enter an event loop. However, this meant that other code
   could still execute (for example, clients could connect to the server
   before the DH params were generated).

As a replacement, we're going to be shipping the Diffie-Hellman parameters
from RFC 7919 bundled into Murmur, and we'll default to one of them.

src/murmur/Cert.cpp

@@ -9,33 +9,6 @@
 #include "Server.h"
 #include "SelfSignedCertificate.h"
 
-#if defined(USE_QSSLDIFFIEHELLMANPARAMETERS)
-static BN_GENCB *mumble_BN_GENCB_new() {
-#if OPENSSL_VERSION_NUMBER >= 0x10100000L
-	return BN_GENCB_new();
-#else
-	return reinterpret_cast<BN_GENCB *>(malloc(sizeof(BN_GENCB)));
-#endif
-}
-
-static void mumble_BN_GENCB_free(BN_GENCB *cb) {
-#if OPENSSL_VERSION_NUMBER >= 0x10100000L
-	BN_GENCB_free(cb);
-#else
-	free(cb);
-#endif
-}
-
-// dh_progress is a status callback for DH_generate_parameters_ex.
-// We use it to run the event loop while generating DH params, in
-// order to keep the Murmur GUI on Windows responsive during the
-// process.
-static int dh_progress(int, int, BN_GENCB *) {
-	qApp->processEvents();
-	return 1;
-}
-#endif
-
 bool Server::isKeyForCert(const QSslKey &key, const QSslCertificate &cert) {
 	if (key.isNull() || cert.isNull() || (key.type() != QSsl::PrivateKey))
 		return false;
@@ -202,52 +175,6 @@ void Server::initializeCert() {
 		}
 	}
 
-#if defined(USE_QSSLDIFFIEHELLMANPARAMETERS)
-	if (qsdhpDHParams.isEmpty()) {
-		log("Generating new server 2048-bit Diffie-Hellman parameters. This could take a while...");
-
-		DH *dh = DH_new();
-		if (dh == NULL) {
-			qFatal("DH_new failed: unable to generate Diffie-Hellman parameters for virtual server");
-		}
-
-		// Generate DH params.
-		// We register a status callback in order to update the UI
-		// for Murmur on Windows. We don't show the actual status,
-		// but we do it to keep Murmur on Windows responsive while
-		// generating the parameters.
-		BN_GENCB *cb = mumble_BN_GENCB_new();
-		BN_GENCB_set(cb, dh_progress, NULL);
-		if (DH_generate_parameters_ex(dh, 2048, 2, cb) == 0) {
-			qFatal("DH_generate_parameters_ex failed: unable to generate Diffie-Hellman parameters for virtual server");
-		}
-
-		BIO *mem = BIO_new(BIO_s_mem());
-		if (PEM_write_bio_DHparams(mem, dh) == 0) {
-			qFatal("PEM_write_bio_DHparams failed: unable to write generated Diffie-Hellman parameters to memory");
-		}
-
-		char *pem = NULL;
-		long len = BIO_get_mem_data(mem, &pem);
-		if (len <= 0) {
-			qFatal("BIO_get_mem_data returned an empty or invalid buffer");
-		}
-
-		QByteArray pemdh(pem, len);
-		QSslDiffieHellmanParameters qdhp = QSslDiffieHellmanParameters::fromEncoded(pemdh);
-		if (!qdhp.isValid()) {
-			qFatal("QSslDiffieHellmanParameters: unable to import generated Diffie-HellmanParameters: %s", qdhp.errorString().toStdString().c_str());
-		}
-
-		qsdhpDHParams = qdhp;
-		setConf("sslDHParams", pemdh);
-
-		BIO_free(mem);
-		mumble_BN_GENCB_free(cb);
-		DH_free(dh);
-	}
-#endif
-
 	// Drain OpenSSL's per-thread error queue
 	// to ensure that errors from the operations
 	// we've done in here do not leak out into