SSL: upgrade the default DH parameters

We have been using as default DH parameters the 1024-bit MODP group.
This is now considered insecure, and applications should use the
2048-bit at a minimum [1]. This commit therefore replaces the parameters
with the 2048-bit MODP group from [2].

To double check the data, use openssl asn1parse to verify that the prime
matches. For instance:

1) put the encoded string in a `encoded.txt` file (c&p from the source,
   removing the double quotes)
2) put the hexadecimal value of the 2048-bit group in a `reference.txt`
   file (c&p from [2])
3) compare the output of openssl asn1parse with the reference. For
   instance like this:

    $ diff <(openssl asn1parse < encoded.txt | grep -m 1 INTEGER | perl -pe 's/.*://; s/\n//') <(perl -0777 -pe 's/\s//g' reference.txt) && echo OK
    OK

[1] https://datatracker.ietf.org/doc/html/rfc8247#section-2.4
[2] https://datatracker.ietf.org/doc/html/rfc3526#section-3

[ChangeLog][QtNetwork][QSslDiffieHellmanParameters] The default
Diffie-Hellman parameters are now using the 2048-bit MODP group from
RFC 3526.

Pick-to: 6.6 6.5 6.2 5.15
Change-Id: I47133cd78ba0e954b8f93a3da09fa2c760c9f7a8
Reviewed-by: Timur Pocheptsov <[email protected]>

2 files changed, 17 insertions, 8 deletions

diff --git a/src/network/ssl/qsslconfiguration.cpp b/src/network/ssl/qsslconfiguration.cpp
index 11d5d462214..5acadebc13a 100644
--- a/src/network/ssl/qsslconfiguration.cpp
+++ b/src/network/ssl/qsslconfiguration.cpp
@@ -919,7 +919,11 @@ void QSslConfiguration::setPreSharedKeyIdentityHint(const QByteArray &hint)
     Retrieves the current set of Diffie-Hellman parameters.
 
     If no Diffie-Hellman parameters have been set, the QSslConfiguration object
-    defaults to using the 1024-bit MODP group from RFC 2409.
+    defaults to using the 2048-bit MODP group from RFC 3526.
+
+    \note The default parameters may change in future Qt versions.
+    Please check the documentation of the \e{exact Qt version} that you
+    are using in order to know what defaults that version uses.
  */
 QSslDiffieHellmanParameters QSslConfiguration::diffieHellmanParameters() const
 {
@@ -933,7 +937,11 @@ QSslDiffieHellmanParameters QSslConfiguration::diffieHellmanParameters() const
     a server to \a dhparams.
 
     If no Diffie-Hellman parameters have been set, the QSslConfiguration object
-    defaults to using the 1024-bit MODP group from RFC 2409.
+    defaults to using the 2048-bit MODP group from RFC 3526.
+
+    \note The default parameters may change in future Qt versions.
+    Please check the documentation of the \e{exact Qt version} that you
+    are using in order to know what defaults that version uses.
  */
 void QSslConfiguration::setDiffieHellmanParameters(const QSslDiffieHellmanParameters &dhparams)
 {
diff --git a/src/network/ssl/qssldiffiehellmanparameters.cpp b/src/network/ssl/qssldiffiehellmanparameters.cpp
index b2c112bbf90..7da14f3536c 100644
--- a/src/network/ssl/qssldiffiehellmanparameters.cpp
+++ b/src/network/ssl/qssldiffiehellmanparameters.cpp
@@ -33,17 +33,18 @@
 
 QT_BEGIN_NAMESPACE
 
-// The 1024-bit MODP group from RFC 2459 (Second Oakley Group)
+// The 2048-bit MODP group from RFC 3526
 Q_AUTOTEST_EXPORT const char *qssl_dhparams_default_base64 =
-    "MIGHAoGBAP//////////yQ/aoiFowjTExmKLgNwc0SkCTgiKZ8x0Agu+pjsTmyJR"
-    "Sgh5jjQE3e+VGbPNOkMbMCsKbfJfFDdP4TVtbVHCReSFtXZiXn7G9ExC6aY37WsL"
-    "/1y29Aa37e44a/taiZ+lrp8kEXxLH+ZJKGZR7OZTgf//////////AgEC";
+    "MIIBCAKCAQEA///////////JD9qiIWjCNMTGYouA3BzRKQJOCIpnzHQCC76mOxObIlFKCHmO"
+    "NATd75UZs806QxswKwpt8l8UN0/hNW1tUcJF5IW1dmJefsb0TELppjftawv/XLb0Brft7jhr"
+    "+1qJn6WunyQRfEsf5kkoZlHs5Fs9wgB8uKFjvwWY2kg2HFXTmmkWP6j9JM9fg2VdI9yjrZYc"
+    "YvNWIIVSu57VKQdwlpZtZww1Tkq8mATxdGwIyhghfDKQXkYuNs474553LBgOhgObJ4Oi7Aei"
+    "j7XFXfBvTFLJ3ivL9pVYFxg5lUl86pVq5RXSJhiY+gUQFXKOWoqsqmj//////////wIBAg==";
 
 /*!
     Returns the default QSslDiffieHellmanParameters used by QSslSocket.
 
-    This is currently the 1024-bit MODP group from RFC 2459, also
-    known as the Second Oakley Group.
+    This is currently the 2048-bit MODP group from RFC 3526.
 */
 QSslDiffieHellmanParameters QSslDiffieHellmanParameters::defaultParameters()
 {