src/java.base/share/classes/sun/security/ssl/ServerHandshaker.java

8072452 Support DHE sizes up to 8192-bits

@@ -136,15 +136,21 @@
         } else {
             useLegacyEphemeralDHKeys = false;
             useSmartEphemeralDHKeys = false;
 
             try {
+                // Note: the current supported pre-computed groups are of
+                // 512, 768, 1024, 1536, 2048, 3072, 4096, 6144, 8192 bits.
+                //
+                // Except for the customized groups, please DON'T use value
+                // other than the pre-computed sizes as DH parameter
+                // generation can be extremely slow.
                 customizedDHKeySize = Integer.parseUnsignedInt(property);
-                if (customizedDHKeySize < 1024 || customizedDHKeySize > 2048) {
+                if (customizedDHKeySize < 1024) {
                     throw new IllegalArgumentException(
-                        "Customized DH key size should be positive integer " +
-                        "between 1024 and 2048 bits, inclusive");
+                        "Customized DH key size should larger " +
+                        "than 1024 bits");
                 }
             } catch (NumberFormatException nfe) {
                 throw new IllegalArgumentException(
                         "Invalid system property jdk.tls.ephemeralDHKeySize");
             }

@@ -1518,19 +1524,15 @@
          * keys and key-exchange keys.
          *
          * Applications may also want to customize the ephemeral DH key size
          * to a fixed length for non-exportable cipher suites. This can be
          * approached by setting system property "jdk.tls.ephemeralDHKeySize"
-         * to a valid positive integer between 1024 and 2048 bits, inclusive.
+         * to a valid positive integer larger than 1024 bits.
          *
          * Note that the minimum acceptable key size is 1024 bits except
          * exportable cipher suites or legacy mode.
          *
-         * Note that the maximum acceptable key size is 2048 bits because
-         * DH keys bigger than 2048 are not always supported by underlying
-         * JCE providers.
-         *
          * Note that per RFC 2246, the key size limit of DH is 512 bits for
          * exportable cipher suites.  Because of the weakness, exportable
          * cipher suites are deprecated since TLS v1.1 and they are not
          * enabled by default in Oracle provider. The legacy behavior is
          * reserved and 512 bits DH key is always used for exportable

@@ -1541,15 +1543,17 @@
             if (useLegacyEphemeralDHKeys) {          // legacy mode
                 keySize = 768;
             } else if (useSmartEphemeralDHKeys) {    // matched mode
                 if (key != null) {
                     int ks = KeyUtil.getKeySize(key);
-                    // Note that SunJCE provider only supports 2048 bits DH
-                    // keys bigger than 1024.  Please DON'T use value other
-                    // than 1024 and 2048 at present.  We may improve the
-                    // underlying providers and key size here in the future.
+                    // Note: the current supported pre-computed groups are of
+                    // 512, 768, 1024, 1536, 2048, 3072, 4096, 6144, 8192 bits.
                     //
+                    // Except for the customized groups, please DON'T use value
+                    // other than the pre-computed sizes as DH parameter
+                    // generation can be extremely slow.
+                    //
                     // keySize = ks <= 1024 ? 1024 : (ks >= 2048 ? 2048 : ks);
                     keySize = ks <= 1024 ? 1024 : 2048;
                 } // Otherwise, anonymous cipher suites, 1024-bit is used.
             } else if (customizedDHKeySize > 0) {    // customized mode
                 keySize = customizedDHKeySize;