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Connection failure with Milo Server and 4096 bit private key

Posted: 18 May 2020, 11:56
by WoDann

I´m testing a client which is created with the .NET UA Client SDK V2.6.4.
The OPC UA Server is programmed with Java Milo SDK from external.

The connection establishment to the server with 2048 bit private key is working fine. Here the settings:

Endpoint Settings: Basic256Sha256, Sign&Encrypt, Anonymous,
Server & Client Certificate Settings: 2048 bit, sha256

When I change to 4096 bit private key with according server and client certificates, the connection establishment end withs the error ("BadInvalidArgument" was returned during OpenSecureChannel).

When I using the public demo server from Milo ( at the bottom of the page) then I have the same error behaviour with the 4096bit key. With the 2048 bit I can connect to the Server.
The same error behavior is present when I using the UaExpert V1.5.1 to connect to the server.

Did anyone else have a similar error behaviour or can support a bug fix?
How can I connect with a 4096bit private key to the Milo Server?


Re: Connection failure with Milo Server and 4096 bit private key

Posted: 19 May 2020, 19:21
by Support Team

have you ever tried with a different server to narrow down the problem?

There are different free DemoServers on our Website for free download which you can use to test. One of the big advantages of our professional offerings is, that such DemoServer were tested and certified for compliance with the OPC Specification by the official test laboratory. Therefore it is some what unlikely that such basic features do not work properly.

I assume the Milo Server has no compliance tested certificate, hence the error is probably in the Milo.

Please understand that we do not give any support for any implementation other than Unified Automation originals.

Re: Connection failure with Milo Server and 4096 bit private key

Posted: 25 May 2020, 15:51
by WoDann

Thank your for the quick response.

Yes, I connected the client to the UaServerNet example with 4096 bit certificate and it works fine.
I found the following issue on github for the Milo SDK:
(It´s only 22days ago)

The error message describes a very similar error behavior as it is with me.
After the update to the newest release is done I will test the Milo Server again.