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OPC Unified Architecture (OPC UA) is a protocol for industrial automation. This protocol, which is managed by OPC Foundation, is a successor of the successful and often used OPC (OPC DA or OPC Classic) protocol. Unlike its predecessor, it is not based on  Windows technologies (OLE, COM), thus available also on other platforms (e.g. PLC Simatic, or Bernecker & Rainer).

D2000 OPC UA Server allows OPC UA third-party clients to access the objects of the D2000 system - to read them and to write their values.

D2000 OPC UA Server is located in the installation directory of D2000 installation under the name "opcuaserver.exe" (i.e. "opcuaserver" on Linux and Raspbian).

Characteristics of D2000 OPC UA Server

Support of opc.tcp:// protocol.

Support for multiple OPC UA clients connected in parallel (multiserver).

Support of identities:

  • name:password

Support of security policies:

  • None
  • Basic128Rsa15
  • Basic256
  • Basic256Sha256

Message Security Modes:

  • None
  • Sign
  • Sign&Encrypt

Configuration of a user for D2000 OPC UA Server

For D2000 OPC UA Server to access the individual objects of the D2000 system, it is necessary to create a user in the D2000 system under which the OPC UA Server logs in to D2000 Server. OPC UA Server receives access rights of this user. User name must be in "OPCUA_User_<process_name_opcua>" format. For instance, if OPC UA Server is named "SELF.OUS" (default, the process name can be changed with /W switch), then the name of the relevant user will be "OPCUA_User_SELF". It is necessary to set this user's access rights to objects of the D2000 system. These access rights will be monitored while reading/writing values by the OPC client. 

Configuration of D2000 OPC UA Server

OPC UA Server configuration is read from a file. It is vital to specify the path to a configuration file by the starting parameter --cfg=<path_to_configuration_file>, for example "opcuaserver.exe --cfg=c:\D2000\D2000_APP\application1\opcuaserver\opcuaserver.conf". Sample configuration file is located in the program directory in a subdirectory Templates\opcuaserver\ (resp. .sys\templates\opcuaserver\ on Linux). In this file, some parameters are already preset. It is necessary to set at least the pki_dir parameter and create a directory structure for PKI.

It is possible to specify the following parameters in the configuration file:

application_namename of the application
application_uriURI applications
pki_dirfull path to PKI directory structure (e.g. 'c:\D2000\D2000_APP\application1\opcuaserver\pki')
tcp_config.hostthe address of network adapter on which OPC UA Server accepts connections ( for all network adapters)
tcp_config.portthe port on which OPC UA Server accepts connections
user_tokensthe list of configured users under which OPC UA clients can log in
endpointsthe list of access points of the OPC UA Server

The configuration file is read during the OPC UA Server startup, so the adjustments of parameters in the file will show only after a restart. If PKI directory structure does not exist, OPC UA Server creates it (empty, without keys and certificates), based on the settings of pki_dir parameter.

Configuration of PKI (public key infrastructure)

For running a secure communication between OPC UA Server and OPC UA client, it is necessary for OPC UA Server to create PKI directory structure, private key, and a certificate.

Directory structure consists of directories:

directory namedescription
pki/PKI directory
pki/private/directory with a private key of OPC UA Server
pki/own/directory with a public certificate of OPC UA Server
pki/rejected/directory with a certificate of denied clients
pki/trusted/directory with a certificate of allowed clients

It is essential to secure the private key against unauthorized access.

Private key generation and certificate signing request using openssl utility :

openssl req -out csr.csr -new -newkey rsa:2048 -nodes -keyout pki/private/private.pem

Creation of self-signed certificate:

openssl x509 -req -days 365 -in csr.csr -signkey pki/private/private.pem -outform der -out pki/own/cert.der

Management of OPC UA Clients certificates

OPC UA Server sends its certificate to the OPC UA client during the establishment of a secured connection. When an unknown OPC UA client connects, OPC UA Server rejects the client and saves their certificate into "pki/rejected/" directory. After that, the administrator of the D2000 application has to manually move that certificate into "pki/trusted/" directory. This ensures that the server will consider the given client trustworthy and will accept the connection. 

Management of OPC UA Clients names and passwords

Configuration of OPC UA clients' names and passwords is in the opcuaserver.conf configuration file. Only a single user token sample_user with user name sample and password sample1 is predefined:

     user: sample
     pass: sample1

User tokens, as well as anonymous access (ANONYMOUS) permitted for individual endpoints, are defined in the definition of respective endpoints:

     path: /
     security_policy: Basic256Sha256
     security_mode: SignAndEncrypt
     security_level: 4
       - ANONYMOUS
       - sample_user

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