OPC UA vs OPC Classic
By Paul Hunkar

Security and Communication comparison
In the world of automation security has become a major source of discussion and an importantpart of most systems. The OPC Foundation has for a long time support secure interoperability
between systems made by multiple vendors, initially with its OPC DA, OPC A&E, OPC HAD and
OPC Security interfaces (collectively now termed OPC Classic) and most recently with OPC
Unified Architecture (UA). These two standards provide common functionality, but OPC UA
unifies and enhances the functionality provide by the OPC Foundation Classic interfaces. These
two standards provide, when consider from a security point of view, a somewhat different viewof security and a very different manner of implementing the view. In this paper I’ll discuss thevarious aspect of security and how they can be met by both standards and attempting tohighlight the differences.
This paper will concentrate on security as it would relate to the communication between thesystems provided by vendors. Security has many additional aspects and these should also be
considered when deploying a system, but this paper only focuses on the communication related
aspects.

This paper will try to address some of the most common aspect of Security. Security aspects
include encryption and or signing of data that is being transmitted between two systems, theidentification of applications (server and or client), the authentication and authorization of theuser of the client application, the transmission of data through firewalls and auditing. Whenconsidering security it is import to also consider the environment in which the applications are
executing.

DomainController

Multiple
Domains

Domain
DomainControllerWork Group

DomainController

Domain

DomainMix
Network
Workstation

Workstation
IphoneSmart phone
Windows
Server
VMS MainframeWorkstation

Workstation

Unix
Workstation

Android
Smart phones

Linux
Workstation

Figure 1 - Network Types

Applications could run in a Windows domain, a windows user group, on a standalone machineor in a mix operating system environment (i.e. not just windows). I’ll try to talk a little about
each of these and how they relate to OPC Classic vs OPC UA.

General Overview of OPC Classic and OPC UA Security
Let’s discuss security in general for OPC Classic. OPC Classic as a set of specifications does notdefine security as part of any of the interface specifications. OPC Classic is built on top of
DCOM/COM transport which is a Microsoft based communication protocol and has security

OPC API
Application Layer (COM/DCOM)
Session Layer RPC
Transport Layer (TCP/UDP)
Network Layer (IP)Data Link Layer (Ethernet Framing)
Physical Layer (Ethernet)

features included (see Figure 2 - OPC Classic CommunicationFigure 2). The OPC Foundation defines
recommendations for how to configure the COM/DCOM layer for security via the OPC Security
Specification. Documents have been generated that describe the Windows/DCOM provided
security and how to apply or configure it in the world of OPC Classic (see the end of the paper
for a list of related documentation). Some import configuration issues are to restrict DCOM to
TCP and to restrict access. The key aspect of DCOM / Windows security is that it is based onusers and the rights granted to the users (the user under which the application is executing). In
short OPC Classic relies on the security provided by the underlining communication protocol
and the family of Windows Operating systems. For one of the use cases, in which multiple
operating systems are present OPC Classic is very difficult to implement since it requires
COM/DCOM be available on the alternate operating system. There are some third party
versions of DCOM available for some non-windows platforms, but in general OPC Classic is very
rarely used on a non-windows platform.
OPC UA
Transport Layer (TCP)
Network Layer (IP)Data Link Layer (Ethernet Framing)
Physical Layer (Ethernet)
Figure 3 - OPC UA Communications

Let’s discuss security in general for OPC UA. OPC UA has a specification (Part 2) that describes
security threats and attacks and how the OPC UA standard is designed to mitigate these threats

and attacks. OPC UA has security related functionality included throughout the 13 part
specification. OPC UA as a standard is not locked to a single communication transport oroperating system, thus it defines security at a layer above the transport. This ensures that as
new transports are added security will be maintained. Figure 3 illustrates a TCP transport;other transports may add an additional layer between TCP and OPC UA. The security features of
OPC UA were designed to be easily enhanced as security standards improve without having to
make changes to applications. It was also modelled and made use of current best practices insecurity (think banking).
In general both OPC Classic and OPC UA have security capabilities.

Encryption and or Signing of the data flow between systems
The signing of the data flow (message) ensures that no one can change what is sent andreceived. It requires the generation of a cryptographic signature that can be easily regenerated
Signing & Encryption
AsymmetricPrivate Key

Public Certificate

or

Public Certificate

Private Key

Symmetric
Share Key

Share Key

Figure 4 - Sign and Encryptby the receiver of the message. If anything has changed the receiver will not get the same
signature and can tell the message has been altered. Encrypting takes signing to the next levelin that no one but the recipient can even read what is in the message. It uses a cryptographictranslation of what is in the message, so that only the receiver has the required information to
decrypt the message.
DCOM can be configured to provide both signing of data and encryption. In the DCOM
world this is often discussed as ensuring the data is verifiable and it is private. The setup
and configuration of it varies by version of windows and the environment in which themachine are deployed. In a Windows domain, it requires fairly simple configuration(Identifying the DCOM client(s) and server(s) and checking a box that Private
communication is required). The key point is that by default DCOM does not have thisenabled, but to secure communication it should be configured. In a non-domain

environment, it requires setup steps on each client and server machine, but this can beaccomplished as part of the required configuration for DCOM.
For OPC UA, The default transport options have Signing and Encryption enabled. The
Server configuration can choose which communication options are available to client touse for connection (i.e. the end user can select None to disable encryption and signingor can select to only allow Sign or only Sign&Encrypt). All Certified Servers and Clientsare required to support this aspect of security and it is provided by stacks and toolkits
that are used to build the application. The configuration only has to be performed onservers, client just have to choose which of the available communication option to makeuse of. Since OPC UA was architected for multiple platforms, this functionality does notchange for domain based, work groups or multiplatform based applications.

Identification and securing applications
This functionality ensures that an application is communicating only with appropriate otherapplications, that there is no man in the middle or rogue server or client. That the given client isonly communicating with an authorized server and the server is responding only to an
authorized client. This goes beyond restricting what a user does, since it restricts whichapplication instance are allow to communicate with which other application.

Figure 5 – Identifying and Securing Application

In DCOM this can be configured, but requires a fair amount of work since, since it
requires configuration of items other than DCOM, such as firewalls and RPC. Not all
OPC Classic server and clients can support this type of restriction, so testing is required.
Typically this type of restriction are not configured, instead just user access is configured(see user access).
In OPC UA, this is required and provided by default. All applications are required tosupport this to be certified. The same application installed on two different machines
can be configured with different access rights. The access rights apply to clients as well
as servers, so the same client installed on two different machines can have different
servers that it is allowed to access. For example a standard client that is installed on
two operator stations (for two different areas in a plant) would have different lists of

servers that they are allowed to connect to. This is accomplished in OPC UA by the use
of Certificates. All Applications have a unique certificate assigned to them and a trust
list that indicates which other certificates (applications) are to be trusted (allowed). The
OPC Foundation provides tools (as well as vendors) for configuring certificates andcertificate authorities (CA) allowing relatively easy configuration, especially for someone
with IT experience. OPC UA has announced Global Discover Service functionality (part12) that makes deploying certificate much easier for the non-IT person. Thisfunctionality, when it becomes available will allow management of all certificates from asingle administrative application (such as a domain) by simple menu selections.

User access rights.
This is the restriction of what items in a server can be access and in what manner they can beaccessed (read/write/browse) by a given user. For example: Is the user allowed to read values,
write values, browse the address space etc. This authorization of access implies that the user
has been identified and authenticated. The client must provide credentials to the server
identifying the user that is executing the application. User Access restrictions can be very wide
as in apply to the entire server or can be specified down to individual item in a server. User
access can also be ignored, in that it could be configured for anonymous access.

Figure 6 - User Security

DCOM typically bases its overall security on this type of server wide access. In a domain
environment it can be easily configured, but by default it is not restricted. The domain
would need to identify all OPC Classic servers and assign appropriate access rights to theUser groups (roles) associated with the clients that will be connecting. Thisconfiguration can be pushed from the domain to each Server. Since all accounts in adomain are managed from a central controller this is easy to do, but must be done toensure connectivity. In a non-domain environment it can be configured, but requires
additional work or tricks to identify and ensure users (common accounts on allmachines, common user group (roles) etc….). For the specific case of two or more

untrusted domains, user security cannot be configured, luckily this type of configured
rarely occurs. It usually only results from when two companies must share data. OPC
Classic applications may provide individual access restriction for a given item vs thegeneral DCOM read or write access, but few if any applications actually include this typeof restriction. Typically it is a wide set of access rights, in that a given user is allowed toaccess the server for read or for read/write. Other complications can a raise in thatoccasionally an application is operating under a service account (think console) and theactual operator is required to login. Typically the console application is equipped tohandle the impersonation required for these checks, but not all application will provide
this type of functionality.

Domain Controller

PKI

CRL
distribution

User
Management

Organizational role

Certificate
Template

Group

PersonCertificate
ServerPolicyApplication

Figure 7 - Domain Controller

In OPC UA, there are three options for identifying a user: A user account and password,
Kerberos tokens or certificates. All applications are required to support
Username/password, which is the simplest to implement, but can be more work to
configure, since it must be configured on each application. Kerberos is a standard
manner of exchanging user identities without exchanging passwords. It is supported bywindows domains and easily implemented in an environment that has a Kerberos token
server. Certificates are an easy extension of OPC UA, since the certificate handling isalready required for identification of applications (see 2). The selection of whichmanner of identifying user is application specific. Once the user is identified andauthenticated than the application can restrict the access rights for a given user withrespect to read/write browse etc. This is just like in DCOM where it depends on theapplication and most applications do not actually provide individual item security, they

more typically group users into groups (engineers, operator etc.) and generate
restriction by these groups server wide. OPC UA user identification works in thedomain, cross domain, multiple platform and workgroup environments in similarmanner.

Firewalls
Firewalls are used in systems to protect machines and access points from intrusion. They
function by restricting the types of connection that are allowed, the ports to which connection
are allowed and the communication protocols allowed. They are becoming mandatory in most
systems to ensure security.

Figure 8 - Firewalls

OPC Classic makes use of DCOM, which intern makes use of RPC. RPC by default makes
use of dynamic port allocation. This makes it very difficult to configure a firewall, since alarge range of ports would need to be opened. In addition in OPC Classic, the serverneeds to be able to initiate communication with a client for callbacks requiring accessfrom a server to a client. This functionality results in requiring all client machines to also
be configured as if they were server and all server machines to also be configured as if
they were a client, i.e. Opening the firewall in the opposite direction. RPC can be
configured to either restrict the range of ports that are used or can statically assign afixed port to a given OPC Classic server. The fixed port assignment may not work for all
OPC Classic products so a given vendors offering should be tested to ensure it will allow
the static port. DCOM is a standard protocol
OPC UA defines a fixed port or ports for a communication channel. The actual port isdetermined by the endpoint(s) and protocol(s) exposed by the server. The HTTP
protocol can run over the default port 80, which is rarely blocked. Clients initiate allcommunication so no out bound communication. The fixed ports and client initiatedcommunication result in very easy firewall configuration. The OPC Foundation
configuration tool will (depending on the firewall being used) perform this configuration
at the touch of a button.

Auditing
Auditing is the generation of messages that track all security related actions in a system. It
includes all failed attempts to connect to the system, who successfully connects to a system,
any actions they perform that alter the system, any errors or security violation that occur. The
purpose of audit records is to allow an analysis of the actions in a system after some problem is
detected. It can also be analyzed to detect problems.
DCOM/COM does not by default generate any level of logs, but users can enable logging
for DCOM Connection requests, System Object Access and SMB logins. By enablingthese, the operating system can generate events that can be used to track activity. This
still does not provide detailed information as to what the activity was, only the “whoconnected”. What was written to would require additional auditing functionality is built
into the classic application. This type of auditing is not defined as part of any OPC
Classic specification.
OPC UA defines audit messages and when they are required. An OPC UA server that
supports the Auditing profile can generate audit events for all connection and security
related actions. In addition it generates audit events for all user actions that makechanges to the address space on the server. The auditing provided by OPC UA also
supports linking of audit events from the client to the server allowing easier review ofaudit logs from multiple devices.

Conclusions
OPC Classic can be configured to provide a fair amount of security, but all of the security Is
actually provided by the functionality in Windows and DCOM/COM. It does require a fairamount of configuration and knowledge to configure. Some environments do not support
security configuration and some application cannot be configured to support all security
configuration.
OPC UA was designed with security in mind and thus has security integrated throughout the setof specifications. To become certified an application must support all basic security
functionality. OPC UA is designed to work in multiple environments and on multiple platforms,
but as a result it is not tied to one platform and the security built into the platform.

Author
PAUL HUNKAR is president of DS Interoperability, independent consulting firm, specializing in design anddevelopment of software systems. He has been running DS Interoperability for 4 years, his client list includes
Yokogawa, ABB, Unified Automation, RoviSys, the OPC Foundation. Paul is member of the Technical Advisory
Council of the OPC Foundation. He is editor for the Profiles, Security, and Alarm & Condition parts of the OPC UA
Specification. He was the Director of Certification for the OPC Foundation and the chair of the OPC Foundation
Compliance Working Group. He is Chair of the ISA-95 OPC UA working group. He had previously worked for major
Process Automation vendors for more than 25 years in a variety of engineering roles including designing,
constructing and managing development of advanced control applications, operator interface systems, historicalsystems and investigating new technologies. Paul has a Bachelors Degree in Computer Engineering from the
University of Michigan and a Masters Degree in Computer Engineering from Case Western Reserve University.
DSInteroperability,
Hudson, Ohio,
Tel. +1 440 337 4161,
E-Mail: Paul.Hunkar@DSInteroperability.com

References
The following documents can be used to further investigate OPC security.
OPC Security 1.00 Specification
Unified Architecture security
Securing your OPC classic control system
Using OPC via DCOM with windows XP service pack 2
OPC, DCOM and Security
The OPC UA Security Model for Administrator
OPC Security White Paper #1
OPC Security White Paper #2
OPC Security White Paper #3
OPC UA 1.02 Part 2: Security Model
OPC UA 1.02 Part 4: Services
OPC UA 1.02 Part 6: Mappings
OPC UA 1.02 Part 12: Discover