A Secure DCE and Kerberos Server

DICCE Proposal

April 28, 1996


ESNet has decided to use The distributed Computing Environment (DCE) and Kerberos Version 5 to provide inter-realm authentication as well as secure file access. However, this system is only as secure as the servers that provide keys, tickets, and initial user login verification. Compartmented Mode Workstations (CMW) are rated B1 secure by the National Computer Security Center (NCSC) and in fact have many security features from higher levels of assurance. The funds from this proposal would be used to install and test DCE and Kerberos 5 servers on distributed CMW system.

Principal Investigators

James A. Rome
Networking Group
Computer Science and Mathematics Division
Building 6012, MS 6367
Oak Ridge National Lab
P. O. Box 2008
Oak Ridge, TN 37831-63671
(423) 574-1306 FAX: (423) 574-0680

Douglas E. Engert
Systems Programming
Argonne National Laboratory
9700 South Cass Avenue Argonne, IL 60439
(708) 252-5444


A recent report by Attorney General Reno identified cyber-terrorism as an even greater concern than incidents such as the Oklahoma City bombing. This has lead to the formation of a White House panel to study the problem. Senator Nunn is now holding hearings on the whole area of information warfare. In this environment, distributed computing cannot become a reality without a high level of security that is applied to all portions of the distributed computing environment. This realm can be divided into three venues than have their own security needs and solutions.

The Wide-Area Network (WAN):

The security of traffic between computer sites, as well as authentication and access to remote resources have been the main focus of the DICCE initiative. The DICCE solution to this problem has been the implementation of the Open Software Foundation's DCE plus MIT's Kerberos Version 5. Although this solution is complicated and expensive, it is presently the only solution that is available across a wide spectrum of computing platforms.

The Wide Area Network - Local Area Network (LAN) Interface:

The Internet connection(s) can be secured by means of a properly programmed router, or by a firewall. Complicated router programs reduce throughput. Firewalls can look inside the packets to make intelligent decisions that can depend upon the actual application being used, but this takes a powerful firewall machine and reduces throughput even further.

The Individual Computing Node:

Unix workstations have a built-in level of security that was designed for an era before attacks on computer systems were common. Nonetheless, file permissions, hidden password files, and controls upon the reuse of system resources do provide some resistance to attacks.

However, the complicated nature of the operating system and their historical baggage imply that there are numerous bugs that can be exploited by attackers. CIAC works with computer manufacturers to provide fixes for most (but not all) of these attack vectors, but being sure that these patches are applied to all machines on a computer network is an administrator's nightmare. Because a system is only as strong as it's weakest host, machines with security holes can be compromised. Attacks that are carried out from a compromised machine that is inside the local network bypass many of the controls that have already been discussed, and thus are more likely to succeed.

Host machines that are required to perform important security functions should be more resistant to attack than ordinary nodes. Servers for DCE and Kerberos 5 certainly fall into this category. Fortunately, the CMW operating system provides this higher level of assurance. CMW was designed for use by the military to handle multilevel classified data in a manner that would ensure its protection and integrity. The latest generation of CMW systems work well enough that they can now should be exploited for nonmilitary purposes.

CMW achieves its security goals by enforcing Mandatory Access Controls (MAC) which label all files on the system with a security level and compartment(s). In addition the role of the superuser is broken up into about 50 different privileges. All of the usual Unix utility programs (ls, chmod, mount,....) have been rewritten to only assume a privilege when it is needed, and to drop it when it is no longer needed. This is called the Principle of Least Privilege. In addition, by default, users do not have the authorization to run commands such as chown or mount that could be used to provide unauthorized access to data. This effort succeeds. For example, Sun Microsystems claims that none of the CERT/CIAC computer advisories has ever applied to their CMW systems.

Proposed Research

Currently, DCE or Kerberos is not supported by any CMW operating system. The reason for this is that these systems assume that they are on a secure network. Also, there is a question of what DCE would mean in a multilevel-secure environment. We believe that we can successfully install DCE and Kerberos servers for non-CMW systems on a CMW host. We have discussed this issue with Hewlett-Packard (HP), the manufacturer of the CMW platform we propose to use, and a major player in the DCE initiative. HP feels that it should be possible to achieve this goal by using the DCE that they developed for standard HP-UX. However, HP has not tried DCE in a CMW environment, so there is some possibility that the effort will fail.

One issue that must be resolved is host access to the CMW system. One way CMW systems resist attack is by only communicating with hosts whose ip addresses and security features (multilevel, unlabeled,...) are listed in the secure file M6RHDB. A CMW machine will not even answer a ping from an ip address that is not listed in this file.

In a cross-realm environment, it is the foreign client that contacts the security server presenting a ticket, and asking for another ticket. The two security servers do not communicate directly, they only share a key. They communicate via the client, giving and receiving tickets which are encrypted in the shared key. On a local cell, it might be possible to list all of the clients in the M6RHDB file, but this would be almost impossible to do with foreign clients. A similar situation applies with portable computers which change their ip address according to their location. Thus, we will have to develop a method for allowing non-listed hosts to communicate with the CMW server.

In the first phase of this proposal, we plan to install two CME DCE servers, one at ANL and the other at ORNL. Two servers are required because CMW workstations can only be administered from the console.

In addition to providing resistance to attack, the CMW concept can be used in its own right. The CMW's security labels can be employed to control access to resources by both their sensitivity, and their "need to know." For example, all researcher's on a project should be able to access the project's data files, but perhaps only the leaders should be able to access the financial data. In phase two of this project, we propose to implement these access controls by setting up a DFS server on the CMW host. Access to these files will have to pass the additional MAC authentication of the CMW system. This scheme can provide protection for proprietary data that is much higher than on a conventional Unix system. Given the increasing exposure of government agencies to lawsuits in this area, we believe that these added precautions might prove to be necessary in the near future. CMW hosts might also be an ideal platform for certification authority and public key servers.


PDF file of a talk given by James Rome at the September, 1995 DICCE Meeting:


Oak Ridge National Laboratory has a network of six CMW workstations that we administer and use as a development platform. In particular, James Rome is the technical lead in the DOE-OSS file room project which is using modified COTS packages to create a multilevel-secure file room on a CMW host. ORNL has installed Kerberos on several systems in Y-12, and is about to set up a DCE test cell.

Argonne National Laboratory has been operating two DCE test cells, and has been using Kerberos Version 4 and Version 5 for a number of years. Douglas Engert is the Chairman of the ESnet Authentication Task Force, and has been very active in the Kerberos/DCE interoperability activities and in cross-realm authentication testing and design.


Start Date:

Funds awarded

Start Date + 6 months:

DCE, hardware, and Kerberos 5 procured and installed with a local cell.

Start Date + 9 months:

System integrated into DICCE cross-realm authentication effort.

Start Date + 15 months:

Multilevel DFS server set up and operational.


The project will produce both technical reports and journal articles that describe the steps necessary to get DCE + Kerberos servers to work on a CMW host. A System Administrator's Manual will be produced that will allow other sites to implement these servers with minimal amounts of grief.


$36k Capital equipment to procure two HP C-100 CMW servers (one at ANL and one at ORNL), CMW software and support. It takes about three months to procure these items.

$15k OSF/DCE server software (2 copies).

$130k = 1/2 FTE for 1 1/4 years ,split between ANL and ORNL.

($20k in FY '96, $110k in FY '97)