| This article about computer security describes how security can be achieved through design and engineering. Please see
computer insecurity article for an alternative approach that
describes the current battlefield of computer security exploits and defenses.
Computer security is the effort to create a secure computing platform, designed so that agents (users or
programs) can only perform actions that have been
allowed. This involves specifying and implementing a security policy.
The actions in question can be reduced to operations of access, modification and deletion. Computer security can be seen as a
subfield of security engineering, which looks at broader
security issues in addition to computer security.
It is important to understand that in a secure system, the legitimate users of that system are still able to do what they
should be able to do. It has been said pejoratively that the only truly secure computer is one locked in a vault without any
means of power or communication; however, this would not be regarded as a useful secure system because of the above
requirement.
It is also important to distinguish the techniques employed to increase a system's security from the issue of that system's
security status. In particular, systems which contain fundamental flaws in their security designs cannot be made secure without
compromising their utility. Consequently, most computer systems cannot be made secure even after the application of extensive
"computer security" measures.
Computer security by design
There are two different approaches to security in computing. One focuses mainly on external threats, and generally
treats the computer system itself as a trusted system. This philosophy is discussed in the computer insecurity article.
The other, discussed in this article, regards the computer system itself as largely an untrusted system, and redesigns it to
make it more secure in a number of ways.
This technique enforces privilege separation, where an
entity has only the privileges that are needed for its function. That way, even if an attacker has subverted one part of the system, fine-grained security ensures that it is just as difficult for them
to subvert the rest.
Furthermore, by breaking the system up into smaller components, the complexity of individual components is reduced, opening up
the possibility of using techniques such as automated
theorem proving to prove the correctness of crucial software subsystems. Where formal correctness proofs are not possible,
rigorous use of code review and unit testing measures can be used to try to make modules as secure as possible.
The design should use "defense in depth", where more than one
subsystem needs to be compromised to compromise the security of the system and the information it holds. Subsystems should
default to secure settings, and wherever possible should be designed to "fail secure" rather than "fail insecure" (see fail safe for the equivalent in safety engineering). Ideally, a secure system should
require a deliberate, conscious, knowledgeable and free decision on the part of legitimate authorities in order to make it
insecure.
In addition, security should not be an all-or-nothing issue. The designers and operators of systems should assume that
security breaches are inevitable in the long term. Full audit trails should
be kept of system activity, so that when a security breach occurs, the mechanism and extent of the breach can be determined.
Storing audit trails remotely, where they can only be appended to, can keep intruders from covering their tracks. Finally,
full disclosure helps to ensure that when bugs are found the
"window of
vulnerability" is kept as short as possible.
Early history of security by design
The early Multics operating system was notable for its early emphasis on computer
security by design, and Multics was possibly the very first operating system to be designed as a secure system from the ground
up. In spite of this, Multics security was broken, not once, but repeatedly. This led to further work on computer security that
prefigured modern security engineering techniques..
Techniques for creating secure systems
The following techniques can be used in engineering secure systems. Note that these techniques, whilst useful, do not of
themselves ensure security -- a security system is no stronger than its weakest link.
- Automated theorem proving and other
verification tools can enable critical algorithms and code used in secure systems to be mathematically proven to meet their
specifications.
- Thus simple microkernels can be written so that we can be
sure they don't contain any bugs: eg EROS[1] (http://www.eros-os.org/) and Coyotos[2] (http://coyotos.org/).
- A bigger OS, able of providing a standard API like POSIX, can be built on a microkernel using small API servers running as
normal programs. If one of these API servers has a bug, the kernel and the other servers are not affected: eg Hurd.
- Cryptographic techniques can be used to defend data in transit between
systems, reducing the probability that data exchanged between systems can be intercepted or modified.
- Strong authentication techniques can be used to ensure that
communication end-points are who they say they are.
- Secure cryptoprocessors can be used to leverage
physical security techniques into protecting the security of the
computer system.
- Chain of trust techniques
can be used to attempt to ensure that all software loaded has been certified as authentic by the system's designers.
- Mandatory access control can be used to ensure
that privileged access is withdrawn when privileges are revoked. For example, deleting a user account should also stop any
processes that are running with that user's privileges.
- Capability and access control list techniques can be used to ensure privilege
separation and mandatory access control. The next sections discuss their use.
Some of the following items may belong to the computer
insecurity article:
- In a production system when an application provides no
way to patch already known security flaws, don't use it or use another one (at least until the fix is available). Publicly known
flaws are the main entry used by worms to automatically break into a
system and then spread to other systems connected to it. The security website Secunia
provides a search tool for unpatched known flaws in popular products.
-
- Backups are a way of securing your information; they are another copy of all your
important computer files kept in another location. These files are kept on hard disks, CD-R’s, CD-RW’s, and tapes.
Backups can be kept in a multitude of locations, some of the suggested places would be a fireproof, waterproof, and heat proof
safe, or separate location than that in which the original files are contained. There is also a third option, which involves
using one of the companies on the internet that backs up files for both business and individuals.
- Anti-virus software deletes or quarantines viruses on your computer, in essence protecting you against viruses. This
software once on your computer needs to be updated regularly, as there are new viruses created daily. There are a couple things
that are an important part of any antivirus software, one should look for a good detection rate, compatibility with your system,
easy to use, and must have the ability to update.
- Firewalls are hardware and/or software components that protects computers from
intruders. The firewall will not allow anything to enter your computer without the correct markings. All networks require a
firewall to keep out people and files that are hazardous to the system.
- Access authorization is a way of protecting your computer by using
authentication systems, so you know who is trying to get in. This
system would allow only those with authorized access into certain areas of the computer or to open certain files. There are a lot
of methods in detecting one's identity. The most commonly used are passwords or
identification cards, however as technology advances more
methods are becoming common such as smart cards or biometrics, for example with fingerprints.
- Encryption is used to protect your message from the eyes of others. It can
be done in several ways by switching the characters around, replacing characters with others, and even removing characters from
the message. These have to be used in combination to make the encryption secure enough, that's to say difficult to crack. Public
key encryption is a refined and practical way of doing encryption. It allows for example anyone to write a message for a list
of recipients, and only those recipients will be able to read that message.
- Intrusion-detection systems can scan a
network for people that are on the network but who should not be there or are doing things that they should not be doing, for
example trying a lot of passwords to gain access to the network.
Capabilities vs. ACLs
Within computer systems, the two fundamental means of enforcing privilege separation are access control lists (ACLs) and capabilities. The semantics of ACLs have been proven to be insecure in many situations (e.g.,
Confused deputy problem). It has also been shown that
ACL's promise of giving access to an object to only one person can never be guaranteed in practice. Both of these problems are
resolved by capabilities. This does not mean practical flaws exist in all ACL-based systems — only that the designers of
certain utilities must take responsibility to ensure that they do not introduce flaws.
Unfortunately, for various historical reasons, capabilities have been mostly restricted to research operating systems and commercial OSes still use ACLs. Capabilities can,
however, also be implemented at the language level, leading to a style of programing that is essentially a refinement of standard
object-oriented design. An open source project in the area is the E language[3] (http://www.erights.org/).
The Cambridge CAP computer demonstrated the use of capabilities, both in
hardware and software, in the 1970s, so this technology is hardly new. A reason for the
lack of adoption of capabilities may be that ACLs appeared to offer a 'quick fix' for security without pervasive redesign of the
operating system and hardware.
A good example of a current secure system is Eros. But see also the article on secure operating systems. TrustedBSD is an
example of an opensource project with a goal, among other things, of building
capability functionality into the FreeBSD operating system. Much of the work is
already done.
Other uses and misuses of the term "trusted"
The term "trusted" is often applied to operating systems that meet different levels of the common criteria, some of which are discussed above as the techniques for creating secure systems.
Unfortunately for users, a computer industry group led by Microsoft, in an
attempt to market a different set of products and services, has taken the term "trusted system" and changed it to include making
computer hardware that prevents the user from having full control over their own system. They call their project the Trusted Computing Platform Alliance
(TCPA). See also Next-Generation Secure Computing Base.
Further reading
Computer security is a highly complex field, and it is relatively immature. The ever-greater amounts of money dependent on
electronic information make protecting it a growing industry and an active research topic.
Notable persons in computer security
For additional persons, see also: Category:Cryptographers.
References
- Ross J. Anderson: Security Engineering: A Guide to Building
Dependable Distributed Systems, ISBN
0471389226
- Bruce Schneier: Secrets & Lies: Digital Security in a
Networked World, ISBN
0471253111
- Paul A. Karger, Roger R. Schell: Thirty Years
Later: Lessons from the Multics Security Evaluation, IBM white paper.
- Clifford Stoll: Cuckoo's Egg: Tracking a Spy Through the Maze
of Computer Espionage, Pocket Books, ISBN 0743411463
- Stephen Haag, Maeve Cummings, Donald McCubbrey, Alain Pinsonneault, Richard Donovan: Management
Information Systems for the information age, ISBN 0070911207
External links
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