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Those who take computer security very seriously indeed point out that, when your Mac enters sleep mode (if you close the lid of a MacBook Pro, for example), there's a potential security hole in.

Multilevel security or multiple levels of security (MLS) is the application of a computer system to process information with incompatible classifications (i.e., at different security levels), permit access by users with different security clearances and needs-to-know, and prevent users from obtaining access to information for which they lack authorization. There are two contexts for the use of multilevel security. One is to refer to a system that is adequate to protect itself from subversion and has robust mechanisms to separate information domains, that is, trustworthy. Another context is to refer to an application of a computer that will require the computer to be strong enough to protect itself from subversion and possess adequate mechanisms to separate information domains, that is, a system we must trust. This distinction is important because systems that need to be trusted are not necessarily trustworthy.

Trusted operating systems[edit]

An MLS operating environment often requires a highly trustworthy information processing system often built on an MLS operating system (OS), but not necessarily. Most MLS functionality can be supported by a system composed entirely from untrusted computers, although it requires multiple independent computers linked by hardware security-compliant channels (see section B.6.2 of the Trusted Network Interpretation, NCSC-TG-005). An example of hardware enforced MLS is asymmetric isolation.^[1] If one computer is being used in MLS mode, then that computer must use a trusted operating system (OS). Because all information in an MLS environment is physically accessible by the OS, strong logical controls must exist to ensure that access to information is strictly controlled. Typically this involves mandatory access control that uses security labels, like the Bell–LaPadula model.

Customers that deploy trusted operating systems typically require that the product complete a formal computer security evaluation. The evaluation is stricter for a broader security range, which are the lowest and highest classification levels the system can process. The Trusted Computer System Evaluation Criteria (TCSEC) was the first evaluation criteria developed to assess MLS in computer systems. Under that criteria there was a clear uniform mapping^[2] between the security requirements and the breadth of the MLS security range. Historically few implementations have been certified capable of MLS processing with a security range of Unclassified through Top Secret. Among them were Honeywell's SCOMP, USAF SACDIN, NSA's Blacker, and Boeing's MLS LAN, all under TCSEC, 1980s vintage and Intel 80386-based. Currently, MLS products are evaluated under the Common Criteria. In late 2008, the first operating system (more below) was certified to a high evaluated assurance level: Evaluation Assurance Level (EAL) - EAL 6+ / High Robustness, under the auspices of a U.S. government program requiring multilevel security in a high threat environment. While this assurance level has many similarities to that of the old Orange Book A1 (such as formal methods), the functional requirements focus on fundamental isolation and information flow policies rather than higher level policies such as Bell-La Padula. Because the Common Criteria decoupled TCSEC's pairing of assurance (EAL) and functionality (Protection Profile), the clear uniform mapping between security requirements and MLS security range capability documented in CSC-STD-004-85 has largely been lost when the Common Criteria superseded the Rainbow Series.

Freely available operating systems with some features that support MLS include Linux with the Security-Enhanced Linux feature enabled and FreeBSD.^[3] Security evaluation was once thought to be a problem for these free MLS implementations for three reasons:

1. It is always very difficult to implement kernel self-protection strategy with the precision needed for MLS trust, and these examples were not designed to or certified to an MLS protection profile so they may not offer the self-protection needed to support MLS.
2. Aside from EAL levels, the Common Criteria lacks an inventory of appropriate high assurance protection profiles that specify the robustness needed to operate in MLS mode.
3. Even if (1) and (2) were met, the evaluation process is very costly and imposes special restrictions on configuration control of the evaluated software.

Notwithstanding such suppositions, Red Hat Enterprise Linux 5 was certified against LSPP, RBACPP, and CAPP at EAL4+ in June 2007.^[4] It uses Security-Enhanced Linux to implement MLS and was the first Common Criteria certification to enforce TOE security properties with Security-Enhanced Linux.

Vendor certification strategies can be misleading to laypersons. A common strategy exploits the layperson's overemphasis of EAL level with over-certification, such as certifying an EAL 3 protection profile (like CAPP)^[5] to elevated levels, like EAL 4 or EAL 5. Another is adding and certifying MLS support features (such as role-based access control protection profile (RBACPP) and labeled security protection profile (LSPP)) to a kernel that is not evaluated to an MLS-capable protection profile. Those types of features are services run on the kernel and depend on the kernel to protect them from corruption and subversion. If the kernel is not evaluated to an MLS-capable protection profile, MLS features cannot be trusted regardless of how impressive the demonstration looks. It is particularly noteworthy that CAPP is specifically not an MLS-capable profile as it specifically excludes self-protection capabilities critical for MLS.

General Dynamics offers PitBull, a trusted, MLS operating system. PitBull is currently offered only as an enhanced version of Red Hat Enterprise Linux, but earlier versions existed for Sun Microsystems Solaris, IBM AIX, and SVR4 Unix. PitBull provides a Bell LaPadula security mechanism, a Biba integrity mechanism, a privilege replacement for superuser, and many other features.PitBull has the security base for General Dynamics' Trusted Network Environment (TNE) product since 2009. TNE enables Multilevel information sharing and access for users in the Department of Defense and Intelligence communities operating a varying classification levels. It's also the foundation for the Multilevel coalition sharing environment, the Battlefield Information Collection and Exploitation Systems Extended^[6] (BICES-X).

Sun Microsystems, now Oracle Corporation, offers Solaris Trusted Extensions as an integrated feature of the commercial OSs Solaris and OpenSolaris. In addition to the controlled access protection profile (CAPP), and role-based access control (RBAC) protection profiles, Trusted Extensions have also been certified at EAL4 to the labeled security protection profile (LSPP).^[7] The security target includes both desktop and network functionality. LSPP mandates that users are not authorized to override the labeling policies enforced by the kernel and X Window System (X11 server). The evaluation does not include a covert channel analysis. Because these certifications depend on CAPP, no Common Criteria certifications suggest this product is trustworthy for MLS.

BAE Systems offers XTS-400, a commercial system that supports MLS at what the vendor claims is 'high assurance'. Predecessor products (including the XTS-300) were evaluated at the TCSEC B3 level, which is MLS-capable. The XTS-400 has been evaluated under the Common Criteria at EAL5+ against the CAPP and LSPP protection profiles. CAPP and LSPP are both EAL3 protection profiles that are not inherently MLS-capable, but the security target^[8] for the Common Criteria evaluation of this product contains an enriched set of security functions that provide MLS capability.

Problem areas[edit]

Sanitization is a problem area for MLS systems. Systems that implement MLS restrictions, like those defined by Bell–LaPadula model, only allow sharing when it does not obviously violate security restrictions. Users with lower clearances can easily share their work with users holding higher clearances, but not vice versa. There is no efficient, reliable mechanism by which a Top Secret user can edit a Top Secret file, remove all Top Secret information, and then deliver it to users with Secret or lower clearances. In practice, MLS systems circumvent this problem via privileged functions that allow a trustworthy user to bypass the MLS mechanism and change a file's security classification. However, the technique is not reliable.

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Covert channels pose another problem for MLS systems. For an MLS system to keep secrets perfectly, there must be no possible way for a Top Secret process to transmit signals of any kind to a Secret or lower process. This includes side effects such as changes in available memory or disk space, or changes in process timing. When a process exploits such a side effect to transmit data, it is exploiting a covert channel. It is extremely difficult to close all covert channels in a practical computing system, and it may be impossible in practice. The process of identifying all covert channels is a challenging one by itself. Most commercially available MLS systems do not attempt to close all covert channels, even though this makes it impractical to use them in high security applications.

Bypass is problematic when introduced as a means to treat a system high object as if it were MLS trusted. A common example is to extract data from a secret system high object to be sent to an unclassified destination, citing some property of the data as trusted evidence that it is 'really' unclassified (e.g. 'strict' format). A system high system cannot be trusted to preserve any trusted evidence, and the result is that an overt data path is opened with no logical way to securely mediate it. Bypass can be risky because, unlike narrow bandwidth covert channels that are difficult to exploit, bypass can present a large, easily exploitable overt leak in the system. Bypass often arises out of failure to use trusted operating environments to maintain continuous separation of security domains all the way back to their origin. When that origin lies outside the system boundary, it may not be possible to validate the trusted separation to the origin. In that case, the risk of bypass can be unavoidable if the flow truly is essential.

A common example of unavoidable bypass is a subject system that is required to accept secret IP packets from an untrusted source, encrypt the secret userdata and not the header and deposit the result to an untrusted network. The source lies outside the sphere of influence of the subject system. Although the source is untrusted (e.g. system high) it is being trusted as if it were MLS because it provides packets that have unclassified headers and secret plaintext userdata, an MLS data construct. Since the source is untrusted, it could be corrupt and place secrets in the unclassified packet header. The corrupted packet headers could be nonsense but it is impossible for the subject system to determine that with any reasonable reliability. The packet userdata is cryptographically well protected but the packet header can contain readable secrets. If the corrupted packets are passed to an untrusted network by the subject system they may not be routable but some cooperating corrupt process in the network could grab the packets and acknowledge them and the subject system may not detect the leak. This can be a large overt leak that is hard to detect. Viewing classified packets with unclassified headers as system high structures instead of the MLS structures they really are presents a very common but serious threat.

Most bypass is avoidable. Avoidable bypass often results when system architects design a system before correctly considering security, then attempt to apply security after the fact as add-on functions. In that situation, bypass appears to be the only (easy) way to make the system work. Some pseudo-secure schemes are proposed (and approved!) that examine the contents of the bypassed data in a vain attempt to establish that bypassed data contains no secrets. This is not possible without trusting something about the data such as its format, which is contrary to the assumption that the source is not trusted to preserve any characteristics of the source data. Assured 'secure bypass' is a myth, just as a so-called High Assurance Guard (HAG) that transparently implements bypass. The risk these introduce has long been acknowledged; extant solutions are ultimately procedural, rather than technical. There is no way to know with certainty how much classified information is taken from our systems by exploitation of bypass.

'There is no such thing as MLS'[edit]

With the decline^[9] in COMPUSEC experts, more laypersons who are not COMPUSEC-astute are designing secure computing systems and are mistakenly drawing this conclusion because the term MLS is being overloaded. These two uses are: MLS as a processing environment vs MLS as a capability. The false conclusion is based on a belief that there are no products certified to operate in an MLS environment or mode and that therefore MLS as a capability does not exist. One does not imply the other. Many systems operate in an environment containing data that has unequal security levels and therefore is MLS by the Computer Security Intermediate Value Theorem (CS-IVT).^[10] The consequence of this confusion runs deeper. NSA-certified MLS operating systems, databases, and networks have existed in operational mode since the 1970s and that MLS products are continuing to be built, marketed, and deployed.

Laypersons often conclude that to admit that a system operates in an MLS environment (environment-centric meaning of MLS) is to be backed into the perceived corner of having a problem with no MLS solution (capability-centric meaning of MLS). MLS is deceptively complex and just because simple solutions are not obvious does not justify a conclusion that they do not exist. This can lead to a crippling ignorance about COMPUSEC that manifests itself as whispers that 'one cannot talk about MLS,' and 'There's no such thing as MLS.' These MLS-denial schemes change so rapidly that they cannot be addressed. Instead, it is important to clarify the distinction between MLS-environment and MLS-capable.

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• MLS as a security environment or security mode: A community whose users have differing security clearances may perceive MLS as a data sharing capability: users can share information with recipients whose clearance allows receipt of that information. A system is operating in MLS Mode when it has (or could have) connectivity to a destination that is cleared to a lower security level than any of the data the MLS system contains. This is formalized in the CS-IVT. Determination of security mode of a system depends entirely on the system's security environment; the classification of data it contains, the clearance of those who can get direct or indirect access to the system or its outputs or signals, and the system's connectivity and ports to other systems. Security mode is independent of capabilities, although a system should not be operated in a mode for which it is not worthy of trust.
• MLS as a capability: Developers of products or systems intended to allow MLS data sharing tend to loosely perceive it in terms of a capability to enforce intelligence database spanning the JWICS and SIPRNet networks. There is a project to create a labeled version of PostgreSQL, and there are also older labeled-database implementations such as Trusted Rubix. These MLS database systems provide a unified back-end system for content spanning multiple labels, but they do not resolve the challenge of having users process content at multiple security levels in one system while enforcing mandatory access controls.

  There are also several MLS end-user applications. The other MLS capability currently on the UCDMO baseline is called MLChat, and it is a chat server that runs on the XTS-400 operating system - it was created by the US Naval Research Laboratory. Given that content from users at different domains passes through the MLChat server, dirty-word scanning is employed to protect classified content, and there has been some debate about if this is truly an MLS system or more a form of cross-domain transfer data guard. Mandatory access controls are maintained by a combination of XTS-400 and application-specific mechanisms.^[12]

  Joint Cross Domain eXchange (JCDX) is another example of an MLS capability currently on the UCDMO^{[permanent dead link]} baseline. JCDX is the only Department of Defense (DoD), Defense Intelligence Agency (DIA) accredited Multilevel Security (MLS) Command, Control, Communication, Computers and Intelligence (C4I) system that provides near real-time intelligence and warning support to theater and forward deployed tactical commanders. The JCDX architecture is comprehensively integrated with a high assurance Protection Level Four (PL4) secure operating system, utilizing data labeling to disseminate near real-time data information on force activities and potential terrorist threats on and around the world's oceans. It is installed at locations in United States and Allied partner countries where it is capable of providing data from Top Secret/SCI down to Secret-Releasable levels, all on a single platform.

  MLS applications not currently part of the UCDMO baseline include several applications from BlueSpace. BlueSpace has several MLS applications, including an MLS email client, an MLS search application and an MLS C2 system. BlueSpace leverages a middleware strategy to enable its applications to be platform neutral, orchestrating one user interface across multiple Windows OS instances (virtualized or remote terminal sessions). The US Naval Research Laboratory has also implemented a multilevel web application framework called MLWeb which integrates the Ruby on Rails framework with a multilevel database based on SQLite3.

  Future[edit]

  Perhaps the greatest change going on in the multilevel security arena today is the convergence of MLS with virtualization. An increasing number of trusted operating systems are moving away from labeling files and processes, and are instead moving towards UNIX containers or virtual machines. Examples include zones in Solaris 10 TX, and the padded cell hypervisor in systems such as Green Hill'sIntegrity platform, and XenClient XT from Citrix. The High Assurance Platform from NSA as implemented in General Dynamics' Trusted Virtualization Environment (TVE) is another example - it uses SELinux at its core, and can support MLS applications that span multiple domains.

  See also[edit]

  • Biba model, Biba Integrity Model
  • Discretionary access control (DAC)
  • Evaluation Assurance Level (EAL)
  • Mandatory access control (MAC)
  • Multi categories security (MCS)
  • Non-interference (security) model
  • Role-based access control (RBAC)
  • Security modes of operation

  References[edit]

  1. ^Davidson, J.A. (1996-12-09). Asymmetric isolation. Computer Security Applications Conference. pp. 44–54. doi:10.1109/CSAC.1996.569668. ISBN978-0-8186-7606-2.
  2. ^CSC-STD-004-85: Computer Security Requirements - Guidance For Applying The Department Of Defense Trusted Computer System Evaluation Criteria In Specific Environments (25 June 1985)
  3. ^Multi-Level Security confidentiality policy in FreeBSD
  4. ^'Validated Product - Red Hat Enterprise Linux Version 5 running on IBM Hardware'. National Information Assurance Partnership, Common Criteria Evaluation and Validation Scheme, United States. June 7, 2007.Cite journal requires journal= (help)
  5. ^Controlled Access Protection Profile (CAPP)
  6. ^Corrin, Amber (2017-08-08). 'How BICES-X facilitates global intelligence'. C4ISRNET. Retrieved 2018-12-10.
  7. ^'Solaris 10 Release 11/06 Trusted Extensions'. Communications Security Establishment Canada. 2008-06-11. Archived from the original on 2011-06-17. Retrieved 2010-06-26.Cite journal requires journal= (help)
  8. ^'Security Target, Version 1.22 for XTS-400, Version 6.4.U4'(PDF). National Information Assurance Partnership, Common Criteria Evaluation and Validation Scheme, United States. 2008-06-01. Archived from the original(PDF) on 2011-07-23. Retrieved 2010-08-11.Cite journal requires journal= (help)
  9. ^David Elliott Bell: Looking Back at the Bell–LaPadula model - AddendumArchived 2011-08-27 at the Wayback Machine (December 20, 2006)
  10. ^David Elliott Bell: Looking Back at the Bell–LaPadula model (December 7, 2005)
  11. ^For example: Petersen, Richard (2011). Fedora 14 Administration and Security. Surfing Turtle Press. p. 298. ISBN9781936280223. Retrieved 2012-09-13. The SELinux reference policy [..] Multi-level security (MLS) adds a more refined security access method. MLS adds a security level value to resources.
  12. ^http://www.sse.gr/NATO/EreunaKaiTexnologiaNATO/36.Coalition_C4ISR_architectures_and_information_exchange_capabilities/RTO-MP-IST-042/MP-IST-042-12.pdf^{[permanent dead link]}

  Further reading[edit]

  • Lampson, B. (1973). 'A note on the confinement problem'. Communications of the ACM. 16 (10): 613–615. CiteSeerX10.1.1.129.1549. doi:10.1145/362375.362389.
  • NCSC (1985). 'Trusted Computer System Evaluation Criteria'. National Computer Security Center.Cite journal requires journal= (help) (a.k.a. the TCSEC or 'Orange Book').
  • NCSC (1986). 'Trusted Network Interpretation'. National Computer Security Center.Cite journal requires journal= (help) (a.k.a. the TNI or 'Red Book'). [1]
  • Smith, Richard (2005). 'Chapter 205: Multilevel security'. In Hossein Bidgoli (ed.). Handbook of Information Security, Volume 3, Threats, Vulnerabilities, Prevention, Detection and Management. New York: John Wiley. Archived from the original on 2006-05-06. Retrieved May 21, 2006.ISBN0-471-64832-9.
  • Patel, D., Collins, R., Vanfleet, W. M., Calloni, B. A., Wilding, M. M., MacLearn, L., & Luke, J. A. (November 2002). 'Deeply Embedded High Assurance (Multiple Independent Levels of Security/Safety) MILS Architecture'(PDF). Center for research on economic development and policy reform. Archived from the original(PDF) on April 28, 2003. Retrieved 2005-11-06.Cite journal requires journal= (help)CS1 maint: multiple names: authors list (link)
  • P. A. Loscocco, S. D. Smalley, P. A. Muckelbauer, R. C. Taylor, S. J. Turner, and J. F. Farrell. The Inevitability of Failure: The Flawed Assumption of Security in Modern Computing Environments. In Proceedings of the 21st National Information Systems Security Conference, pages 303–314, Oct. 1998. [2].

  External links[edit]

Apple Macs are less vulnerable to attack by malware than Windows PCs. Many people, in fact, believe that Macs are immune to viruses and spyware, but this is definitely not the case. As the use of Macs increases for both business and personal use, so does the malicious activity directed against them as criminals will reap a greater return.

• Do not assume that your Apple computers are safe from malware.
• Always have internet security software loaded, updated and switched on.

Many other subjects on this website are common to Macs and these should also be read if you want to keep your Mac safe.

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This article covers Mac OS X but not earlier Mac operating systems. For maximum security, we recommend upgrading to the latest version.

The risks

• Viruses, spyware and other malware.
• Attacks by hackers attempting to obtain personal or financial information.
• Physical loss of hardware due to theft, carelessness, fire/flood and other natural disaster.

Protecting your Mac

Keep your software up to date

Apply security updates and system software upgrades as soon as they become available. And remember that a Mac can carry a virus and pass it to other computers even if it is not affected itself.

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• Check for updates by going to the System Preferences application and selecting Software Update and clicking Check Now.
• Make sure Check for Updates is ticked and Daily is selected in the drop-down menu. This will ensure that your computer automatically checks every day for new updates. You will need to provide an Administrator password to enable this feature.
• To check manually for updates, go to the Apple menu (the small Apple icon in the top left corner) and select Software Update. This check should be performed regularly.
• Software purchased through the Apple Store will also checked for updates.
• Check third-party software manufacturers’ websites regularly for application updates. Microsoft updates can be downloaded from www.microsoft.com/mac/downloads

Switch on your firewall

• Open the System Preferences application and click on Security; click on Firewall and click Start.

Internet security software

• Ensure you always have effective and updated internet security software loaded and running. Most internet security software suppliers sell packages and individual solutions specifically designed for Macs. There are also many free internet security products available.

Backups

The information held on your Mac may be irreplaceable. Regularly backing up your data will ensure that you have more than one copy.

iCloud is Apple’s secure online backup and storage solution. It stores music, photos, video and documents and makes the files available to all your Apple devices – Macs, iPhones and iPads. iCloud is ideal for many users who do not require significant data storage volumes, offering a free storage limit of 5GB. Additional storage is charged annually according to the volume of date stored. iCloud backups are incremental, so while the first backup may take some time, subsequent backups will be faster, automatically uploading only data which has changed since the previous backup.

Because of the cost of backing up your data to iCloud – or if you have a slow or no internet connection – you may wish to consider backing up to a local, external hard drive manufactured by Apple and a number of other suppliers. Macs feature a built-in utility called Time Machine which creates incremental backups of files that can be restored at a later date. It also allows you to restore the whole system (power on your Mac and hold down the Command (⌘) and R keys when the gray screen appears or boot from the OS X Install DVD), multiple files, or a single file.

Further advice and tips

• Use strong passwords and update them regularly. From OSX 10.9 (Mavericks), the Keychain built-in password/login manager can detect when you are filling in a login or registration form in Safari. It will then offer you a strong password that you can use and store in your keychain. This process is explained in more detail on a number of websites, for example: www.imore.com/how-generate-password-icloud-keychain-and-os-x-mavericks
• Mac OS X disables the root user by default. It should never be enabled.
• For additional security go to the System Preferences application, select Security and tick each of the options on the bottom half of the screen: Require password to wake this computer from sleep or screen saver; Disable automatic login; Require password to unlock each secure system preference; Log out after 10 minutes of inactivity; and Use secure virtual memory. Most of these options relate to controlling access to the computer by unauthorised users.
• Consider encrypting your files in case your computer is stolen, especially if you are using a MacBook, MacBook Pro or MacBook Air. It will prevent your files being read. To do this, go to the System Preferences application, select Security and Turn on FileVault. Be aware, however, that enabling FileVault will affect how Time Machine backs up your user data.
• If you use virtualisation software such as Boot Camp, Parallels or VirtualBox to run a Windows system, you should make sure that it is secured as if it were a regular PC.
• If your Mac is shared by different users, set up user accounts and passwords so that private files are kept separate and the ability to reconfigure security settings on the computer are restricted. To do this, go to the System Preferences application and select Accounts. Follow the instructions to add new users and set up parental controls and other restrictions.
• Create a single ‘main’ administration account. You should not need to log in to this account regularly, but you will need to remember the account name and password. Regular user accounts should have the ‘Allow user to administer this computer’ option unchecked.
• Create a ‘Hot Corner’ to start your screen saver (provided you have set the screen saver option to always request a password). Start System Preferences, and select the ‘Desktop & Screen Saver’ section. At the bottom right is the ‘Hot Corners’ button. Select your preferred corner and select ‘Start Screen Saver’ from the drop-down menu.
  Now you can start the screen saver simply by rolling the mouse to the relevant corner of the screen.