CHAPTER 4 © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT Forsharing SALE OR DISTRIBUTION Files NOT for SALE OR DISTRIBUTION
Total Page:16
File Type:pdf, Size:1020Kb
© Jones & Bartlett Learning,© Jones LLC & Bartlett Learning LLC, an Ascend Learning© Jones Company. & NOT Bartlett FOR SALE Learning, OR DISTRIBUTION. LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC © Digital_Art/ShutterstockNOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION CHAPTER 4 © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FORSharing SALE OR DISTRIBUTION Files NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION ▸ About This Chapter In this chapter, we work with the mechanisms provided by operating systems like Unix and Windows to protect files and folders. We also take a technical look at the fifth phase© of Jones the security & Bartlettprocess: monitoring Learning, the system. LLC The chapter focuses on © Jones & Bartlett Learning, LLC these topics:NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION ■ Tailoring the security policy to grant special access to individuals or groups ■ Permission flags in Unix-like systems ■ Access control lists in Macintosh and Windows systems ■ © Jones &Monitoring Bartlett system Learning, events through LLC logging © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION ▸ 4.1 Controlled Sharing What happens if Bob needs to share files with one or two other users but not with the rest of the suite? © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTIONBob hired a clerk to do data entry for his newNOT client, FOR a big SALE surveying OR com- DISTRIBUTION pany. The new clerk, Tina, has her own login on Bob’s computer (“tina”). However, the isolation policy blocks Bob and Tina from sharing files, unless Bob logs in as administrator and bypasses the access restrictions. It is clear© Jones that we &can Bartlett create files Learning, and folders andLLC establish access rights for © Jones & Bartlett Learning, LLC them. We NOTcan share FOR files SALEwith some OR people DISTRIBUTION and hide them from others, simply by NOT FOR SALE OR DISTRIBUTION configuring the right permissions. In small cases we might get this correct through trial-and-error, but we might also leak data while implementing our solution. Instead, we begin with identifying our objectives, threats, risks, and requirements. We plan and implement our controls based on the requirements. © Jones &When Bartlett we write Learning, the requirements LLC and policy, we want to capture© Jones our general & Bartlett Learning, LLC NOT FORintent. SALE When we OR write DISTRIBUTION up implementation details, we get specific.NOT In this FOR case, SALEthe OR DISTRIBUTION © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning,© Jones LLC & Bartlett Learning LLC, an Ascend Learning© Jones Company. & NOT Bartlett FOR SALE Learning, OR DISTRIBUTION. LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION 136 Chapter 4 Sharing Files requirements talk about people and general types of information (Bob, Tina, and © Jonesshared & bookkeepingBartlett Learning, data). Implementation LLC controls talk about files,© Jones folders, users, & Bartlett Learning, LLC NOT FORand access SALE rights. OR Here DISTRIBUTION are the two requirements we add to our isolationNOT FOR policy: SALE OR DISTRIBUTION ■ Bob and Tina shall be able to read and modify the surveying company’s bookkeeping data. ■ No one shall have access to bookkeeping data, except Bob and Tina. © Jones & Bartlett Learning,Although globalLLC restrictions like “no one ©shall” Jones are sometimes & Bartlett hard toLearning, verify, LLC accurate policy statements may require them. NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Tailored File Security Policies To share the project files, Bob needs to adjust his user isolation security policy. Practical problems like this often arise when using one-size-fits-all policies like © Jones & Bartlett Learning, LLC“isolate everyone” or “share© everything.” Jones & We Bartlett address Learning,such things with LLC tailored NOT FOR SALE OR DISTRIBUTIONaccess policies. Three examplesNOT of tailoredFOR SALEpolicies are:OR DISTRIBUTION 1. Privacy 2. Shared reading 3. Shared updating © Jones &We Bartlett can describe Learning, a tailored policy LLC in several ways. Here we ©take Jones a systematic & Bartlett Learning, LLC NOT FORapproach. SALE We implementOR DISTRIBUTION each tailored policy underneath a systemwideNOT FOR default SALE OR DISTRIBUTION policy of either isolation or sharing. The tailored policy specifies additional access rights. These new rights may add to or replace the default rights. For each new set of rights, the tailored policy needs to consider four things: © Jones & Bartlett 1.Learning, Which files LLC or other resources are involved© (e.g.,Jones files relating& Bartlett to “Surveyors” Learning, LLC NOT FOR SALE OR DISTRIBUTIONor perhaps “Tina’s personal files”)? NOT FOR SALE OR DISTRIBUTION 2. Which users are granted these new rights (e.g., users editing the books for “Surveyors”)? 3. Do we Deny by Default, or do we retain the default access rights for these files? © Jones & Bartlett Learning, LLC4. Which access rights do we© enforce:Jones full & access,Bartlett execute, Learning, read-only, orLLC no access? NOT FOR SALE OR DISTRIBUTIONTypically, the files in questionNOT willFOR reside SALE within OR a particular DISTRIBUTION directory and be used by a particular group of people. When we describe the policy, however, we must be careful to describe what we want, rather than how we’ll do it. © JonesBob’s & BartlettSharing Learning, Dilemma LLC © Jones & Bartlett Learning, LLC NOT FORBob needs SALE to implement OR DISTRIBUTION a tailored updating policy so that he canNOT share FOR files with SALE OR DISTRIBUTION Tina. But how should he do it? For each file, we can control access by the owner, administrators, and the rest of the users. If that’s all we have, there’s no way to grant access to two specific users while blocking access to the rest. © Jones & Bartlett Learning,Bob could LLCsolve this sharing dilemma if he© always Jones logs &in toBartlett a system adminisLearning,- LLC NOT FOR SALE ORtration DISTRIBUTION account. On some systems, these accountsNOT use FOR a specific SALE user identityOR DISTRIBUTION with a name like “system” or “root” that receives all system-related access rights. If Bob does this, the account will have full access to Tina’s files. If he wants to create files © Jones & Bartlett Learning, LLC © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION © Jones & Bartlett Learning,© Jones LLC & Bartlett Learning LLC, an Ascend Learning© Jones Company. & NOT Bartlett FOR SALE Learning, OR DISTRIBUTION. LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION 4.1 Controlled Sharing 137 to share with Tina, however, he must make Tina the owner of those files. Other- wise, he wouldn’t© Jones be able & toBartlett restrict access Learning, exclusively LLC to Tina and himself. © Jones & Bartlett Learning, LLC This NOTsolution FOR poses SALE a problem: OR Least DISTRIBUTION Privilege. It may seem convenient to NOT FOR SALE OR DISTRIBUTION log into a system routinely as “root” or some other administrative identity, but it poses a real risk to the system. If Bob unexpectedly exposes the system to a virus or malicious website while using administrative privileges, the system may quickly become compromised. © Jones &We Bartlett can solve Learning,Bob’s problem LLC if we can specify additional ©access Jones rights & for Bartlett Learning, LLC NOT FOReach file SALE and folder. OR DISTRIBUTIONThere are two choices, depending on whichNOT operating FOR sys SALE- OR DISTRIBUTION tem we use: 1. Keep a list of access rights for each file, called the access control list (ACL). Each entry in the ACL identifies a specific user and contains a list of access rights granted to that user. This is available on modern versions of Windows © Jones & Bartlett Learning,and on Apple’s LLC MacOS. © Jones & Bartlett Learning, LLC NOT FOR SALE OR2. DISTRIBUTIONKeep one additional set of access rights, andNOT associate FOR it SALEwith a user OR group DISTRIBUTION. Associate a group with each file, just as we associate a user, the owner, with each file. This is available on all Unix-based systems. Windows uses a simple version of ACLs to provide basic file sharing on “home” editions© Jones of Windows. & Bartlett All Unix-based Learning, systems LLC provide group-based access © Jones & Bartlett Learning, LLC controls. NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION Practical Tip: Always organize your files into separate folders according to their access rights. Bob and Tina need to share the bookkeeping files for the surveying company. They put the files they need to share into a specific folder. They set up the folder’s access rights to let them share the © Jones &files. Bartlett Neither BobLearning, nor Tina shouldLLC store files in that folder© unless Jones both & Bartlett Learning, LLC NOT FORof SALE them should OR DISTRIBUTIONbe sharing that file. If Bob hires another clerkNOT to FORwork SALE OR DISTRIBUTION on a different customer’s books, he should set up a separate folder for that clerk. © Jones & Bartlett 4.1.1Learning, Basic LLC File Sharing on Windows© Jones & Bartlett Learning, LLC NOT FOR SALE ORWindows DISTRIBUTION provides a very simple mechanism NOTfor sharing FOR files SALE among OR users DISTRIBUTION on a personal computer. The mechanism begins with an isolation policy; users have no access to other users’ personal files. Building on the isolation policy, we assign additional permissions to selected users. To implement tailored sharing, we put the files in a folder and enable file shar- ing for that© folder. Jones File &sharing Bartlett recognizes Learning, three sets LLC of access rights: © Jones & Bartlett Learning, LLC NOT FOR SALE OR DISTRIBUTION NOT FOR SALE OR DISTRIBUTION 1.