311324054-Computer-Security-Cheat-Sheet.docx - Security...

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Security Principles Security is economics . No system is completely, 100% secure against all attacks. Rather, systems may only need to resist a certain level of attack. There is no point buying a $10,000 firewall to protect $1,000 worth of trade secrets. Ex: safes Least privilege . Give a program the set of access privileges that it legitimately needs to do its job—but nothing more. Try to minimize how much privilege you give each program and system component Use fail-safe defaults. Use default-deny polices. Start by denying all access, then allow only that which has been explicitly permitted. Ensure that if the security mechanisms fail or crash, they will default to secure behavior, not to insecure behavior. Separation of responsibility . Split up privilege, so no one person or program has complete power. Require more than one party to approve before access is granted. Ex: two launch officers must agree before the missile can be launched. Defense in depth. If you use multiple redundant protections, then all of them would need to be breached before the system’s security will be endangered. Psychological acceptability . It is important that your users buy into the security model. Example: Suppose the company firewall administrator gains a reputation for capriciously, for no good reason, blocking applications that the engineers need to use to get their job done. Pretty soon, the engineers are going to view the firewall as damage and route around it Human factors matter . Security systems must be usable by ordinary people, and must be designed to take into account the role humans will play. Example: Your web browser pops up security warnings all the time, with vague alarming warnings but no clear indication of what steps you can take and no guidance on how to handle the risk. If you’re like most of the user population, you’re soon going to learn to always click “Ok” any time a security dialogue box pops up. Ensure complete mediation . When enforcing access control policies, make sure that you check every access to every object. Know your threat model . Be careful with old code. The assumptions originally made might no longer be valid. The threat model may have changed.
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