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+# Computer Security - lesson 6
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+#### Federico Maggi
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+###### 7 April 2016
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+## Software Security
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+
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+There is nothing really __secure__, there is something __secure enough__.
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+__Software security__ is a problem of design, but designing a software
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+in a secure way is __very hard__.
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+An unmet specification about security is a __security issue__.
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+
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+## Disclosure
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+Until the end of 1990' software vulnerabilities were not disclosed,
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+instead they were traded between security experts or they were sold.
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+At one point people began using __full disclosure__ to press software
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+vendors to fix vulnerabilities, that consists in making public information
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+about the vulnerabilities so that the vendors were forced to fix it
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+before someone takes advantage of it.
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+
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+## Anti Disclosure
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+After the full disclosure movement vendors realizes that offering visibility
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+to people disclosing bugs was a way of making them work for you instead of
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+against you, But then a new movement rose: the __Anti full disclosure__
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+that states that after the peoples gained visibility they have no
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+more reasons of giving vulnerabilities for free.
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+And this made the security expert role a paid job.
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+
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+The last developement in the sector was the introduction of __bug bounties__
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+
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+## Principles of secure design
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+- KISS
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+- Discard privileges as soon as possible
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+- Open design
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+- Concurrency and race conditions: __race conditions__ is an entire category of issues.
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+
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+## Key Issues of secure design
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+- fail-safe and default deny: programs should __fail-close__ and not fail-open
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+- use of shared-resources or untrusted libraries
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+- filter the input and outputs
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+- don't write crypto code, use tested libraries.
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+
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+## Conclusion
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+Volnerabilities may be __dense__ so taking out one vulnerability does not make the software
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+more secure.
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