3.1 Why Does Good Design Matter?
There is no question that resolving
security issues during the design phase of software is ideal from a
developer's point of view. Our experience (confirmed
by recent academic studies) shows that investing in design also makes
good business sense. To make this principle more tangible,
let's try to calculate the cost to fix a security
shortcoming at design time—as opposed to doing it as part of
implementation, during testing, or via a software patch. Research
reveals the following ratios, illustrated by Figure 3-1:
If the cost at design time is taken as a unit of 1, the
cost of fixing the same bug in
implementation is about 6.5 times as great. If the security vulnerability is caught at testing time, the cost is
15 times as great. If the security vulnerability has to be
patched after the
software is released—which means that the fix itself will have
to be released as a patch—the cost is about 60 times what it
would have cost to fix the problem at the design stage.
These figures argue strongly the case for being careful during
design. Keep in mind, too, that, as the study we just cited points
out, there are intangible costs as well: loss of goodwill,
reputation, and functionality, and more stress for everyone involved
in the project are common outcomes.
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