A white box, in contrast to a black box, is a subsystem whose internals can be viewed, but usually cannot be altered.
Having access to the subsystem internals in general makes the subsystem easier to understand, but also easier to hack; if a programmer, for example, can examine source code, weaknesses in an algorithm are much easier to discover. This makes white box testing much more effective than black box testing, but considerably more difficult due to the sophistication needed on the part of the tester to understand the subsystem.
Also known as glass box, clear box, or open box.
In practice some white box systems are so complex that it might as well be a Black box.
Famous quotes containing the words white and/or box:
“Let us then suppose the Mind to be, as we say, white Paper, void of all Characters, without any Ideas; How comes it to be furnished...? To this I answer, in one word, From Experience: In that, all our Knowledge is founded; and from that it ultimately derives it self.”
—John Locke (1632–1704)
“I shall return in the dark and be seen,
Be led to my own room by well-intentioned hands,
Placed in a box with a lid whose underside is dark
So as to grow....”
—John Ashbery (b. 1927)