Applying default deny to real life

Friday, June 25th, 2010 at 07:49pm

Default deny is the security stance where anything that is not explicitly permitted, is forbidden. I use it all the time when writing code: extra form fields, ignore them, input doesn’t match, reject it, etc. It also fits in very nicely with defensive programming.

The opposite stance is default permit, number one of the six dumbest ideas in computer security.

In many aspects of my life I have been applying default permit. For example I used to buy up any vintage apple parts that were listed on ebay and I couldn’t walk past a secondhand book sale without buying a big handful of books.

Almost a year ago when I decided to downsize my computer collection I switched from default permit to default deny. I did this by starting to think about which items I wanted to keep, not about which items I could discard. The downsizing has continued in fits and starts, in some areas further than I had intended last year as I no longer have any PowerBooks or Newtons.

My other example above was books. I have a lot of books, specifically paperback novels, a mixture of fantasy, science fiction and action. But I have too many. Specifically too many to fit on the shelves so that they are doubled up.

A few weeks ago while listing some Apple parts on eBay I found that I was able to list items for free, so I grabbed quite a few books, photographed them and listed them. The books I selected first were mostly action and included a lot of spin-offs that were being mostly written by a secondary author, because of this I couldn’t see myself reading these books for a second time. Example of these include The Dreamers by David Eddings, the Dale Brown Dreamland collaborations, and Tom Clancy’s Net Force,

In hindsight this was default permit. I am going to get rid of a lot more books, but this time I will apply default deny. This means I will start by making a list of the books that I will read multiple times. This is a much smaller selective group that could contain everything by an author (Terry Pratchett is a clear candidate), or selected works from an author (early David Eddings, short story collections from Frederick Forsyth, Jeffrey Archer and Philip K. Dick).

Of course I will attempt to apply default deny to everything, not just computers and books, but I expect it will take time…

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