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Privacy With a 4096 Bit RSA Key — Offline, On Paper
HavanaF writes "Online backup is practical, but can it offer any privacy? The Dutch security company Safeberg developed an Offline Private Key Protocol, with an asymmetric key scheme. The protocol demands that the private (decryption) key be stored away from the 'source' computer, which presumably is 'too vulnerable.' The catch is that the private key needs to be fairly large to be secure: a 4,096-bit RSA key should suffice for some years. But how to store an 800-character key offline? Safeberg introduces a machine readable paper key, with the 4k-bit key crammed in a giant 2D Datamatrix barcode. This video on key strength tells the story."
Bar codes printed on media of all kinds are generally quite robust and not error prone. The printing device does not need to be special in any way. The reader does not need to be special in any way. Print the key on acid-free paper using a laser printer and store it for a looong time. I'll leave it up to the slashdot tifosi to declare how long it would last in a bank vault.
Some nice ways to encode keys and store it as a symbol on paper here: http://www.adams1.com/stack.html
Symbology is very non-sexy knowledge, but valuable in logistics.
http://www.maxineudall.com/2010/02/should-economists-be-sued-for-malpractice.html
Reading numbers is more error prone. With the bar code, there are presumably lots of check digits and other such loveliness encoded into it.
As for folding it, what happens? Probably nothing. There are usually CRCs (or similar) and lots of other stuff in those 2D bar codes. This particular scheme, Data Matrix, is apparently highly redundant, allowing full recovery of the data even if (up to) 30% of the bar code is destroyed.
http://www.tlashford.com/TLA/pages/Basic_sym/Symbol_overview.htm#DATAMATRIX
http://en.wikipedia.org/wiki/Data_matrix_(computer)
Check out my sci-fi/humor trilogy at PatriotsBooks.
No offense, but this information is wrong. Data Matrix is completely unencumbered by patents. For one thing, it was released into the public domain by its inventor, and for another it's so old that even if there had been patents they would have expired by now.
There was one "IP" company that made some noise in 2006-2007 claiming to cover some of the underlying technology in their patent portfolio, but they were handed their hats in court. I followed the issue very closely, even stopping distribution of my Data Matrix open source project for a while, pending this outcome. But rest assured that Data Matrix is unencumbered by patents and safe to use in your projects.