Paper shredder
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Image:Paper Shredder.JPG Image:Paper shredding lorry.jpg
Paper shredders are used to cut paper into very fine strips or tiny paper chips. This is usually done by individuals or organizations to destroy confidential documents in such a manner that they are very difficult to read. Privacy experts often recommend that individuals shred bills, account statements, and other documents from those who would use the items to commit fraud or identity theft.
However, careless users of cheaper shredders can have their privacy violated despite this precaution. For instance, if a person simply shreds the documents and does nothing else beyond putting it in the garbage, all the shredded pieces can be collected by an investigator. Once collected, they can be reassembled in an attempt to discover the content of the documents (see Unshredding). For maximum security, documents should be shredded so that the words of the document go through the shredder horizontally, perpendicular to the blades. Many of the documents in the Enron accountancy scandal were fed through the shredder the wrong way, making them easier to reassemble.
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Construction
Most paper shredders come with a waste basket of their own. Those that don't are built to fit over another waste basket. They range in size and price from small and inexpensive units meant for home use, to larger units used in business settings that cost several hundred dollars.
These machines are classified according to the size and shape of the waste they produce.
- Strip-cut shredders use rotating knives to cut narrow strips as long as the original sheet of paper. These strips can be reassembled by a determined investigator, so this type of shredder is the least secure. It also creates the highest volume of waste.
- Cross-cut shredders use two contra-rotating drums to cut rectangular or parallelogram-shaped shreds.
- Particle-cut shredders create tiny square or circular pieces.
- Disintegrators and granulators repeatedly cut the paper at random until the particles are small enough to pass through a mesh.
- Hammermills and pulverizers reduce the paper to dust using a combination of rotating and stationary blades.
There are numerous standards for the security levels of paper shredders, including:
- DIN 32757
- Level 1 = 12 mm strips
- Level 2 = 6 mm strips
- Level 3 = 2 mm strips (Confidential)
- Level 4 = 2 x 15 mm particles (Commercially Sensitive)
- Level 5 = 0.8 x 12 mm particles (Top Secret or Classified)
- Level 6 = 0.8 x 4 mm particles (Top Secret or Classified)
- United States Department of Defense (DoD)
- Top Secret = 0.8 x 11.1 mm (1/32" × 7/16") (= Federal Specification F-S-001169 ?)
- United States NSA/CSS 02-01 = 1 × 4 mm
There are also alternative shredders that use burning, chemical decomposition, or composting for disposing of the shreds.
After the Supreme Court decision in California v. Greenwood, paper shredders became popular among even ordinary Americans as a tool for privacy enforcement.
Unshredding
It is possible to reassemble the pieces of the documents. If the shreds are not disturbed, the noodles or particles that belonged to the same document tend to stay in proximity, though the smaller the shreds are the better they mix. Furthermore, when the documents are fed to the shredder in a way that the lines of text are not perpendicular to the shredder blades, longer parts of text remain legible on the stripes.
Shredded documents can be reassembled even manually. After the Iranian Revolution and the takeover of the U.S. embassy in Tehran in 1979, Iranians enlisted local carpet weavers, who, with patience developed in generations of tying 400 knots per inch, reconstructed the pieces by hand. The result was an update of shredding techniques used by the United States government to include pulverizing, pulping, and chemical decomposition, but these methods are not always available in emergencies.
Modern computer technology considerably speeds up the process. The strips get scanned from both sides, then the computer tries to find obvious matches, and only requires human attention when it can not reliably decide on its own. Several companies already offer commercial document reconstruction services, for example the Houston based ChurchStreet Technology, which developed their process as a response to the demand sparkled by the collapse of the Enron Corporation. As of 2003, ChurchStreet charged roughly $2,000 for a cubic foot of strip-shreds, and $8,000-$10,000 of cross-shreds of standard size of 1/32 × 7/16 inch (0.8 × 11.1 mm) strips, and its clients are largely law agencies and private law firms. According to Robert Johnson of the National Association for Information Destruction, the demand is huge.
Another data recovery effort underway is the reconstruction of shredded archives of East-German Stasi. [1]
Apparently some identity theft rings are enlisting methamphetamine users to unshred documents; the drug gives the users the patience to reassemble documents by hand, with no need for sleep. [2]
Forensic identification
The shredders display certain device-specific characteristics, "fingerprints", like the exact spacing of the blades, the degree and pattern of their wear, etc. These can be reconstructed from the minute variations of size of the paper strips and the microscopic marks on their edges, and by comparison with the strips produced by known shredders, the shredder that was used to destroy a given document may be traced back to. Jack Brassil, a researcher for Hewlett-Packard, works on a project for making shredders better traceable. (Cf. the forensic identification of typewriters.)