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Sunday, December 14, 2008

Paper shredder,Unshredding,Forensic identification,residential shredders

Paper shredders are used to cut paper into chad, typically either strips or fine particles. Government organizations, businesses, and private individuals use shredders to destroy private, confidential, or otherwise sensitive documents. Privacy experts often recommend that individuals shred bills, credit card and bank account statements, and other documents which could be used by thieves to commit fraud or identity theft.


The first paper shredder is credited to prolific inventor Abbot Augustus Low of Horseshoe, New York. His patent for a “waste paper receptacle” to offer an improved method of disposing of waste paper was filed on February 2, 1909 and received the U.S. patent number 929,960 on August 31, 1909. Low’s invention was never manufactured, however.

Adolf Ehinger's paper shredder, based on a hand-crank pasta maker, was manufactured in 1935 in Germany. Supposedly he needed to shred his anti-Nazi propaganda to avoid the inquiries of the authorities. Ehinger later marketed his shredders to government agencies and financial institutions converting from hand-crank to electric motor. Ehinger's company, EBA Maschinenfabrik, manufactured the first cross-cut paper shredders in 1959 and continues to do so to this day as EBA Krug & Priester GmbH & Co. in Balingen.

The U.S. embassy in Iran used strip-cut paper shredders to reduce paper pages to strips before the embassy was taken over in 1979 (not entirely successfully, see below the section on "unshredding"). After Colonel Oliver North told Congress that he used a Schleicher Intimus 007 S cross-cut model to shred Iran-Contra documents, sales for that company increased nearly 20 percent in 1987.

Until the mid-1980s, it was rare for paper shredders to be used by non-government entities. After the 1984 Supreme Court decision in California v. Greenwood, in which the Supreme Court of the United States held that the Fourth Amendment does not prohibit the warrantless search and seizure of garbage left for collection outside of a home, paper shredders became more popular among US citizens with privacy concerns. Anti-burning laws, concern over landfills, industrial espionage, and identity theft concerns created greater demand for paper shredding.

Shredding at high levels continues in government agencies too. According to the report of the Paul Volcker Committee, between April and December 2004, Kofi Annan’s then Chef de Cabinet Iqbal Riza authorized thousands of UN documents shredded including the entire chronological files of the Oil-for-Food Programme between the years 1997-1999.
Multi-cut scissors used to shred paper

Types of shredders

Shredders range in size and price from small and inexpensive units meant for a few pages, to large units used by commercial shredding services that costs hundreds of thousands of dollars and can shred millions of documents an hour. Some shredders used by a commercial shredding service are built into a shredding truck.

The normal small shredder is an electrically powered device, but there are unpowered ones such as special scissors with multiple blade pair and shredders which are hand-cranked.

These machines are classified according to the size and shape of the shreds they produce. (As a practical matter, this is also a measure of the degree of randomness or entropy they generate.) Shredders can range in size from standard scissors and other hand-operated devices all the way up to truck-sized shredders.

* Strip-cut shredders, the least secure, use rotating knives to cut narrow strips as long as the original sheet of paper. Such strips can be reassembled by a determined and patient investigator or adversary, as the product (the destroyed information) of this type of shredder is the least randomized. It also creates the highest volume of waste inasmuch as the chad has the largest surface area and is not compressed.
* Cross-cut or confetti-cut shredders use two contra-rotating drums to cut rectangular, parallelogram, or diamond-shaped (or lozenge) 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 pound the paper through a screen.
* Pierce and Tear Rotating blades pierce the paper and then tear it apart.
* Grinders A rotating shaft with cutting blades grinds the paper until it is small enough to fall through a screen.

Historically, the General Services Administration (GSA) set paper shredder guidance in the Interim Federal Specification FF-S-001169 dated July 1971 which was superseded by standard A-A-2599 for classified material which was canceled in February 2000. GSA has not published a new standard since.

There are also alternative shredders that use burning, chemical decomposition, or composting for disposing of the shreds.
Paper shredding can be contracted out

Shredder trucks

A mobile shredding truck is a box truck with an industrial sized paper shredder mounted inside the box, typically in the front section of the box, closest to the cab. The box is divided into two sections: the shredding equipment area, and the payload area for storage of the shredded materials. These trucks have been designed to shred up to 8,000 lbs of paper an hour. Mobile shredding trucks can have a shredded material storage capacity of 6,000 to 15,000 pounds of shredded paper. Office paper is the typical material being shredded, but with increasing security concerns customers also request shredding of CDs, DVDs, hard drives, credit cards, and uniforms, among other things. There are many manufactures for mobile shredding trucks, while only a few are among those that design equipment in house.

Shredding services

Due to information privacy laws like FACTA, HIPAA and the Gramm-Leach-Bliley Act the volume of shredding at the typical business has increased dramatically. Some companies outsource their shredding to shredding services. These companies either shred on-site, with mobile shredder trucks or have off-site shredding facilities. Some mobile shredding companies then send the shredded paper to a paper mill where it is recycled.


In some cases it is technically possible to reassemble the pieces of shredded documents; the feasibility of such a project is a cost-to-benefit calculation. If the chad is not further randomized, the "noodles" that belonged to the same document tend come out of the shredder close to each other and remain roughly in that configuration. Furthermore, when the documents are fed to the shredder in a way that the lines of text are not perpendicular to the shredder blades, portions of text may remain legible on the stripes.
Wikisource has original text related to this article:
Documents Seized from the US Embassy in Tehran

Shredded documents can be reassembled manually. After the Iranian Revolution and the takeover of the U.S. embassy in Tehran in 1979, Iranians enlisted local carpet weavers who reconstructed the pieces by hand. The recovered documents would be later released by the Iranian regime in a series of books called "Documents from the US espionage Den". The US government subsequently improved its shredding techniques by adding pulverizing, pulping, and chemical decomposition protocols.

Modern computer technology considerably speeds up the process of reassembling shredded documents. The strips are scanned on both sides, and then the computer determines how the strips should be put together. Robert Johnson of the National Association for Information Destruction, has stated that there is a huge demand for document reconstruction. Several companies offer commercial document reconstruction services. For maximum security, documents should be shredded so that the words of the document go through the shredder horizontally (i.e. 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. There is currently an effort underway to recover the shredded archives of the Stasi, the East German secret police. There are "millions of shreds of paper that panicked Stasi officials threw into garbage bags during the regime's final days in the fall of 1989". As it has taken three dozen people six years to reconstruct 300 of the 16,000 bags, the German government is considering modern computerized methods of reconstruction.

Forensic identification

Document shredders display certain device-specific characteristics, "fingerprints", like the exact spacing of the blades, the degree and pattern of their wear. 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 individual shredder that was used to destroy a given document may be determined. Jack Brassil, a researcher for Hewlett-Packard, works on a project for making shredders more easily traceable. (Cf. the forensic identification of typewriters.)

Injury risk with residential shredders

As with any motorized cutting equipment, there is a risk of injury. Small residential shredders are becoming more and more common. These shredders, although designed with a narrow opening to the cutting wheels, still pose a danger to pets and small children. Many home shredders can be left in a "stand-by" mode that will start the cutting process when anything is inserted into the feed slot. In homes with small children or pets, simply keeping the shredder unplugged while not in use can greatly reduce any risk. Many new shredders on the market now feature improved safety features.


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