Forwarded From: phreak moi <hackerelitet_private> http://www.nytimes.com/library/tech/98/10/circuits/articles/08driv.html What's on Your Hard Drive? If You Want Privacy, It Pays to Find Out What Data Your Computer Saves And How to Erase Information That the Delete Button Hardly Touches By PETER H. LEWIS For computer users, some of the more startling revelations in the Starr report have nothing to do with sex. Footnotes in the report from the Office of the Independent Counsel include such phrases as "document recovered from Ms. Lewinsky's home computer," "e-mail retrieved from Catherine Davis's computer" and "deleted file from Ms. Lewinsky's home computer." One of the ways Kenneth W. Starr's investigators peered into the private lives of their subjects was to peer into their computers. What they were able to find, and the ease with which they found it, may prompt computer users to re-evaluate their computer practices. Word processing software, Web browsing software and electronic mail have become integral to all sorts of communications, both professional and personal. As a result, many people have files on their hard disks that they wish to keep private, like love letters, confidential business documents or financial data. And many people have sensitive, confidential and potentially embarrassing files in their computers that they do not know are there, either because they think that the files have been erased or because they are unaware that certain common programs on the computer automatically keep a log of what the user does. "Recovering files that were deleted from a computer directory is a trivial process," said Joel R. Reidenberg, a professor at the Fordham University School of Law in New York who specializes in privacy issues. He said a related issue was the computer's creation of sensitive files that the user often did not know were there in the first place. "The user's Web browser will create files, unbeknownst to the user, that record all their interactions," Professor Reidenberg said. "Many people today know about cookie files, but the browser creates a history file as well that keeps a record of the Web sites the user visits. And then there's a cache file that sometimes even keeps copies of the pictures that have been downloaded." More obscure are the temporary files created by word processors, for example, and the so-called swap files that an operating system creates as a way to manage computer memory. These files often remain readable even if the original files are erased. In computers, being safe can sometimes lead to being sorry, as Oliver L. North discovered in the Iran-contra investigation in the Reagan Administration, when incriminating files he thought had been deleted were later resurrected from network backup tapes. In the current Justice Department investigation of the Microsoft Corporation, e-mail messages and memorandums from long ago are being resurrected from computer disks and cited as crucial evidence. The great majority of computer users have little reason to believe that their computer files will be scrutinized by law-enforcement agents, corporate and government spies, or even special investigators. But what about unscrupulous co-workers or curious children or computer thieves? What confidential information resides on the hard disk of the computer that was donated to charity, sold at a yard sale or accidentally left on the commuter train? Examples abound of sensitive information going out the door when government agencies, pharmacies, doctors' offices and other businesses donate or sell used computers without erasing the computers' memories. Last year, for example, a woman in Nevada bought a used computer from an Internet auction company and was surprised to find that it contained names, addresses, Social Security numbers and prescription information for 2,000 people, including people being treated for AIDS, alcoholism and mental illnesses. A pharmacy had failed to erase the information when it sold the computer. The rise in the number of computer thefts and the increased sharing of computers in the home are confronting consumers with security issues that in the past were issues only for big corporations, banks, the military and government agencies, said Steve Solomon, chief executive of Citadel Technology Inc., a security software company in Dallas whose products include Winshield and Folderbolt. "It's moving down into the small office and home office markets, to schools and to home computer users," he said. How does one keep confidential information private? And when the information is no longer needed, how does one make sure that it is completely erased? Both questions involve a combination of good computer security policies and good security software. The software is the easy part. Creating and sticking with good security habits is the hard part. "Technology exists today to protect individual privacy for as long as the individual chooses to keep the information private," said Scott Schnell, senior vice president of marketing at RSA Data Security of San Mateo, Calif. Computer users today have access to inexpensive software tools that can encrypt the contents of a file (including images), an e-mail message or even the entire contents of a computer so thoroughly that it can never be read by someone else in our lifetimes. Other programs can shred unwanted files so completely that no one can recover them. But very few people use such security tools. Computers are good at keeping secrets. Too good, in fact. The secrets can reside on a computer, and on a computer network, long after the user deletes them. The files are forgotten, but not gone. Deleting a file does not really delete the file. It merely hides it from view so it no longer shows up in a directory of files. It's like getting an unlisted telephone number. The listing may not appear in the phone directory, but the phone can still ring if someone knows the right number. When a user deletes a file, the computer stops listing it in the file directory and marks the disk space as available for reuse. Another file may eventually be written atop the same space, obliterating any traces of the original. But as hard disk capacities swell into the gigabytes, the space may not be overwritten for a long, long time. In that limbo period when the deleted file is undead, any moderately skilled computer user can locate, restore and read the deleted file by using such commands as "undelete" or "unerase," which are common features of many software utilities. The computer's ability to remember deleted files is most often a good thing, especially when important files have been deleted by accident. Every day, computer technicians get frantic calls from people who have inadvertently erased the boss's speech or the big presentation due the next morning, or who have children who have erased those boring Quicken folders to make room on the disk for games. At those moments, being able to resurrect the files from the dead seems like a miracle. There are a number of utility programs available that have an "unerase" capability, to be used both in emergencies and as a precaution against accidents. Examples include Norton Utilities from the Symantec Corporation. But as with most tools, "unerase" programs can be dangerous in the wrong hands. To truly erase a file and prevent it from being recovered, one must write over it, or wipe it. There are several utility programs available that enable the user to overwrite a single file or the entire disk, or anything in between. Such programs typically have apocalyptic names, such as Shredder, Flame File and Burn. Similar disk-wiping tools are often included in PC utility programs and encryption programs, but others are available for downloading without charge from the Internet. These programs typically hash over the designated disk space with meaningless patterns of ones and zeroes, instead of the meaningful patterns of ones and zeroes that represent the original information. That process renders the deleted file unreadable in most cases. The key phrase is "in most cases." Just as with encryption, there are people working just as hard to recover wiped files as there are people working to wipe them. Law-enforcement agencies and spies have developed ways to reverse a simple, one-pass wipe with ones and zeroes and retrieve the original file. So the Federal Government requires that sensitive files be wiped many times with random characters, which, in theory, obliterates the original file and makes it unrecoverable. Unless, of course, the file has already been copied onto backup tapes. In the digital world, the original file may be shredded, while one or more perfect copies can exist elsewhere. An even more bulletproof way to render files unreadable is to encrypt them. Encryption scrambles a disk or file, including pictures (or a telephone conversation, or a credit card sent over the Internet) so it can be opened and read only by the person holding the proper key, or password. The strength of the encryption is often measured by the length of the key, which is in turn measured in bits. In general, each additional bit of key length doubles the amount of effort needed for unauthorized users to break the key. Even weak encryption (with a 40-bit key length, for example) is sufficient to deter most casual snoops. Breaking a 56-bit key requires computing resources that are beyond the reach of all but the most determined code breakers, and even then it can require days of sustained attacks by a supercomputer just to crack one e-mail message. (The Government's National Security Agency, by far the most formidable group of code breakers on the planet, is thought to be able to break 56-bit keys in a much shorter time, said Enrique Salem, a chief technology officer at Symantec, whose products include Disk Lock, Norton Your Eyes Only, and Norton Secret Stuff. Some encryption programs available today use 128-bit keys, which are "infinitely unbreakable, at least in our lifetimes, even taking into consideration the predictable advances in computing power," said Schnell of RSA. In other words, it is more secure than the strongest physical vault ever built. Not even the National Security Agency is believed to have the ability to break a 128-bit key. And then there is e-mail. People type all sorts of embarrassing, confidential or intemperate words in e-mail in the mistaken belief that such messages are private. In reality, messages sent by e-mail are less secure than messages scribbled on a postcard. The way the Internet mail system works, an e-mail message passes through several exchange points, or nodes, on its way to the recipient's computer. The system administrator at each handoff point can in theory read the message, copy it, reroute it or tamper with it. If the message originates or terminates in a corporate computer system, chances are high that a copy will persist in the company's backup tapes or disk for days, at least. In the end, there are only two ways to keep information confidential in the digital age. One is to use strong encryption. The other is never to write it down or speak it in the first place. -o- Subscribe: mail majordomot_private with "subscribe isn". Today's ISN Sponsor: Repent Security Incorporated [www.repsec.com]
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