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LinuxSecurity.com: Linux Data Hiding and Recovery

Mar 13, 2002, 04:30 (0 Talkback[s])
(Other stories by Anton Chuvakin)

[ Thanks to LinuxSecurity Contributors for this link. ]

"It is common knowledge that what is deleted from the computer can sometimes be brought back. Recent analysis of security implications of "alternative datastreams" on Windows NT by Kurt Seifried has shown that Windows NTFS filesystem allows data hiding in "alternative datastreams" connected to files. These datastreams are not destroyed by many file wiping utilities that promise irrecoverable removal of information. Wiping the file means 'securely' deleting it from disk (unlike the usual removal of file entries from directories), so that file restoration becomes extremely expensive or impossible.

"Some overview of what remains on disk after file deletion, how it can be discovered and how such discovery can be prevented are provided in Secure Deletion of Data from Magnetic and Solid-State Memory by Peter Gutmann. The author recommends overwriting files multiple times with special patterns. Against casual adversaries, simply overwriting the file with zeros once will help.

"Linux has no alternative data streams, but files removed using /bin/rm still remain on the disk. Most Linux systems uses the ext2 filesystem (or its journaling version, ext3 by Red Hat). A casual look at the design of the ext2 filesystem shows several places where data can be hidden..."

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