Peter Gutmann is a computer scientist in the Department of Computer Science at the University of Auckland, Auckland, New Zealand; he also received his Ph.D. in computer science from the University of Auckland.
Interested in computer security issues, including security architecture, security usability (or more precisely the lack thereof), and hardware security, he has discovered assorted flaws in publicly released cryptosystems and protocols.
He is the developer of the cryptlib open source software security library and contributed to PGP version 2. He is also known for his analysis of data deletion on electronic memory media, magnetic and otherwise, and devised the Gutmann method for erasing data from a hard drive more or less securely.
The Gutmann method is an algorithm for securely erasing the contents of computer hard drives, such as files. Devised by Peter Gutmann and Colin Plumb, it does so by writing a series of 35 patterns over the erased region.
One standard way to recover data that has been overwritten on a hard drive is to capture the analog signal which is read by the drive head prior to being decoded. This analog signal will be close to an ideal digital signal, but the differences are what is important.
By calculating the ideal digital signal and then subtracting it from the actual analog signal it is possible to ignore that last information written, amplify the remaining signal and see what was written before.
In 1996, when this method was developed, it was possible to use a digital oscilloscope to recover eight levels of overwrites, without damaging the drive. Since then higher disk densities have probably reduced the number of overwrites necessary to completely erase data.
However, overwriting the disk repeatedly with random data will not always work. The permittivity of a medium changes with the frequency of the magnetic field.
This means that a lower frequency field will penetrate deeper into the magnetic material on the drive than a high frequency one. So a low frequency signal will still be detectable even after it has been overwritten hundreds of times by a high frequency signal.
The patterns used are designed to apply alternating magnetic fields of various frequencies and various phases to the drive surface and thereby approximate degaussing the material below the surface of the drive.