Ride the Lightning

DO IDENTICAL FILES EVER HAVE DIFFERENT HASH VALUES? AH . . . NO

September 29, 2008

Before I get to the title question above, I have to tell you that we are in W.V., where (could I make this up?) the front page of The Dominion Post has a headline reading “Charge dropped against man accused of farting.” For those of you wondering how such a charge could come about . . . we had heard the previous day that a presumably inebriated man had lifted his leg in the police station, and well, the headline says it all – and then he fanned his emission toward the police officer attempting to administer a breathalyzer test. As a result, he was charged with battery. Silly, but we can understand that the officer was unhappy.

Normally, the paper slipped under our hotel door doesn’t cause us to howl, but that was pretty darn good. We also had the opportunity, thanks to our gracious hosts at the WVU Law School, to watch the Mountaineers lay waste to the Marshall football team. Not being a football fan myself, I watched the 3 day hoopla surrounding the game with amazement – the Roman Circus had nothing on this.

And back to the real subject – electronic evidence – which was the focus of the WVU Law School’s conference. Apparently, one of our faculty colleagues at the conference had warned the audience that two identical files could produce two different MD5 hashes if located on different hard drives, scanned from different computers. John and I suspect that this misinformation came from an error in a widely recently viewed webinar. We gently corrected the audience the following day, and it seemed worthwhile to ensure that any readers of this blog have not suffered a similar misapprehension. Two identical files, no matter what media they are located on or what computer they are scanned from, will always produce identical MD5 hashes. Precisely because this is true, its authenticity is maintained as it is transferred to different media.

OK, it’s not a sexy point. But it is imperative to understand. Onward to Grundy, VA and the Appalachian School of Law. No doubt about our accommodations – the only game in town is the Comfort Inn and we understand that the major decision point is which fast food or pizza joint to eat in. There goes the diet.

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