Ride the Lightning

OF MD5 COLLISIONS AND TRAIN WHISTLES

October 10, 2008

Why train whistles? Today we had two “firsts” on the lecture circuit.

We were in Winchester, Virginia – a charming place, home to the annual Apple Blossom Festival, and a warm, wonderful audience. This was the first time we have ever given a CLE presentation in a “brew pub.” Super idea, except that there was nary a sip of suds to quench the thirst of the presenters. Sad to say, the bar was scheduled to open for the afternoon session. We had the singular disadvantage of being booked for the morning session. Timing is everything.

Greatly to our amusement, we were right beside the train tracks. As a result, we were intermittently forced to shout over the blast of the train whistles. As you can see, the lecture circuit is a series of novel adventures. . .

And on to MD5 collisions – in a previous post, I mentioned that all MD5 collisions which have thus far been documented have been “forced” and have not occurred in the wild. A reader wrote with a follow up question – and I must apologize because I seem to have “misfiled” (never say lost) his e-mail, so I cannot tip my hat and thank him by name.

To answer his question, the likelihood of two naturally occurring differing files having identical MD5 hash values has been calculated by experts to be 340 billion, billion, billion, billion. In short, you are not likely to ever see it. Just for grins, the exact number is 340,282,366,920,938,463,463,374,607,431,768,211,456.

You could be struck by lightning and win the lottery many times over before you would see this in real life.

To my reader who asked, I dimly recall a second question being in your note. If you should see this post, please ask the second question again and I, for my part, will try not to “misfile” it a second time.

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