Audible free book: http://www.audible.com/computerphile
Hashing Algorithms are used to ensure file authenticity, but how secure are they and why do they keep changing? Tom Scott hashes it out.

More from Tom Scott:    / enyay   and   / tomscott  

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This video was filmed and edited by Sean Riley.

Pigeon Sound Effects courtesy of http://www.freesfx.co.uk/

Computerphile is a sister project to Brady Haran's Numberphile. See the full list of Brady's video projects at: http://bit.ly/bradychannels