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Nine Algorithms That Changed the Future by Chris Bishop, John MacCormick

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9

Digital Signatures: Who Really Wrote This Software?

To show you how mistaken you are, and what an unfounded assumption yours is, I will lay before you a certificate…look at it! You may take it in your hand; it's no forgery.

—CHARLES DICKENS, A Tale of Two Cities

Of all the ideas we'll encounter in this book, the concept of a “digital signature” is perhaps the most paradoxical. The word “digital,” interpreted literally, means “consisting of a string of digits.” So, by definition, anything that is digital can be copied: to do so, just copy the digits one at a time. If you can read it, you can copy it! On the other hand, the whole point of a “signature” is that it can be read, but can't be copied (that is, forged) by anyone other than its author. ...

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