# Possession of this prime number is illegal in the United States, even if you write it on a piece of paper

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Primes donâ€™t kill people.
People kill people.

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The only thing that can stop a bad guy with an illegal prime number is a good guy with an illegal prime number. Waitâ€¦

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In the bank example/description of public/private keys, their description of how the primes are used is nonsensical. I think that heâ€™s trying to describe RSA encryption, but got it quite wrong.

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Good idea, but full of errors. For example"There are an infinite number of primes because there are an infinite number of numbers." Finding primes isnâ€™t hard, itâ€™s factoring their products that is hard. The primes used in RSA arenâ€™t of the form 3^n -1 or any such formula.

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I think he is trying to describe a mashup of Diffie Hellmann and RSA â€“ and yes, itâ€™s quite wrong and makes no sense even with the low-complexity primes he used.

Heâ€™s also glossing over a bunch of other things â€“ for instance how exactly the â€śillegalâ€ť prime corresponds to the source code he displayed, and also that everyone who copies DVDs is in possession of that prime (which is simply untrue). They are in the possession of something that prime represents in a particular manner (an algorithm expressed in machine-readable code), but no one was using that particular representation for decoding of DVDs.

The video also first tries to explain some kind of public key cryptography â€¦ and then â€¦ uh â€¦ well, then the reason the number is supposedly illegal has absolutely nothing to do with that public key cryptography. If he had explained how gzip works and how you can transform a primeâ€™s base-256 representation into an input for that, that might have been more useful.

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where is the full number? I need a copy for my wallet.

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Just google 09F9 and itâ€™ll guess what youâ€™re looking for. If youâ€™re looking for the DeCSS key, that is.

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I found it.

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Not even that. You can copy a DVD as an ISO image and never touch the content.

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I memorized it for convenience, and now I canâ€™t get it out of my head. Should I be worried?

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But then the song is from the 19th century, so itâ€™s probably not valid anymore in the much more enlightened 2010s.

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As long as you can restrain yourself from singing it in the shower, you should be fine.

Besides, itâ€™s not as if itâ€™s transcendental --a number that never endsâ€¦

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â€śAnd if I am thrown into the darkest dungeon,
all these are futile works,
because my thoughts tear all gates
and walls apart.â€ť

This is not as reassuring as you may have intended.

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Is that right? I thought transcendental numbers were infinite irrational numbers with the key feature that you canâ€™t construct one with a finite number of algebraic operations.

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I was an English major, so sue me!

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and this relates to the topic how?

ah, I see! youâ€™re preparing an insanity defence!

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If you knew as much about Egyptian history as the mathematics you stole that was invented by Kemetic Egyptians, you wouldnâ€™t be so glib!

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In middle school I wrote a term paper on ancient Egyptian mathematics, and IIRC the only fractions they had heiroglyphs for were unit fractions (1/x), so no transcendentals there

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