# Crime novel trope: special passphrase deletes all data

**URL:** <https://boards.straightdope.com/t/crime-novel-trope-special-passphrase-deletes-all-data/924690>\
**Category:** Factual Questions\
**Created:** [November 4, 2020, 12:49am UTC](https://boards.straightdope.com/t/crime-novel-trope-special-passphrase-deletes-all-data/924690 "2020-11-04T00:49:42Z")\
**Posts on this page:** 1\
**Page:** 3

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**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\
**Post date:** [November 6, 2020, 3:53am UTC](https://boards.straightdope.com/t/crime-novel-trope-special-passphrase-deletes-all-data/924690/41 "2020-11-06T03:53:02Z")

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> [@DPRK](#):
>
> Not what I meant. Let _K_ be the important secret key. Choose 19 random numbers _K1, …, Kn_ of the **same length** as _K_ , and just pick _K20_ = _K_ ⊕ _K1_ ⊕ _K2_ ⊕ … ⊕ _K19_ .

And a similar technique:  
Pick a random polynomial f of degree m. The key is the value f(0). Then, generate n partial keys Kx=f(x) with n\>m and x random. Throw away the polynomial and the real key. To reconstruct the polynomial and solve for the key, only m+1 partial keys are needed, but you can generate as many as you want. If you’re slightly forgetful, you can set m=17 and n=20 for example. That gives yourself a bit of wiggle-room without compromising the security of the remaining partial keys. IIRC you want to do the whole thing in some alternate arithmetic, say Galois arithmetic, but the same principle applies.

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