Another day, another Grin bounty

Development and Technical Discussion
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Today I got tempted to offer a modest $100/$200 Grin spam resistance bounty in the bitcointalk OP_RETURN debate [1]. Here’s hoping I didn’t screw up the conditions, and it actually holds up…

[1] Removing OP_return limits seems like a huge mistake

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I wish I was smart enough to participate, however I’d have no clue where to start. You’re a wizard of math and Grin is lucky to have you around.

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The bounty asked for

any scheme to store (10KB + X) of arbitrary data on a pure Mimblewimble chain using at most 100KB of total transaction size + X extraction data size, with extraction running fast and not revealing keys that allow the pruning of stored data. This corresponds to a >= 10% storage utilization rate.

It’s possible to achieve a rate of 1/3 [1], but whether extraction runs fast is up for debate. It requires computing the i’th 32-byte chunk of arbitrary data as private key

x = (s - i) * Hash(R|P|m)^-1

for each signature (s,R) with public key P, public nonce R, and kernel features m, where R is recognized as corresponding to a very small nonce i.

[1] Utreexo - advantages, state of development etc ...

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