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Comment by remcob | Hacker News Reader

Around when this was published I looked into the feasibility of pencil-and-paper wallets. What would it take to generate a key-pair using just pencil and paper?

There are tricks like big tables of precomputed multiples of the generator that make it easier, but you still need to do hundreds of 77 digit modular multiplications. And you want to be absolutely sure you made no mistake.

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It is theoretically possible, as there are just a few moving parts ( 2 tweets worth ): https://twitter.com/ribasushi/status/939954274569785344

Whether it is feasible... the amount of calculations around secp256k1 is likely practically prohibitive for pencil/paper.

Well secp256k1 private keys are just 32 random bytes (with some minor exceptions) so I think you could arrange something with a plain dice and a little bit of time.

Of course, but it would be cool if you could also calculate the public component on paper (and ideally verify it computerless as well). You could really create your bitcoin/ether/etc wallet with the public key only, whilst having an extremely low attack surface (private key never touches computer memory).

But remember the caveats about using the same key pair for multiple transactions: https://en.bitcoin.it/wiki/Address_reuse

I wonder if a slightly more feasible solution of producing and verifying a solution out of simple TTL, so there's no "computer" just a application specific machine made of simple commodity parts which one could trust reasonably easily would be actually worth something.

Generating the private key is the easy part; Just 77 rolls with a ten-sided die and re-try if it exceeds the prime. Or 256 coin flips, if you prefer binary.

It is computing the public key that is so hard.

For practical purposes I'd recommend an offline laptop, maybe running Tails OS and Electrum [0]. Public key is one thing and making transactions and signatures quite another.

[0]: https://tails.boum.org/doc/anonymous_internet/electrum/index...

A mechanical wallet would be awesome!

Now I want to read a steampunk sci-fi novel where cryptocurrency is mined on steam-powered devices. Of course, the algorithms should match the capabilities of the underlying hardware.

may as well create and sign the transaction on paper also.

For signing, both your private key and a random number k need to be kept secret. The process then involves scalar multiplication, modular inversion and two more multiplications — strictly more work than generating a key-pair.

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