Open-Sourcing Subzero: Square’s Bitcoin Cold Storage Solution

Re:Open-Sourcing Subzero: Square’s Bitcoin Cold Storage Solu... by haneefmubarak on Monday October 22, 2018 @11:01PM (#18280423)

This is neat, but I think it'd be interesting to see a writeup that talked more about why they needed a new solution and what they did differently that solved their particular problem.

In particular, they mention an onion model - what does that look like for them? Hot/warm/cold can take a variety of forms...

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Re:Open-Sourcing Subzero: Square’s Bitcoin Cold Storage Solu... by amenghra on Monday October 22, 2018 @11:23PM (#18280499)

The main motivation to build vs use an existing solution was a solid backup/DR story and the desire to be able to write custom business logic which is enforced inside the HSM.

It’s things like controlling where funds can go, or requiring specific authorization based on amount being move around, etc.

Being able to leverage hardware we are already familiar with or which has various certifications (such as Fips) is a neat bonus.

If you look at the code, you’ll see that the funds flow from “anywhere -> hot -> cold -> warm -> anywhere”. This is the minimal setup and you can add more layers if needed.

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Re:Open-Sourcing Subzero: Square’s Bitcoin Cold Storage Solu... by tudorconstantin on Tuesday October 23, 2018 @01:07AM (#18280852)

With HD wallets you can generate receiving addresses based on the master public key of a wallet, without needing any private key.

Is there a reason for not receiving funds straight into the cold wallet?

Edit: in the docs it seems that you indeed receive funds directly in the cold wallet

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Re:Open-Sourcing Subzero: Square’s Bitcoin Cold Storage Solu... by amenghra on Tuesday October 23, 2018 @01:51AM (#18281017)

You are right. You can go from external entity to cold wallet directly. The important piece is how the funds leave the cold wallet.

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