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r/Bitcoin: using a Coldcard Q with a self-rolled dice seed as a pure signing device

reddit-coldcard-q-self-rolled-signing

https://www.reddit.com/r/Bitcoin/comments/1vkgatv/coldcard_q_security_with_selfrolled_seed_as_pure/

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  1. Earliest copy held Current
    seen · Captured here 7,794 chars
    Extracted text as captured 
    post: 1vkgatv
author: proper_turtle
created_utc: 1786355158
title: ColdCard Q Security with self-rolled seed as pure signing device
body:
Hi everyone,

so after the Coldcard dilemma I self-rolled my seed using dice (and only picked the 24th word using the suggestion from Coldcard Q when entering the 23 other words) because I also don't trust the new Coldcard Firmware from those scumbags.

So I'm still on the old firmware. I know the RNG and some connected functionality (like Paperwallet) is vulnerable, but I only want to use it as a signing device for my self-rolled seed (with passphrase, btw).

The only way the seed would be vulnerable (imo) is if the Coldcard's QR Export to Sparrow Wallet (which I'm using) would somehow export the private key as well, which is probably highly unlikely since Sparrow Wallet is not controlled by Coinkite (and I'm not even sure if Sparrow Wallet supports getting the private key that way).

What do you think, is the Coldcard Q secure as a pure signing device? I might take a look into the Coldcard Firmware Codebase again, but the last time I did (just quickly) I couldn't find the function for the Sparrow Wallet export.

Unfortunately the other HW Wallet I had (bitbox) died some time ago, and also I really like the keypad on the Coldcard. It's unfortunate there are (almost?) no other Wallets which have a keypad like that.

comment: p2t1jj1
parent: t3_1vkgatv
author: JumpProfessional3372
created_utc: 1786356077
edited: false
body:
Lot of the people who followed CC's paranoid guide are on the same boat, kept using coldcard as always, no need to update unless we learn that old firmwares can leak a private key or stuff like that.

Obviously these issues, if hey happen, while they are critical, they are less risky than the RNG bug.

Here I'm running 5.2.2 on the MK4.

comment: p2t1pcb
parent: t3_1vkgatv
author: Realistic_Junket4452
created_utc: 1786356155
edited: false
body:
the qr export is just a psbt, sparrow never sees your private key. that's the whole point of air gapped signing

  
the dice seed + old fw is about as safe as it gets tbh. the rng thing only matters if you're generating on the device which you're not doing

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