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I travel quite a bit and don't want to lug around a 2nd 'air-gapped' computer. I know that connecting a hardware wallet like a Ledger Nano S to the Ledger Live desktop app running on a computer that's connected to the internet not considered a 'fully cold' wallet setup.

I asked if a non-networked VM would do but it sounds like there's no extra security with that.

So, what would be a good solution for a 2nd 'air-gapped' computer for travelers? Perhaps Tails installed on a USB stick or 'OS on a stick' products that are out on the market, such as the Intel Compute Stick:

https://www.amazon.com/Intel-Compute-Computer-Processor-BOXSTK1AW32SC/dp/B01AZC4NHS
https://www.amazon.com/Intel-Corp-BOXSTCK1A8LFC-Compute-STCK1A8LFC/dp/B00W7KAABK

I'm looking for a solution where I can use my laptop's screen and keyboard.

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  • Unless you have a very unusual laptop, this is probably impossible: the only thing that can talk to your laptop's screen and keyboard is its own CPU. And so, for instance, if your regular OS gets some sort of malware that compromises your BIOS, then your "airgap" install gets compromised as soon as you boot it. – Nate Eldredge Jun 19 '19 at 18:39
  • Some hardware wallets don't need to be connected via USB, for example the 'Cold Card' can sign txs via SD card transfer. – chytrik Jun 19 '19 at 20:01
  • Chytrik, I looked at the Coldcard Wallet website but didn't see any mention of what desktop wallet app would accept a signed tx imported via the SD card. Also, could web wallets accept this signed tx? – ncruz Jun 21 '19 at 5:11
  • I just saw a link to a Medium post showing the use of Electrum on the desktop (Mac). Looks like the exported file is json. Do other wallets support this format? – ncruz Jun 21 '19 at 5:19
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This seems a lot like an XY problem. For the vast majority of users, the threat model simply does not require more guarantees than those provided by a solution such as Ledger.

Naturally, if you are dealing with very large amounts, you would be wise to take better steps to secure it. But something like a Ledger, which will parse the tx being signed and display the outputs on the Ledger itself prior to signing, should cover most use cases.

Additionally, as Chytrik mentioned, you have wallets such as the Cold Card which can operate without being directly connected to a computer at all, transferring Partially Signed Bitcoin Transactions via an SD Card.

Beyond that, if you really do need the security benefits offered by a fully offline computer, you should consider buying a cheap netbook or laptop, epoxy the ports, strip out any networking hardware, and verifying it as far as you can to be in a secure state - If you are genuinely moving amounts while travelling that merit that kind of security, then your best bet is to carry the extra 800 gram to 1 kilogram of weight.

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  • I will be storing large amounts and in multiple coins, so I'm looking for a fully offline solution that supports these coins. I have four laptops (2 Win, 2 Mac) and will be traveling with 2. Bringing a 3rd computer would be too much. I think a disconnected smartphone (networking disabled; no sim; no wifi/bluetooth) + micro SD card would be the solution. I'll even seriously consider 'stripping out any networking hardware' as you suggested. Can anyone suggest mobile app wallets that allow me to sign TXs and save the file to the SD card and on the flipside, load updates into it? – ncruz Jun 21 '19 at 4:46
  • Your use case sounds like you're at a point where consumer solutions simply won't exist, especially once you get into multiple coins - you should seriously consider hiring someone to build something like this for you. Most existing solutions you would find would be limited to Bitcoin, as it is one of the few coins designed with pure offline usage in mind - many altcoins make it rather difficult to handle things offline without an intricate knowledge of what you're doing. – Raghav Sood Jun 21 '19 at 5:54

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