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[kingcolex]

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[Malin Keshar]

Its hard to warranty the phones will never connect to the internet, and 100% sure they communicate with your phone service provider via their cellphone network. With a notebook you at least can remove the wireless and bluetooth cards.

For me a cheap notebook and pendrives are more recommended.

[gtraah]

Its hard to warranty the phones will never connect to the internet, and 100% sure they communicate with your phone service provider via their cellphone network. With a notebook you at least can remove the wireless and bluetooth cards.

For me a cheap notebook and pendrives are more recommended.

Gsm with no Sim? put into airplane mode ASAP?

Yep this is what I was thinking, More portal, more cheaper, and you can use Mycellium ... In my view this is how a wallet should work..

I have a Cold Storage which is TOTALLY offline, BUT I have it in view mode only in my mycellium app, meaning I can send to it and I can view all transactions incoming outgoing but the private key does not exist on the phone.

Lets Say one day I want to make a transaction from it and then leave the rest exactly where I left it? Simple, I open my safe, take out my paper wallet scan the private key send the amount I want and delete the key after its sent soon as I hit the delete button its gone straight back offline

[Ron~Popeil]

Sounds like a pretty secure idea and much less expensive than buying a computer to do nothing but store bit coin. Will one of these work without a sim card installed? 

[AliceWonder]

What is the advantage over a deterministic paper wallet?

My understanding is you can make a deterministic paper wallet with Armory where you can continue to create fresh addresses to send to w/o needing the private key in your client.

[ranochigo]

If you have to send them, you would still have to connect to the internet. You will eventually connect the micro SD to a online computer one day and the data can be stolen. The microsd may have weak lifespan and gets damaged fast, there is always a risk about hardware dying.

[shorena]

Sounds like a pretty secure idea and much less expensive than buying a computer to do nothing but store bit coin. Will one of these work without a sim card installed?  

Yes there are even "smartphones" out there that have no sim slot in the first place. My problem is that I cant remove the WiFi chip though, might be my tin foil hat speaking.

Old phones should also be easy to get for free, just ask around.

If you have to send them, you would still have to connect to the internet. You will eventually connect the micro SD to a online computer one day and the data can be stolen. The microsd may have weak lifespan and gets damaged fast, there is always a risk about hardware dying.

Data can be transfered via QR code. IIRC Bither uses that system to transfer data between hot and cold version.

[river333]

Why not use a Raspberry Pi or similar? Cheap, small, and you don't have to worry about wifi.

[shorena]

Why not use a Raspberry Pi or similar? Cheap, small, and you don't have to worry about wifi.

Well there are a couple downsides to the pi, they are more expensive, you're probably going to have to order one, they need an sd card (which they eat), they need a bit of knowledge (I am talking about easy cold storage for everyone) , they need a tv or monitor.

I think the wifi is not an issue but that is me personally, if it is disabled and stays in a signal blocker bag i don't see how it could compromise security. (Totally open to reasons why)

I like the idea with the bag. Any faraday cage would work, e.g. the right box. I will see if I can get an old phone and test that. I wanted to setup and old laptop, but this would be way easier. At least I think so.

[ronimacarroni]

If you just want to store the key then just get a cheap pda off of ebay for like a dollar.

[Brooker]

Doesn't sound like a bad idea, but you would still need to connect it to the internet to make transactions. Android phones can also get viruses I believe so watch out for them. I'd just use a linux live cd instead of this, though.

[zeetubes]

I think it's a great idea but I would like to hear from people who disagree. I bought an ultra cheap android phone in china - $27 (ok I bought two so I can build a duplicate and send it to my brother as backup). No sim, powered up, reset to factory default, then removed apps that I didn't think I would need, games and messaging etc. Disabled wifi and BT, set up a pin to lock the phone.

I used my main everyday phone to backup the apps I wanted onto an SD card, probably just mycelium would be sufficient. Transferred the SD to the cheap phone, installed Mycelium and set up the pin to protect Mycelium. Write down the 15 character Mycelium passphrase. Then make a few test transfers and eventually send a few bigger sums (I haven't done this yet). Power off the phone, take the sd and move it to the backup phone. Go through the same process but restore the key from the first Mycelium wallet (I haven't done this step yet either). I'm probably going to use separate physical mail to send the pins and passphrase to my brother and ship the backup phone separately. But I'm still missing a few steps before I totally commit. I've had the phones for a few months and they power up ok so no issues with reliability yet. If it sounds like a good plan it would be great to build a step by step tutorial.

[Meuh6879]

on a phone, you can't roll back ... so install a bitcoin client is useless to cold storage.
because, when you connect to internet (to spend bitcoin) ... your client don't want to connect to others clients.
you update the client (after 2 years example) ... and you LOST the cold storage file.

i already have this.

i use, now, ONLY to cold storage ... the official bitcoin core.

[Meuh6879]

because backup file (from 2 years) don't work with the new client updated in the phone (since 1 hour) + private key are encoded ... (BIP something like that)

[counter]

I've got one of these that I never use and I've wondered if it was a safe option.  I think I'll give this a try because I don't use it since I've got my pc.  Is it an issue if you have used it online before, does it matter if I have used it online not in airplane mode  in the past?  Does that somehow affect the integrity of the security?

[ranochigo]

because backup file (from 2 years) don't work with the new client updated in the phone (since 1 hour) + private key are encoded ... (BIP something like that)

You can extract the private key and create and sign a raw transaction then broadcast it. The format would most likely still be accepted by the community. It is a good idea to stay in touch within the bitcoin community for updates.

[ranochigo]

I've got one of these that I never use and I've wondered if it was a safe option.  I think I'll give this a try because I don't use it since I've got my pc.  Is it an issue if you have used it online before, does it matter if I have used it online not in airplane mode  in the past?  Does that somehow affect the integrity of the security?

The only thing would be a risk is custom Roms. Some of them have backdoors but they cannot send data without internet so it can still be used as a cold storage. Always remove your SIM card first. Factory reset first then get the wallet then copy to somewhere safe and if you need to use it, factory reset it again.

[beetcoin]

smartphone sounds like a smarter plan to me than a laptop.. it's much smaller and easier to conceal.

[sed]

I agree that it sounds like an ok plan, but I don't really see the advantage over just generating a keypair and keeping it safe on a piece of paper or whatever.  If you don't plan on sending the bitcoins anyway, you can see any coins you send to it by just looking at a public block explorer.

[Candystripes]

Great idea actually, although you could always just put it onto a USB and put it somewhere safe in your house.