offline bitcoin wallet which only creates transaction-QR-codes

[Lumpi101]

Hello,

I'm new here and this is my first contribution here.
I think about buying some (or one) bitcoins but until now i have never done anything with bitcoins yet. So please forgive me if I make a false assumption, error in reasoning or something like that =)

I would like to have a bitcoin wallet which lies on a (perhaps old one but especially for that reason) smartphone. This smartphone shall, for security reasons, never be online. So in order to make transactions I have to create a transaction order (I'm sure there's a better word for that but... I don't know it...) with the offline phone and transfer this order (ideally with a QR code) to some online device that forwards this order to the bitcoin network.

Is there a bitcoin wallet (android?) that can create such transaction order QR codes? And is there a program (android/windows?) that can read and forward these transaction orders? Additionally, it would be very nice if the offline wallet provides encryption so that the private key is encrypted by a passphrase.

I really would like to do it that way because I don't want to entrust my bitcoins to some online hoster. I want to store my bitcoins by myself SECURELY.

(I know there are some hardware wallets... that would be plan B =))

Thanks for your help!
Lumpi

[Shendelzare_Silkwood-]

i found these :

http://www.newsbtc.com/2015/07/01/offcoin-making-offline-bitcoin-transactions-possible/

https://www.mobilpay.ro/public/en

 never try it before , it seems that wallet can make an offline transaction

" Netopia has noted that this system already works for Android OS version 4.1 or higher that accept microSD cards. “We have an USB version available for testing and soon one that is compatible with iPhone. This was designed to be universally acceptable and not a solution for high end phones,” said Eram. “Our vision is to enable offline bitcoin transactions anywhere in the world, including the areas where phones are not exactly high end.”

[achow101]

There is no such thing as a transaction order. There are payment requests, but they basically mean nothing.

What you want is called a watch-only wallet. This watch only wallet only has public keys, no private keys. The private keys are kept offline in your offline wallet. How watch-only wallets work is that they have the public keys of your wallet and can thus give you addresses when you want them. You give these addresses to people so that they can send Bitcoin to you. The watch-only wallet watches the network for any transactions that pertain to any of your addresses and it stores that information. When you go to create a transaction in order to send, the watch-only wallet builds the unsigned transaction and some extra information. Then you take that to your offline machine so that it can sign the transaction with the private keys. Then the signed transaction is taken back to the watch-only wallet and broadcast to the network.

There are multiple software which can do this. Some of them require that you generate a set number of addresses on the offline machine and use them on the watch-only wallet, and then once those addresses are used, you have to go back to the offline machine to generate more. Others use non-hardened BIP 32 deterministic keys so once you get the master public key on your online machine you never have to go back to the offline machine to get more addresses.

I recommend that you use Electrum for this. You can set up the offline wallet, get the master public key, and import that into an online electrum wallet (note online does not mean web) so that that is a watch-only wallet.

[devans]

Welcome to the forum, Lumpi.

Unfortunately what you're looking for exactly is not possible because access to the blockchain is needed to build the transaction. However, the next best thing is nearly as good: You can keep a watch-only version of your wallet on a device connected to the internet while keeping your private keys on an offline device. This is how it works in practice:

1. Build the transaction with the watch-only wallet.
2. Somehow copy the unsigned transaction to your offline device.
3. Sign the transaction on the offline device.
4. Somehow copy the signed transaction to your watch-only wallet, which broadcasts it.

Electrum is a desktop wallet that supports this. I'm not aware of any Android wallets that do the same, but perhaps someone else has some suggestions in that regard.

[Lumpi101]

Thanks for the hints and explanation.

Obviously, I want a watch-only wallet

bitcoin.org says, there is also an Android version of Electrum. I'll take a look at it!

[Lauda]

Are android wallets more or less safe than desktop wallets? It would see that desktop would be more secure but I dont know. Please help.

Smartphones are generally a unsafe environment (both privacy and security wise), thus android wallets are generally also less safer than their desktop equivalents. I do not know what the status is on wallet malware for smartphones though.

[RealBitcoin]

I would like to have a bitcoin wallet which lies on a (perhaps old one but especially for that reason) smartphone. This smartphone shall, for security reasons, never be online. So in order to make transactions I have to create a transaction order (I'm sure there's a better word for that but... I don't know it...) with the offline phone and transfer this order (ideally with a QR code) to some online device that forwards this order to the bitcoin network.

The phone is always online, it connects to cell towers. So a phone malware can send out private keys to cell towers through sms to hacker.


No better just use a hardware wallet or an offline PC, or something like that.

You can install electrum, you can send transaction through QR code from offline to online. You can use the smartphone to read the QR code, while the electrum will generate it.

That is a much better strategy.