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Specifically I'm looking for Armory-like functionality where the transaction can be generated on an online system, transported to an offline android tablet or netbook via USB or QR code where it can be signed, then transported back to an online system where it can be broadcast.
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Its not exactly what you want, http://mycelium.com/ for Android does it the other way around.
You keep your private keys safe in QR-code format on a paper or a offline device, then you scan it when you want to make a transaction. Mycelium signs the transaction and forgets about the key.
I tried to scan with my Android device offline, but it does not work. To be able to select previous outputs to send in the transaction, you need to be online.
I don't know of any Android app that can take a raw transaction (by QR-code, SD-card, OTG, Bluetooth, NFC or Chirp.io) and sign it offline.
I hope this feature will be implemented soon.
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The app "Bither" does exactly what you want (available for iPhone and Android). QR-codes are used for transfer (instead of USB stick in case of Armory).
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Yes Bither is exactly what you are searching for. From my point of view Bither is quite underestimated. Due to the cold storage functionality with a 2nd offline phone Bither seems to the be the safest wallet availabe for mobile phones (Android, iPhone). In addition it exists also for Windows.
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AS our friend said The app "Bither" does exactly what you want (available for iPhone and Android). it uses a method that is called air gaped cold storage; and I am describing it in a whole fashion.
for using Bither cold wallet you need two phones; one of which is your bither hot wallet the other is your bither cold wallet. the latter one keep your private keys and has the power of using them.
you may prepare a transaction QR code with your hot wallet (which is installed on a internet connected phone and can receive preferred wallet address of your partner, or you can make it by typing the transaction data by your own on the cold wallet's phone). then you should scan the QR code with your cold wallet's phone (not connected to the internet) and the cold wallet may sign the transaction and generate the special signature as a function of departure and destination wallets and the amount. the signature needs to be broadcasted to the bitcoin network; so the cold wallet generate a QR code which contains the signature of that special transaction. then it should be scanned by the hot wallet to be broadcasted to the network.
this method is called airgapped; because no USB stick or cable is in the middle. this method has the advantage that there is no risk left for malware or virus to be carried to the cold wallet. or there is no way for private keys to be leaked from cold wallet.
The Bither app also support HD Wallet which is the only type of wallet to be used for Bitcoin Core.
you can find more information on the bitcoin.org holy website. or read more about it on Bither's Github.
