Altough not so very common, it might be necessary to sign messages using only a paper wallet… Some people claim it’s impossible to do without compromising your key, and having to sweep your wallet.
However, i found a way to do it with minimal risk and exposure… Here’s how it works:
Preparation:
- Find your bip38 encrypted paper wallets, place them on your table
- Download the bitaddress sourcecode from https://github.com/pointbiz/bitaddress.org/archive/master.zip
- Download the latest working brainwallet.org sourcecode (this is not the head branch) from https://github.com/brainwallet/brainwallet.github.io/archive/f7679dd03f39a04edced641960a7c3df1116fea9.zip
- create a new textdocument using your favorite editor (gedit, notepad2, nodepad++, wordpad, nano, jed, vi,…), insert the message you want to sign in this textdocument and save
- Disconnect from the internet (even reboot afterwards, make sure you are disconnected!!!)
Procedure:
- While being disconnected, unzip the sourcecode of bitaddress.org and brainwallet.org
- While being disconnected, open the bitaddress.org.html of bitaddress.org using a browser that is relatively safe (a fresh chrome, opera, firefox installation will probably do)
- While being disconnected, in your browser, click on “wallet details”, manually copy the private key from your paper wallet in the “enter private key”-field, press “view details”
- While being disconnected, you will see a new input field emerging, enter your bip38 passphrase
- While being disconnected, open a new tab in which you open the index.html of brainwallet.org
- While being disconnected, at the top of this page, there is a “sign’-tab => click it
- While being disconnected, copy the Private Key WIF from the bitaddress.org tab to the brainwallet.org tab’s private key field
- While being disconnected, copy the message from your textdocument in the message-field, click “sign message”
- While being disconnected, copy the signed message to your textdocument and save
- close your browsers, close the text editor
- REBOOT
- reconnect to the internet… The saved message can be found in your text document 😉
