Is it possible to store ether on paper wallets or generate printable private keys offline somehow?

Cold storage has been discussed in the past on Ethereum's subreddit.

Just to give my 2 cents, on Ubuntu I use the following on the command line:

cat ~/.ethereum/keystore/<key_file> | qrencode -o qr_image.png

Add option -l H to get a code that is easier to decode. The qrencode tool uses the open source libqrencode library, and can be installed using:

sudo apt-get install qrencode

Once you have the image file, you can then print it off. (Using a wired connection to a printer, unless you're happy with the printer's levels of wireless security.)

A command line tool to decode a scanned QR code or image file is included in the zbar-tools package, e.g. zbarimg --quiet qr_image.png

The general disclaimer: You'll need to ensure you're happy with piping your keys into someone else's utility... The source code is available, but you'd need to be familiar enough with C to be able to check it isn't taking a copy of the key and then sending it back to the mothership.

  • 1
    It should be noted that for this to work you need to generate the keyfiles themselves using geth. – Tjaden Hess Jan 20 '16 at 23:26
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    And it works only with Ubuntu or mint. Maybe a bit too localized. Aren't there any paper wallet generators out there? – Afri Jan 23 '16 at 13:19
up vote 16 down vote accepted

MyEtherWallet.com

There is a paper wallet generator available at myetherwallet.com.

my ehter wallet

If you don't trust it, you can download it from github and run it offline.

EthAddress.org

There is another paper wallet generator available at ethaddress.org.

ethaddress

Source code on github.

Printing the private key for ethereum in geth.

This is done for creating a real *secure offline paperwallet in your own WM which afterwards stores the money independent from a program *.

Based on this posts and another post that points out that the source code of geth can easily be changed to print out the private key. Here it how it goes.

  1. Create a virtual machine with a linux. I took VirtualBox and an old Ubuntu minimal version (old because the minimal Installation without GUI is ease and fast done.)
  2. Building geth from source (i.e. Follow this tutorial github.com/ethereum/go-ethereum/wiki/Installation-Instructions-for-Ubuntu)

    -Note switch to a stable version of geth: git checkout

  3. Check if geth can be executed (and thereby update the latest nodes, not shure if this is required) type /build/bin/geth console --fast

  4. Shutdown the VM,
  5. Disable the network-Adapters in VirtualBox
  6. Restart the VM
  7. Modify the SourceCode as displayed in the pictures below. (The file to be modified can be seen on the headerline in the pictures.)
  8. Rebuild geth (make geth) as descipted in the Installation-Instructions in Step 2. Check if the Random-Number will be a good random value by executing cat /proc/sys/kernel/random/entropy_avail I have a Value above 3000 that is okay. (Google rng-utils to find how to increase the entrophy if below 200.)
  9. Create a new account via /build/bin/geth account new (the private key will be displayed after password was entered.).
  10. After created all accounts recheck if entrophy is still above 200 by execution the command from 8.
  11. cd ~/.ethereum/keystore/
  12. The private key and the public key is written in the filenames of the accounts in the keystore.
  13. Add 0x as prefix before the public key, because most programs expect it.
  14. To create the paperwallets from the filenames, easily the list of the keystores can be written to a file with ls ~/.ethereum/keystore/ >> paperwallet.txt and sent it to a printer. Note: The public key requires the prefix 0x to intend the usage as hex.
  15. Test some of the paperwallets **with small amounts of money. (Recive and Send Money)
  16. Note: The paperwallets are save until the day you used the private key for the first time for a transaction.
  17. If the tests succeed, and you have the wallets printed out, erase the VM.

Modify the Source-Code:

On the first picture: Make a Copy of the function keyFileName and name it keyFileNamePlusPK. Uncomment tx (this is important) and expand the fmt.Sprintf command.

enter image description here

On the second picture: Search the function storeNewKey and call keyFileNamePlusPK inside the method. Also add fmt.Println(„storeNewKey... Good Luck. !!!And Note i am not responsible for any problems comming from this post!!!

Additional option: Java based offline solution on GitHub.

Based on Richard's answer I created a bash script to build a more readable paper backup. As shown in the following example , the paper contains the address (to not confuse multiple keyfiles/papers) and the keyfile in both plain JSON and QR-code.

Such paper wallet is just a backup with same security as backed up keyfiles on a normal USB stick. In contrast to paper wallets produced by MyEtherWallet, the paper does not contain the unencrypted private key. I don't think anyone should ever print a private key on paper anyway.

example

#!/bin/bash

# Create paper wallet of ethereum keyfile
# requires qrencode, jq, and pdflatex

set -e

for keyfile in $@; do
    [ -f "$keyfile" ] || {
        echo "file not found: $keyfile" >&2
        exit 1
    }
    echo "$keyfile"
    dir=$(dirname "$keyfile")

    qrcode="$dir/$keyfile.png"
    latex="$dir/$keyfile.tex"

    # pretty-print JSON
    json=$(jq . "$keyfile")

    # address
    address=$(jq -r .address "$keyfile")

    # QR-code
    cat "$keyfile" | qrencode -l M -o "$qrcode"

    cat > "$latex" <<- TEX
\\documentclass{article}
\\usepackage{graphicx,listings,fullpage}
\\renewcommand{\\familydefault}{\\ttdefault}
\\begin{document}
\\section*{$address}
\\small\\noindent
\\includegraphics[width=0.5\\textwidth]{$qrcode}
\\begin{lstlisting}
$json
\\end{lstlisting}
\\end{document}
TEX

    pdflatex --quiet "$latex"

    # only keep the PDF
    rm "$qrcode" "$latex" "$dir/$keyfile.aux" "$dir/$keyfile.log"
done

Here's a new one with user customizable background artwork:

Memory Paper Wallet - Ethereum Customizable Paper Wallet https://bitcointalk.org/index.php?topic=3335760.0

enter image description here enter image description here enter image description here

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