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Author Topic: Secure Offline 2 of 4 Paper Wallet  (Read 974 times)
DBordello
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March 23, 2013, 11:51:37 PM
 #1

Is there a secure way to generate offline a paper wallet that requires 2 of 4 to redeem? 

Additionally, is there any software that redeem n-of-m wallets?

I have seen some good paper wallet generation scripts, but not any n-of-m.

Any insight is appreciated.
Dan

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Michael_S
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April 26, 2013, 01:58:42 AM
 #2

I can only know of Shamir's Secret Sharing Scheme (install ssss on Linux, then uses the commands "ssss-split" and "ssss-combine"), but you probably know this already.

It is adequate for encrypting arbitrary strings (of limited length) in an "n out of m" fashion..., e.g. n=2, m=4.

Such a string could either be a private key, e.g. in WIF 51 base58 format,
or a password of a zip or truecrypt file that contains a complete wallet.

The 4 outputs strings of "ssss-split" can then be printed as a sort of paper wallets.

One could certainly write a bash script that makes use of "ssss" but has a more user-friendly and bitcoin-specific interface, e.g. that queries the user for entering the private key, the values for n and m, and where to write the outputs to - e.g. to m different txt files of a certain naming scheme.

Such a script could also call "vanitygen" - then you would have a suite that does it all: Generate a private key (with vanitygen), then splits this key into m (e.g. m=4) strings of which n (e.g. n=2) are needed to reconstruct the key, and write them to m different txt files.

PS: If it does not exist yet, I can certainly write such a user-friendly Linux bash script for a bounty.

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April 26, 2013, 02:00:35 AM
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P2SH multisig will do it.

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April 26, 2013, 02:13:07 AM
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I created a command-line tool for splitting your Armory wallet into M-of-N pieces, for backup purposes, only.  You can find the description and instructions here:

https://bitcointalk.org/index.php?topic=149820.0

I am in the process of integrating it into the GUI so that M-of-N (using Shamir's Secret Sharing) will be a default backup option. 

However, this is only intended for backup.  If you want to split the signature-scheme across multiple computers (i.e. to use it for every new transaction), you want multi-sig.  Unfortunately, no clients support multi-sig yet Sad  Armory will, hopefully in the near future.  Until then, I am hoping to get this "fragmented backup" thing integrated so people can at least backup their single-sig wallet securely (i.e. 2-of-4, put one piece in safe-deposit box, put one in your home, give one to each of two trusted friends without telling them anyone else has any pieces).  If your offline computer dies, go fetch.

Founder and CEO of Armory Technologies, Inc.
Armory Bitcoin Wallet: Bringing cold storage to the average user!
Only use Armory software signed by the Armory Offline Signing Key (0x98832223)

Please donate to the Armory project by clicking here!    (or donate directly via 1QBDLYTDFHHZAABYSKGKPWKLSXZWCCJQBX -- yes, it's a real address!)
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