I’m happy to publish a draft of my innovative scheme that enables blind signatures compatible with Bitcoin transactions. Primary motivation is secure storage for bitcoins. You can lock your funds with multiple friends/custodians (in a M-of-N multisignature transaction) and ask them to unlock your funds later. If done naïvely, custodians will be able to see which transaction they signed and how much money you have. Blind signatures allow you to completely hide your transactions from custodians who sign them. The scheme differs from existing blind signature proposals in two important aspects: 1) it is compatible with ECDSA while others are not and 2) it completely unlinks resulting signature and public keys from the signing parties, providing absolute privacy.

Paper describes motivation, core protocol and provides a practical way to generate and keep track of all secret and public parameters used in it. Use of this scheme enables the ultimate solution to secure Bitcoin storage. While your personal hardware and software wallets can be compromised, money can be much safer locked with independent semi-trusted parties, yet absolutely privately. You and your friends can use conventional personal computers to lock your personal pension funds among each other without ever exposing sensitive financial information.

Download the paper here: http://oleganza.com/blind-ecdsa-draft-v2.pdf

Demo app: https://github.com/oleganza/blindsignaturedemo

I timestamped SHA256 of the second draft on June, 16 2014. Used SHA256 of the PDF as a private key and sent 0.0002 BTC to corresponding address 1FM9JtztQKwUVshxVJnEv8JEGKPZkCu7qk.

SHA256: 85e0a79b80f75f88790135214564847d2de46062414f08e799e5f701fddbfddc

Tx ID: https://blockchain.info/tx/ee0c7527de579d7ab2732be49a8b57fe13af940caff2c429464cd659e23281a6

Address: https://blockchain.info/address/1FM9JtztQKwUVshxVJnEv8JEGKPZkCu7qk

To verify:

1) Compute SHA256: $ openssl dgst -sha256 blind-ecdsa-draft-v2.pdf

2) Paste it as a “secret exponent” on brainwallet.org and get the address.

3) Find the earliest transaction on the blockchain for this address.