I should probably explain a little what this "proof of existence" actually is and what it can be used for.
The printout you see in the photo is neither necessary nor adequate to proove anything, it's merely a printout of some data to make it easier to verify/find the data.
The actual proof that the coin existed at a certain point in time (in this case May 31st 2013) is in the Bitcoin Blockchain.
Here's what I did to produce this proof
- Scanned the front and back of the coin and made one image from those 2 images
- Took sha256 of that image (a tif)
- Used that checksum as a bitcoin private key to produce a bitcoin address
- Sent BTC 0.0001337 to that address
Here's how the existence of the coin on May 31st can be proven:
- Take the .tif image of the coin and compare it to the coin itself to verify the coin at hand is the coin in the photo (this can be done very reliably by looking at little scratches and orientation of the firstbits and sticker)
- Take the sha256 of the tif
- Convert it to a Bitcoin Address (using for example bitaddress.org site or the method explained here. You can also import the private keys into a wallet and then take the addresses from the wallet.
- Search for a transaction to that address in the blockchain (you will in this case find this transaction I used for the first 25 coins
Here's why such a proof can be useful in the future:
Currently it's highly likely there are no counterfeits of casascius coins around. It's just not worth the effort yet.
However assume it's the year 2023 and you decide to sell your precious 0.5 BTC coins back from 2013 when the first batch of these was made and the potential buyer is sceptical because there are now counterfeits around. Wouldn't it be great if you could proove that this coin has actually existed back in May 2013? It probably would increase the buyers confidence quite a bit. Well: you can.
Here's Mike himself suggesting resellers could do this:
Cryptography is one of those things that gives me a leg up on every possible counterfeited item in the world.
I assume my product WILL be counterfeited. But when I start producing digitally signed PDF photos of my own product, I've got the counterfeiters beat. The more possible I can make it for you guys to authenticate my genuine products, the more value a genuine product will have, and the less lucrative it will be to counterfeit them.
This will only work for products I produce from today forward, but here is an idea you can do right now. The counterfeiting hasn't happened yet. Go throw your current stash of Casascius Coins on a scanner, scan a photo of them, take a 160-bit hash of the file, and then work that hash into the block chain somehow. Convert the hash to a bitcoin address and send a satoshi to it (my Bitcoin Address Utility can do this, for example). Your photo with its supporting hash in the block chain will be publicly verifiable proof that the coin in your photo existed today.
I assume my product WILL be counterfeited. But when I start producing digitally signed PDF photos of my own product, I've got the counterfeiters beat. The more possible I can make it for you guys to authenticate my genuine products, the more value a genuine product will have, and the less lucrative it will be to counterfeit them.
This will only work for products I produce from today forward, but here is an idea you can do right now. The counterfeiting hasn't happened yet. Go throw your current stash of Casascius Coins on a scanner, scan a photo of them, take a 160-bit hash of the file, and then work that hash into the block chain somehow. Convert the hash to a bitcoin address and send a satoshi to it (my Bitcoin Address Utility can do this, for example). Your photo with its supporting hash in the block chain will be publicly verifiable proof that the coin in your photo existed today.