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These physical coins are supposed to be worth 1 BTC each - they have a hologram and a private key that somehow gives access to a real (digital) Bitcoin.
What is the process of claiming this real (digital) BTC for the physical one?
How can one redeem a Casascius Physical Bitcoin?
Answers
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The first 8 characters of the public address are on each coin, which allows you to obtain the full address or check the balance at FirstBits or a similar service. Beneath the tamper-evident holographic sticker on each coin is the private address which corresponds to the public address. Once you've obtained both the public and private address, the process for importing this information into an existing wallet has already been documented in this prior question.
Edit: On a side note, it's probably worth noting that this process is almost identical to the process used to redeem BitBills
Edit 2: Apparently these coins use a different private key format than standard. Casascius has published a utility to convert these private keys to standard addresses and more about the "mini private key" format can be found at the wiki. For those lacking a copy of Visual Studio, I've compiled a copy for your convenience. These keys may also be computed using any calculator or code capable of generating an SHA256 hash:
SHA256("S4b3N3oGqDqR5jNuxEvDwf") = 0C28FCA386C7A227600B2FE50B7CAE11EC86D3BF1FBE471BE89827E19D72AA1D
Of course that's still in hex and needs to be converted to Bitcoin's modified Base58 but many wallet import tools will accept hex as well.
Edit 3: Just heard from Casascius that we may be able to redeem these coins, as well as any device bearing a mini private key directly at MtGox in the near future.
Edit 4: Support has officially been added
1Can't wait to see what happens in Edit 5. Also, this first season is going to be hard to top--will season two stick with all the same characters, or try to switch things up a little with some fresh faces? – eMansipater – 2011-10-07T17:12:55.273
LOL well I usually try not to make so many edits, but the answer to this one keeps changing :) – David Perry – 2011-10-07T17:18:34.610
Gox is dead. You should probably edit those parts out. – 4276 – 2015-01-13T02:23:47.783
These coins use the Mini private key format. Are you sure the import method is the same? – nmat – 2011-09-07T04:05:21.173
Hmmm, you may be right about that one. More research is merited. I'll see what I can turn up. – David Perry – 2011-09-07T04:22:23.423
2Answer should be somewhat more complete now. – David Perry – 2011-09-07T21:05:28.010
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I just want to add a few things about the Mini private key format.
This is essentially a compressed way to store a bitcoin private key. Casascius coins small, so the private key is represented by 22 characters printed like this:
S4b3N
3oGqDq
R5jNux
EvDwf
To get the real private key, you just have to calculate the SHA-256 hash of the string. There are many online tools to calculate hashes and most linux distributions can quickly do it from the terminal:
$ echo -n "S4b3N3oGqDqR5jNuxEvDwf" | sha256sum
0c28fca386c7a227600b2fe50b7cae11ec86d3bf1fbe471be89827e19d72aa1d
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It is now possible to redeem a Casascius private key at MtGox if you have an account there.
Under "Add funds", choose "Redeem private key", then "SHA-256 Private Key". The full amount of the private key will be added to your MtGox account.
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http://StrongCoin.com provides the ability to create an account from an imported MiniKey. They have a fee of 1% of each spend, plus (currently) a 0.01 BTC network transaction fee.
21% "spend" fee? What are they Paypal 2.0. No reason for fees to be that high given there is absolutely no risk to any processor. – DeathAndTaxes – 2011-10-06T20:18:45.957
1% is not a lot considering the infrastructure required to host an application like StrongCoin. With StrongCoin you can always export your private key and make payments another way. – Ian Purton – 2011-10-07T20:22:14.173
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From https://www.casascius.com :
...you can enter (or "import") your coin's private key code directly into Bitcoin clients such as Armory, Blockchain.info, or directly into Mt. Gox as a deposit method.
Mt. Gox is dead long since; Blockchain doesn't recognize them any more. – vv01f – 2017-05-07T16:48:58.983
2For the love of humanity, nobody do this. Casascius coins are quite collectible. If you want to redeem your coins, for bitcoins, sell them on eBay or offer them in an "auction" on a site like bitcointalk.org. Do your research before you cash out. A 1 BTC Casascius coin is worth a lot more than 1 BTC. – RLH – 2013-11-13T20:03:44.333
My head slightly hurts from all the "real (virtual) vs physical". – ripper234 – 2011-09-07T03:16:37.640