Bitcoin and Blockchain

Physical Bitcoins

Various views of Casascius coins

, also called Casascius coins, are physical metal coins created by Bitcoin user Casascius (Mike Caldwell, Sandy, Utah, USA) and sold until Nov 26, 2013, that contain an embedded piece of paper with digital Bitcoin value, covered by a tamper-resistant hologram. Casascius coins are available in 1, 10, 25, 100, and 1000 BTC increments. They can be purchased at Casascius's website, (only Bitcoin accepted), or at (PayPal and credit cards accepted).

The coins are designed such that they could be circulated in face-to-face transactions. The first person to redeem its private key gets the value on the coin, and afterwards, the coin no longer has any Bitcoin value. It is difficult or impossible to read the private key on the coin without damaging or destroying the hologram, which exposes a honeycomb-like tamper-evidence pattern when peeled.

The piece of paper inside each coin has a private key which forms the backing for the Bitcoin value represented by the coin. Redeeming the private key back into digital Bitcoins is currently available with a patched reference client and many of the alternative clients.

There are 2 independent websites that track the status of all Casascius coins in circulation, based on information from the block chain:

Original series 1 BTC coin

• 1.125 inches in diameter
• Solid brass
• Year printed on coins: 2011
• Approximately 0.24 ounces
• Private key: 22 character string inside the coin, the 256-bit private key is SHA256(string)
• Approximate number produced: 3, 500 as of November 2011
• A spelling error can be found in the small lettering of the hologram: "CASACIUS" instead of "CASASCIUS"
• Casascius has stated that no more than 11, 000 may be produced
• All 11, 000 Bitcoin addresses pre-generated for the series have been published as a signed text file

Second series 1 BTC coin

Second series 1 BTC Casascius coin

The hologram and the private key is different, the metal part of the coin is the same as the first series.

• Denomination ("ONE BTC") appears on the hologram
• Eight-digit "firstbits" visible through a small transparent window that allows limited visibility of one side of the private key paper
• Private key: 30 character string inside the coin, the 256-private key is SHA256(string)

10 BTC silver round

• Uses second series holograms marked TEN BTC
• Comes in a clear plastic capsule
• Zeroes and ones on the back encode the message "Bitcoin: an idea too big to fail"

25 BTC coin

• 1.75 inches in diameter, about 3mm thick
• Gold-plated alloy
• Approximately 1.2 ounces
• Printed year: 2011
• Uses same holograms and private key scheme as original series 1 BTC coin

100 BTC gold plated bar

• Weight: 4.2oz
• Dimensions: 8cm x 4cm x 0.6cm
• Printed year: none
• Indented features: "100 BTC", Bitcoin logo, "gold plated bearer bar"
• Hologram: V1 or V2

1000 BTC gold plated bar

• Hologram: V1
• Lasered overprinting on the hologram to indicate the denomination
• This is a non-denominated bar that has been engraved with a 1000 BTC denomination. It is indented with the Bitcoin logo and the words "gold plated bearer bar" like the 100 BTC bar, but is not indented with a denomination. The denomination is applied via laser engraving.
• This item is presently listed for sale only through MemoryDealers.com

1000 BTC 1 troy ounce gold coin

• Special order item, 3 business day lead time
• Hologram: V1 with Bitcoin address lasered at top instead of inkjetted across middle
• Availability: Purchase from MemoryDealers.com, or directly from Casascius with BTC, or USD bank wire

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