Bitcoin Wiki - User contributions [en]

Mini private key format

2012-08-20T12:08:03Z

Nikos 1993: /* Python Code */

[[Image:QR-privkeys-sidebyside.png|thumb|right|QR codes of the same private key, in mini versus regular private key format. Both codes have the same dot density and error correction level, but the mini key is 57% of the full code's size.]]
The '''mini private key format''' is a method of encoding a Bitcoin private key in as few as 30 characters so that it can be embedded in a small space. This private key format was first used in Casascius physical bitcoins, and is also favorable for use in QR codes. The fewer characters encoded in a QR code, the lower dot density can be used, as well as more dots allocated to error correction in the same space, significantly improving readability and resistance to damage. The mini private key format offers its own built-in check code as a small margin of protection against typos.

An example key using this encoding is '''S6c56bnXQiBjk9mqSYE7ykVQ7NzrRy'''.

==Usage on a physical bitcoin==
The way it might appear within a physical bitcoin is on a round card printed as follows:

Side of discs showing mini private key: (from [[Casascius physical bitcoins]])<br/>
[[Image:Miniprivkeys.jpg|300px]]

Side of discs showing prefix of bitcoin address (printed on the opposite side):<br/>
[[Image:Minipubkeys.jpg|300px]]

The examples in this article use the private key and Bitcoin address of the leftmost circle in the above two photos.

==Import==
Mini private keys can be imported through the following clients/services:

===Applications===
* [[Armory]]

The current mainline ("Satoshi") client cannot currently be used to import minikeys.

===Mobile===

* Mt. Gox Mobile can redeem a private key scanned from a QR Code or is entered using the keyboard. Upon importing, Mt. Gox sweeps the funds to a secondary address, and then a user must wait for six confirmations before the funds will appear in the Mt. Gox account.

===Web===

* [[Blockchain.info]]
** Private keys can be imported into a Blockchain.info wallet and bitcoins can be sent to another address immediately upon import without needing to wait for any confirmations. Even after import, funds remain associated with the private key until they are actually spent to a different address.
* [[Strongcoin]]
* [[Mt. Gox]]
** Importing minikeys is done through the deposit screen using the "Import Private Key" deposit method. Upon importing, Mt. Gox sweeps the funds to a secondary address, and then a user must wait for six confirmations before the funds will appear in the Mt. Gox account. Removing the imported bitcoins from the Mt. Gox account is treated as a bitcoin withdrawal and counts against daily/monthly limits.
** Mt. Gox also permanently remembers any imported private key and automatically sweeps any future funds sent to it into the user's Mt. Gox account.
** Mt. Gox's import screen doesn't properly detect or reject typos. If you make a mistake, Mt. Gox will treat it as a valid entry and report that a private key with a balance of 0.00 BTC from a bitcoin address you won't recognize was "successfully" imported.

==Decoding==
The private key encoding consists of 30 alphanumeric characters from the [[base58]] alphabet used in Bitcoin. The first of the characters is always the uppercase letter S.

A simple test must be performed to determine which method shall be used:

# Add a question mark to the end of the mini private key string.
# Take the SHA256 hash of the entire string. However, we will only looking at the first two bytes of the result.
# If the first byte is 00, the string is a well-formed minikey. If the first byte is not 00, the string should be rejected as a minikey.

===Example with SHA256===
Here is an example with the sample private key S6c56bnXQiBjk9mqSYE7ykVQ7NzrRy.

The string "S6c56bnXQiBjk9mqSYE7ykVQ7NzrRy?" has a SHA256 value that begins with 00, so it is well-formed.

To obtain the full 256-bit private key, simply take the SHA256 hash of the entire string. There is no encoding for breaks in the string even if printed that way - the SHA256 should be taken of exactly thirty bytes.

SHA256("S6c56bnXQiBjk9mqSYE7ykVQ7NzrRy") = 4C7A9640C72DC2099F23715D0C8A0D8A35F8906E3CAB61DD3F78B67BF887C9AB

This sample key in [[wallet export format]] is 5JPy8Zg7z4P7RSLsiqcqyeAF1935zjNUdMxcDeVrtU1oarrgnB7, and the corresponding [[Bitcoin address]] is 1CciesT23BNionJeXrbxmjc7ywfiyM4oLW.

==Check code==
The mini private key format offers a simple typo check code. Mini private keys must be generated in a "brute force" fashion, keeping only keys that conform to the format's rules. If a key is well-formed (30 Base58 characters starting with S), but fails the hash check, then it probably contains a typo.

If the SHA256 hash of the string followed by '?' doesn't result in something that begins with 0x00, the mini private key is not valid.

==Creating mini private keys==
Creating mini private keys is relatively simple. One program which can create such keys is [[Casascius Bitcoin Utility]].

Mini private keys must be created "from scratch", as the conversion from mini private key to full-size private key is one-way. In other words, there is no way to convert an existing full-size private key into a mini private key.

To create mini private keys, simply create random strings that satisfy the well-formedness requirement, and then eliminate the ones that do not pass the typo check. (This means eliminating more than 99% of the candidates.) Then use the appropriate algorithm to compute the corresponding private key, and in turn, the matching Bitcoin address. The Bitcoin address can always be computed from just the private key.

It is strongly advisable to avoid using the digit "1" in minikeys unless it is being printed in such a way where a user is unlikely to mistake it for the lowercase letter "l". Few clients and redemption tools are prepared to tell the user that their entry containing the letter "l" should actually be the number "1" - rather, they will simply reject the code and may leave the user confused.

In all cases, you '''must''' use a secure cryptographic random number generator to eliminate risks of predictability of the random strings.

==Casascius Series 1 coins==

Casascius Series 1 Physical Bitcoins use a 22-character variant of the minikey format, instead of 30 characters. Everything is the same other than the length. To properly implement minikey redemption, services and clients MUST support the 30-character format, but MAY support the 22-character format as well. Use of the 22-character format for future applications is discouraged due to security considerations.

==Python Code==
The following code produces sample 22-character (weaker than 30-character) SHA256-based mini private keys in Python. For real-world use, ''random'' must be replaced with a better source of entropy, as the Python documentation for ''random'' states the function ''"is completely unsuitable for cryptographic purposes"''.

<source lang="python">
import random
import hashlib

BASE58 = '123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz'

def Candidate():
"""
Generate a random, well-formed mini private key.
"""
return('%s%s' % ('S', ''.join(
[BASE58[ random.randrange(0,len(BASE58)) ] for i in range(21)])))

def GenerateKeys(numKeys = 10):
"""
Generate mini private keys and output the mini key as well as the full
private key. numKeys is The number of keys to generate, and
"""
keysGenerated = 0
totalCandidates = 0
while keysGenerated < numKeys:
try:
cand = Candidate()
# Do typo check
t = '%s?' % cand
# Take one round of SHA256
candHash = hashlib.sha256(t).digest()
# Check if the first eight bits of the hash are 0
if candHash[0] == '\x00':
privateKey = GetPrivateKey(cand)
print('\n%s\nSHA256( ): %s\nsha256(?): %s' %
(cand, privateKey, candHash.encode('hex_codec')))
if CheckShortKey(cand):
print('Validated.')
else:
print('Invalid!')
keysGenerated += 1
totalCandidates += 1
except KeyboardInterrupt:
break
print('\n%s: %i\n%s: %i\n%s: %r\n%s: %.1f' %
('Keys Generated', keysGenerated,
'Total Candidates', totalCandidates,
'Additional Security', additionalSecurity,
'Reject Percentage',
100*(1.0-keysGenerated/float(totalCandidates))))

def GetPrivateKey(shortKey):
"""
Returns the hexadecimal representation of the private key corresponding
to the given short key.
"""
if CheckShortKey(shortKey):
return hashlib.sha256(shortKey).hexdigest()
else:
print('Typo detected in private key!')
return None

def CheckShortKey(shortKey):
"""
Checks for typos in the short key.
"""
if len(shortKey) != 22:
return False
t = '%s?' % shortKey
tHash = hashlib.sha256(t).digest()
# Check to see that first byte is \x00
if tHash[0] == '\x00':
return True
return False
</source>

Mini private key format

2012-08-20T12:07:20Z

Nikos 1993:

[[Image:QR-privkeys-sidebyside.png|thumb|right|QR codes of the same private key, in mini versus regular private key format. Both codes have the same dot density and error correction level, but the mini key is 57% of the full code's size.]]
The '''mini private key format''' is a method of encoding a Bitcoin private key in as few as 30 characters so that it can be embedded in a small space. This private key format was first used in Casascius physical bitcoins, and is also favorable for use in QR codes. The fewer characters encoded in a QR code, the lower dot density can be used, as well as more dots allocated to error correction in the same space, significantly improving readability and resistance to damage. The mini private key format offers its own built-in check code as a small margin of protection against typos.

An example key using this encoding is '''S6c56bnXQiBjk9mqSYE7ykVQ7NzrRy'''.

==Usage on a physical bitcoin==
The way it might appear within a physical bitcoin is on a round card printed as follows:

Side of discs showing mini private key: (from [[Casascius physical bitcoins]])<br/>
[[Image:Miniprivkeys.jpg|300px]]

Side of discs showing prefix of bitcoin address (printed on the opposite side):<br/>
[[Image:Minipubkeys.jpg|300px]]

The examples in this article use the private key and Bitcoin address of the leftmost circle in the above two photos.

==Import==
Mini private keys can be imported through the following clients/services:

===Applications===
* [[Armory]]

The current mainline ("Satoshi") client cannot currently be used to import minikeys.

===Mobile===

* Mt. Gox Mobile can redeem a private key scanned from a QR Code or is entered using the keyboard. Upon importing, Mt. Gox sweeps the funds to a secondary address, and then a user must wait for six confirmations before the funds will appear in the Mt. Gox account.

===Web===

* [[Blockchain.info]]
** Private keys can be imported into a Blockchain.info wallet and bitcoins can be sent to another address immediately upon import without needing to wait for any confirmations. Even after import, funds remain associated with the private key until they are actually spent to a different address.
* [[Strongcoin]]
* [[Mt. Gox]]
** Importing minikeys is done through the deposit screen using the "Import Private Key" deposit method. Upon importing, Mt. Gox sweeps the funds to a secondary address, and then a user must wait for six confirmations before the funds will appear in the Mt. Gox account. Removing the imported bitcoins from the Mt. Gox account is treated as a bitcoin withdrawal and counts against daily/monthly limits.
** Mt. Gox also permanently remembers any imported private key and automatically sweeps any future funds sent to it into the user's Mt. Gox account.
** Mt. Gox's import screen doesn't properly detect or reject typos. If you make a mistake, Mt. Gox will treat it as a valid entry and report that a private key with a balance of 0.00 BTC from a bitcoin address you won't recognize was "successfully" imported.

==Decoding==
The private key encoding consists of 30 alphanumeric characters from the [[base58]] alphabet used in Bitcoin. The first of the characters is always the uppercase letter S.

A simple test must be performed to determine which method shall be used:

# Add a question mark to the end of the mini private key string.
# Take the SHA256 hash of the entire string. However, we will only looking at the first two bytes of the result.
# If the first byte is 00, the string is a well-formed minikey. If the first byte is not 00, the string should be rejected as a minikey.

===Example with SHA256===
Here is an example with the sample private key S6c56bnXQiBjk9mqSYE7ykVQ7NzrRy.

The string "S6c56bnXQiBjk9mqSYE7ykVQ7NzrRy?" has a SHA256 value that begins with 00, so it is well-formed.

To obtain the full 256-bit private key, simply take the SHA256 hash of the entire string. There is no encoding for breaks in the string even if printed that way - the SHA256 should be taken of exactly thirty bytes.

SHA256("S6c56bnXQiBjk9mqSYE7ykVQ7NzrRy") = 4C7A9640C72DC2099F23715D0C8A0D8A35F8906E3CAB61DD3F78B67BF887C9AB

This sample key in [[wallet export format]] is 5JPy8Zg7z4P7RSLsiqcqyeAF1935zjNUdMxcDeVrtU1oarrgnB7, and the corresponding [[Bitcoin address]] is 1CciesT23BNionJeXrbxmjc7ywfiyM4oLW.

==Check code==
The mini private key format offers a simple typo check code. Mini private keys must be generated in a "brute force" fashion, keeping only keys that conform to the format's rules. If a key is well-formed (30 Base58 characters starting with S), but fails the hash check, then it probably contains a typo.

If the SHA256 hash of the string followed by '?' doesn't result in something that begins with 0x00, the mini private key is not valid.

==Creating mini private keys==
Creating mini private keys is relatively simple. One program which can create such keys is [[Casascius Bitcoin Utility]].

Mini private keys must be created "from scratch", as the conversion from mini private key to full-size private key is one-way. In other words, there is no way to convert an existing full-size private key into a mini private key.

To create mini private keys, simply create random strings that satisfy the well-formedness requirement, and then eliminate the ones that do not pass the typo check. (This means eliminating more than 99% of the candidates.) Then use the appropriate algorithm to compute the corresponding private key, and in turn, the matching Bitcoin address. The Bitcoin address can always be computed from just the private key.

It is strongly advisable to avoid using the digit "1" in minikeys unless it is being printed in such a way where a user is unlikely to mistake it for the lowercase letter "l". Few clients and redemption tools are prepared to tell the user that their entry containing the letter "l" should actually be the number "1" - rather, they will simply reject the code and may leave the user confused.

In all cases, you '''must''' use a secure cryptographic random number generator to eliminate risks of predictability of the random strings.

==Casascius Series 1 coins==

Casascius Series 1 Physical Bitcoins use a 22-character variant of the minikey format, instead of 30 characters. Everything is the same other than the length. To properly implement minikey redemption, services and clients MUST support the 30-character format, but MAY support the 22-character format as well. Use of the 22-character format for future applications is discouraged due to security considerations.

==Python Code==
The following code produces sample SHA256-based mini private keys in Python. For real-world use, ''random'' must be replaced with a better source of entropy, as the Python documentation for ''random'' states the function ''"is completely unsuitable for cryptographic purposes"''.

<source lang="python">
import random
import hashlib

BASE58 = '123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz'

def Candidate():
"""
Generate a random, well-formed mini private key.
"""
return('%s%s' % ('S', ''.join(
[BASE58[ random.randrange(0,len(BASE58)) ] for i in range(21)])))

def GenerateKeys(numKeys = 10):
"""
Generate mini private keys and output the mini key as well as the full
private key. numKeys is The number of keys to generate, and
"""
keysGenerated = 0
totalCandidates = 0
while keysGenerated < numKeys:
try:
cand = Candidate()
# Do typo check
t = '%s?' % cand
# Take one round of SHA256
candHash = hashlib.sha256(t).digest()
# Check if the first eight bits of the hash are 0
if candHash[0] == '\x00':
privateKey = GetPrivateKey(cand)
print('\n%s\nSHA256( ): %s\nsha256(?): %s' %
(cand, privateKey, candHash.encode('hex_codec')))
if CheckShortKey(cand):
print('Validated.')
else:
print('Invalid!')
keysGenerated += 1
totalCandidates += 1
except KeyboardInterrupt:
break
print('\n%s: %i\n%s: %i\n%s: %r\n%s: %.1f' %
('Keys Generated', keysGenerated,
'Total Candidates', totalCandidates,
'Additional Security', additionalSecurity,
'Reject Percentage',
100*(1.0-keysGenerated/float(totalCandidates))))

def GetPrivateKey(shortKey):
"""
Returns the hexadecimal representation of the private key corresponding
to the given short key.
"""
if CheckShortKey(shortKey):
return hashlib.sha256(shortKey).hexdigest()
else:
print('Typo detected in private key!')
return None

def CheckShortKey(shortKey):
"""
Checks for typos in the short key.
"""
if len(shortKey) != 22:
return False
t = '%s?' % shortKey
tHash = hashlib.sha256(t).digest()
# Check to see that first byte is \x00
if tHash[0] == '\x00':
return True
return False
</source>

Casascius physical bitcoins

2012-08-20T12:06:28Z

Nikos 1993:

[[Image:Casascius 25btc size compare.jpg|thumb|right|300px|Various views of Casascius coins]]
[[File:Physbitcoinkey.jpg|thumb|right|Redeemed Casascius coin]]
'''Casascius physical bitcoins''', also called '''Casascius coins''', are physical metal coins created by Bitcoin user [[User:Casascius|Casascius]] (Mike Caldwell, Sandy, Utah, USA) 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, https://www.casascius.com (only Bitcoin accepted), or at http://www.MemoryDealers.com (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 a private key gets the value on the coin, and afterwards, the coin no longer has any Bitcoin value. However, 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 at [[MtGox]] (via the ''Add Funds - Redeem Private Key'' screen), as well as with a patched Bitcoin client.

Casascius coins are similar to [[Bitbills]] in that they are an object that contains a redemption code that serves as a bearer item for digital bitcoins.

An independent website called [[Casascius Bitcoin Analyzer]] (http://www.uberbills.com) tracks the status of all Casascius coins in circulation, based on information from the block chain, as well as

==Releases of Casascius coins==

===Original series 1 BTC coin===
* 1.125 inches in diameter
* Solid brass
* Year printed on coins: 2011
* Approximately 0.24 ounces
* Eight-digit "[[firstbits]]" inkjetted onto surface of hologram sticker
* First appeared in September 2011<ref>[http://bitcointalk.org/index.php?topic=41892.0 CASASCIUS PHYSICAL BITCOIN - In Stock Now!]</ref>.
* 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===
[[Image:Casascius-series-2.jpg|thumb|right|200px|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.
* 1.125 inches in diameter
* Solid brass
* Year printed on coins: 2011
* Approximately 0.24 ounces
* 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)
* First appeared in November 2011
* No spelling error in hologram

===10 BTC silver round===
* First available on Dec 1, 2011
* 39mm diameter
* 1 troy ounce .999 Fine Silver
* 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===
[[Image:Casascius 25btc.jpg|thumb|right|Casascius 25BTC 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
* First appeared in October 2011
* Zeroes and ones on the back encode the message "You asked for change, we gave you coins"

===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===
* Weight: 4.2oz
* Dimensions: 8cm x 4cm x 0.6cm
* Hologram: V1
* Printed year: none
* 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===
* Available as of Dec 16, 2011
* Printed year: 2012
* Diameter: 30mm
* 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

== See also ==
* [[Mini private key format]]

== References ==
<references />

[[Category:Physical bitcoins]]

Casascius physical bitcoins

2012-08-20T12:05:25Z

Nikos 1993:

[[Image:Casascius 25btc size compare.jpg|thumb|right|300px|Various views of Casascius coins]]
[[File:Physbitcoinkey.jpg|thumb|right|Redeemed Casascius coin]]
[[File:Miniprivkeys.jpg|right]]
[[File:Minipubkeys.jpg|right]]
'''Casascius physical bitcoins''', also called '''Casascius coins''', are physical metal coins created by Bitcoin user [[User:Casascius|Casascius]] (Mike Caldwell, Sandy, Utah, USA) 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, https://www.casascius.com (only Bitcoin accepted), or at http://www.MemoryDealers.com (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 a private key gets the value on the coin, and afterwards, the coin no longer has any Bitcoin value. However, 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 at [[MtGox]] (via the ''Add Funds - Redeem Private Key'' screen), as well as with a patched Bitcoin client.

Casascius coins are similar to [[Bitbills]] in that they are an object that contains a redemption code that serves as a bearer item for digital bitcoins.

An independent website called [[Casascius Bitcoin Analyzer]] (http://www.uberbills.com) tracks the status of all Casascius coins in circulation, based on information from the block chain, as well as

==Releases of Casascius coins==

===Original series 1 BTC coin===
* 1.125 inches in diameter
* Solid brass
* Year printed on coins: 2011
* Approximately 0.24 ounces
* Eight-digit "[[firstbits]]" inkjetted onto surface of hologram sticker
* First appeared in September 2011<ref>[http://bitcointalk.org/index.php?topic=41892.0 CASASCIUS PHYSICAL BITCOIN - In Stock Now!]</ref>.
* 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===
[[Image:Casascius-series-2.jpg|thumb|right|200px|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.
* 1.125 inches in diameter
* Solid brass
* Year printed on coins: 2011
* Approximately 0.24 ounces
* 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)
* First appeared in November 2011
* No spelling error in hologram

===10 BTC silver round===
* First available on Dec 1, 2011
* 39mm diameter
* 1 troy ounce .999 Fine Silver
* 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===
[[Image:Casascius 25btc.jpg|thumb|right|Casascius 25BTC 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
* First appeared in October 2011
* Zeroes and ones on the back encode the message "You asked for change, we gave you coins"

===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===
* Weight: 4.2oz
* Dimensions: 8cm x 4cm x 0.6cm
* Hologram: V1
* Printed year: none
* 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===
* Available as of Dec 16, 2011
* Printed year: 2012
* Diameter: 30mm
* 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

==References==
<references />

[[Category:Physical bitcoins]]

Casascius physical bitcoins

2012-08-20T11:52:45Z

Nikos 1993: +redeemed picture

[[Image:Casascius 25btc size compare.jpg|thumb|right|300px|Various views of Casascius coins]]
[[File:Physbitcoinkey.jpg|thumb|right|Redeemed Casascius coin]]
'''Casascius physical bitcoins''', also called '''Casascius coins''', are physical metal coins created by Bitcoin user [[User:Casascius|Casascius]] (Mike Caldwell, Sandy, Utah, USA) 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, https://www.casascius.com (only Bitcoin accepted), or at http://www.MemoryDealers.com (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 a private key gets the value on the coin, and afterwards, the coin no longer has any Bitcoin value. However, 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 at [[MtGox]] (via the ''Add Funds - Redeem Private Key'' screen), as well as with a patched Bitcoin client.

Casascius coins are similar to [[Bitbills]] in that they are an object that contains a redemption code that serves as a bearer item for digital bitcoins.

An independent website called [[Casascius Bitcoin Analyzer]] (http://www.uberbills.com) tracks the status of all Casascius coins in circulation, based on information from the block chain, as well as

==Releases of Casascius coins==

===Original series 1 BTC coin===
* 1.125 inches in diameter
* Solid brass
* Year printed on coins: 2011
* Approximately 0.24 ounces
* Eight-digit "[[firstbits]]" inkjetted onto surface of hologram sticker
* First appeared in September 2011<ref>[http://bitcointalk.org/index.php?topic=41892.0 CASASCIUS PHYSICAL BITCOIN - In Stock Now!]</ref>.
* 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===
[[Image:Casascius-series-2.jpg|thumb|right|200px|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.
* 1.125 inches in diameter
* Solid brass
* Year printed on coins: 2011
* Approximately 0.24 ounces
* 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)
* First appeared in November 2011
* No spelling error in hologram

===10 BTC silver round===
* First available on Dec 1, 2011
* 39mm diameter
* 1 troy ounce .999 Fine Silver
* 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===
[[Image:Casascius 25btc.jpg|thumb|right|Casascius 25BTC 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
* First appeared in October 2011
* Zeroes and ones on the back encode the message "You asked for change, we gave you coins"

===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===
* Weight: 4.2oz
* Dimensions: 8cm x 4cm x 0.6cm
* Hologram: V1
* Printed year: none
* 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===
* Available as of Dec 16, 2011
* Printed year: 2012
* Diameter: 30mm
* 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

==References==
<references />

[[Category:Physical bitcoins]]

File:Physbitcoinkey.jpg

2012-08-20T11:50:54Z

Nikos 1993: Source: http://img199.imageshack.us/img199/6272/physbitcoinkey.jpg

Source: http://img199.imageshack.us/img199/6272/physbitcoinkey.jpg