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@ -189,252 +189,9 @@ More recent implementations of colored coins use the +OP_RETURN+ script
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opcode to store metadata in a transaction, in conjunction with external
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data stores that associate the metadata to specific assets.
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((("Open Assets")))The two most prominent implementations of colored
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coins today are http://www.openassets.org/[_Open Assets_] and
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http://coloredcoins.org[_Colored Coins by Colu_]. These two systems use
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different approaches to colored coins and are not compatible. Colored
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coins created in one system cannot be seen or used in the other system.
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==== Using Colored Coins
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Colored coins are created, transferred, and generally viewed in special
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wallets that can interpret the colored coins protocol metadata attached
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to bitcoin transactions. Special care must be taken to avoid using a
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colored-coin–related key in a regular bitcoin wallet, as the
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regular wallet may destroy the metadata. Similarly, colored coins should
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not be sent to addresses managed by regular wallets, but only to
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addresses that are managed by wallets that are colored-coin-aware. Both
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Colu and Open Assets systems use special colored-coin addresses to
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mitigate this risk and to ensure that colored coins are not sent to
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unaware wallets.
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Colored coins are also not visible to most general-purpose blockchain
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explorers. Instead, you must use a colored-coins explorer to interpret
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the metadata of a colored coins transaction.
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An Open Assets-compatible wallet application and blockchain explorer can
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be found at https://www.coinprism.info[coinprism].
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A Colu Colored Coins-compatible wallet application and blockchain
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explorer can be found at http://coloredcoins.org/explorer/[Blockchain
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Explorer].
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A Copay wallet plug-in can be found at
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http://coloredcoins.org/colored-coins-copay-addon/[Colored Coins Copay
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Addon].
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==== Issuing Colored Coins
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Each of the colored coins implementations has a different way of
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creating colored coins, but they all provide similar functionality. The
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process of creating a colored coin asset is called _issuance_. An
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initial transaction, the _issuance transaction_ registers the asset on
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the bitcoin blockchain and creates an _asset ID_ that is used to
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reference the asset. Once issued, assets can be transferred between
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addresses using _transfer transactions_.
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Assets issued as colored coins can have multiple properties. They can be
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_divisible_ or _indivisible_, meaning that the amount of asset in a
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transfer can be an integer (e.g., 5) or have decimal subdivision (e.g.,
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4.321). Assets can also have _fixed issuance_, meaning a certain amount
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are issued only once, or can be _reissued_, meaning that new units of
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the asset can be issued by the original issuer after the initial
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issuance.
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Finally, some colored coins enable _dividends_, allowing the
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distribution of bitcoin payments to the owners of a colored coin asset
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in proportion to their ownership.
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==== Colored Coins Transactions
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The metadata that gives meaning to a colored coin transaction is usually
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stored in one of the outputs using the +OP_RETURN+ opcode. Different
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colored coins protocols use different encodings for the content of the
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+OP_RETURN+ data. The output containing the +OP_RETURN+ is called the
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_marker output_.
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The order of the outputs and position of the marker output may have
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special meaning in the colored coins protocol. In Open Assets, for
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example, any outputs before the marker output represent asset issuance.
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Any outputs after the marker represent asset transfer. The marker output
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assigns specific values and colors to the other outputs by referencing
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their order in the transaction.
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In Colored Coins (Colu), by comparison, the marker output encodes an
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opcode that determines how the metadata is interpreted. Opcodes 0x01
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through 0x0F indicate an issuance transaction. An issuance opcode is
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usually followed by an asset ID or other identifier that can be used to
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retrieve the asset information from an external source (e.g.,
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bittorrent). Opcodes 0x10 through 0x1F represent a transfer
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transaction. Transfer transaction metadata contain simple scripts that
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transfer specific amounts of assets from inputs to outputs, by reference
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to their index. Ordering of inputs and outputs is therefore important in
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the interpretation of the script.
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If the metadata is too long to fit in +OP_RETURN+, the colored coins
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protocol may use other "tricks" to store metadata in a transaction.
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Examples include putting metadata in a redeem script, followed by
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+OP_DROP+ opcodes to ensure the script ignores the metadata. Another
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mechanism used is a 1-of-N multisig script where only the first public
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key is a real public key that can spend the output and subsequent "keys"
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are replaced by encoded metadata.
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In order to correctly interpret the metadata in a colored coins
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transaction you must use a compatible wallet or block explorer.
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Otherwise, the transaction looks like a "normal" bitcoin transaction
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with an +OP_RETURN+ output.
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As an example, I created and issued a MasterBTC asset using colored
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coins. The MasterBTC asset represents a voucher for a free copy of this
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book. These vouchers can be transferred, traded, and redeemed using a
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colored coins-compatible wallet.
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For this particular example, I used the wallet and explorer at
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http://coinprism.info/[_https://coinprism.info_], which uses the Open
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Assets colored coins protocol.
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<<the_issuance_transaction_as_viewed_on_coinprismio>> shows the issuance
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transaction using the Coinprism block explorer:
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https://www.coinprism.info/tx/10d7c4e022f35288779be6713471151ede967caaa39eecd35296aa36d9c109ec[https://www.coinprism.info/tx/10d7c4e022f35288779be6713471151ede967caaa39eecd35296aa36d9c109ec])
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[[the_issuance_transaction_as_viewed_on_coinprismio]]
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.The issuance transaction as viewed on coinprism.info
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image::images/mbc2_1201.png[The Issuance Transaction - as viewed on coinprism.info]
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As you can see, coinprism shows the issuance of 20 units of "Free copy
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of Mastering Bitcoin," the MasterBTC asset, to a special colored coin
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address:
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=== RGB
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----
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akTnsDt5uzpioRST76VFRQM8q8sBFnQiwcx
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----
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[WARNING]
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====
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Any funds or colored assets sent to this address will be lost forever.
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Do not send value to this example address!
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====
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((("transaction IDs (txid)")))The transaction ID of the issuance
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transaction is a "normal" bitcoin transaction ID.
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<<the_issuance_transaction_on_a_block>> shows that same transaction in a
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block explorer that doesn't decode colored coins. We'll use
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_blockchain.info_:
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https://blockchain.info/tx/10d7c4e022f35288779be6713471151ede967caaa39eecd35296aa36d9c109ec[https://blockchain.info/tx/10d7c4e022f35288779be6713471151ede967caaa39eecd35296aa36d9c109ec]
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[[the_issuance_transaction_on_a_block]]
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.The issuance transaction on a block explorer that doesn't decode colored coins
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image::images/mbc2_1202.png[The Issuance Transaction - on a block explorer that doesn't decode colored coins]
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As you can see, _blockchain.info_ doesn't recognize this as a colored
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coins transaction. In fact, it marks the second output with "Unable to
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decode output address" in red letters.
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If you select "Show scripts & coinbase" on that screen, you can see
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more detail about the transaction
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(<<the_scripts_in_the_issuance_transaction>>).
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[[the_scripts_in_the_issuance_transaction]]
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.The scripts in the issuance transaction
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image::images/mbc2_1203.png[The scripts in the Issuance Transaction]
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Once again, _blockchain.info_ doesn't understand the second output. It
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marks it with "Strange" in red letters. However, we can see that some of
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the metadata in the marker output is human-readable:
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----
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OP_RETURN 4f41010001141b753d68747470733a2f2f6370722e736d2f466f796b777248365559
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(decoded) "OA____u=https://cpr.sm/FoykwrH6UY
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----
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Let's retrieve the transaction using +bitcoin-cli+:
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----
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$ bitcoin-cli decoderawtransaction `bitcoin-cli getrawtransaction 10d7c4e022f35288779be6713471151ede967caaa39eecd35296aa36d9c109ec`
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----
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Stripping out the rest of the transaction, the second output looks like
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this:
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[role="pagebreak-before"]
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[source,json]
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----
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{
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"value": 0.00000000,
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"n": 1,
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"scriptPubKey": "OP_RETURN 4f41010001141b753d68747470733a2f2f6370722e736d2f466f796b777248365559"
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}
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----
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The prefix +4F41+ represents the letters "OA", which stands for "Open
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Assets" and helps us identify that what follows is metadata defined by
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the Open Assets protocol. The ASCII-encoded string that follows is a
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link to an asset definition:
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----
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u=https://cpr.sm/FoykwrH6UY
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----
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((("", startref="color12")))((("", startref="BCAcoins12")))If we
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retrieve this URL, we get a JSON-encoded asset definition, as shown
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here:
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[source,json]
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----
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{
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"asset_ids": [
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"AcuRVsoa81hoLHmVTNXrRD8KpTqUXeqwgH"
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],
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"contract_url": null,
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"name_short": "MasterBTC",
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"name": "Free copy of \"Mastering Bitcoin\"",
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"issuer": "Andreas M. Antonopoulos",
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"description": "This token is redeemable for a free copy of the book \"Mastering Bitcoin\"",
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"description_mime": "text/x-markdown; charset=UTF-8",
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"type": "Other",
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"divisibility": 0,
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"link_to_website": false,
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"icon_url": null,
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"image_url": null,
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"version": "1.0"
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}
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----
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=== Counterparty
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((("blockchain applications",
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"Counterparty")))((("Counterparty")))((("smart contracts")))((("Ethereum
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Virtual Machine (EVM)")))((("extrinsic asset management")))((("virtual
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asset management")))Counterparty is a protocol layer built on top of
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bitcoin. The Counterparty protocol, similar to colored coins, offers the
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ability to create and trade virtual assets and tokens. In addition,
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Counterparty offers a decentralized exchange for assets. Counterparty is
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also implementing smart contracts, based on the Ethereum Virtual Machine
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(EVM).
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Like the colored coins protocols, Counterparty embeds metadata in
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bitcoin transactions, using the +OP_RETURN+ opcode or 1-of-N
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multisignature addresses that encode metadata in the place of public
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keys. Using these mechanisms, Counterparty implements a protocol layer
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encoded in bitcoin transactions. The additional protocol layer can be
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interpreted by applications that are Counterparty-aware, such as wallets
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and blockchain explorers, or any application built using the
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Counterparty libraries.
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((("digital ownership")))Counterparty can be used as a platform for
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other applications and services, in turn. For example, Tokenly is a
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platform built on top of Counterparty that allows content creators,
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artists, and companies to issue tokens that express digital ownership
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and can be used to rent, access, trade, or shop for content, products,
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and services. Other applications leveraging Counterparty include games
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(Spells of Genesis) and grid computing projects (Folding Coin).
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More details about Counterparty can be found at https://counterparty.io.
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The open source project can be found at
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https://github.com/CounterpartyXCP[].
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//FIXME
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[[state_channels]]
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=== Payment Channels and State Channels
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David A. Harding
11 months ago