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88 lines
3.5 KiB
ReStructuredText
88 lines
3.5 KiB
ReStructuredText
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.. Copyright BigchainDB GmbH and BigchainDB contributors
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SPDX-License-Identifier: (Apache-2.0 AND CC-BY-4.0)
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Code is Apache-2.0 and docs are CC-BY-4.0
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=================
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Advanced Examples
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=================
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Crypto Conditions
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-----------------
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Let's start with a basic use case example. Alice bought a bicycle for €240.
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She will use the bike for a year and will give it to her daughter afterwards.
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First, we create an asset registering the bicycle:
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.. code-block:: js
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const txCreateAliceSimple = driver.Transaction.makeCreateTransaction(
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{'asset': 'bicycle'},
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{'purchase_price': '€240'},
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[
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driver.Transaction.makeOutput(driver.Transaction.makeEd25519Condition(alice.publicKey))
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],
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alice.publicKey
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)
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const txCreateAliceSimpleSigned = driver.Transaction.signTransaction(txCreateAliceSimple, alice.privateKey)
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After a year, she decides it's time to transfer the bicycle to her daughter Carly.
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However, Alice wants to maintain the right over the bike so she can possibly sell it. If she would transfer the bicycle to Carly, she won't be able to do this.
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So, Alice needs a crypto conditions that defines that she or her daughter can sign the ``TRANSFER`` transaction to a possible buyer.
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We need to define a threshold as well. This defines how many persons have to sign the transaction to ``TRANSFER`` it.
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In this case, we define two subconditions with the public keys from Alice and Carly. Next, we set the threshold to **one**.
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This means that just one of the subconditions has to sign the transaction to transfer it.
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This can be the mother Alice, or Carly herself.
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.. code-block:: js
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// Create condition for Alice and Carly
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let subConditionFrom = driver.Transaction.makeEd25519Condition(alice.publicKey, false)
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let subConditionTo = driver.Transaction.makeEd25519Condition(carly.publicKey, false)
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// Create condition object with threshold and subconditions
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let condition = driver.Transaction.makeThresholdCondition(1, [subConditionFrom, subConditionTo])
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// Generate output with condition added
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let output = driver.Transaction.makeOutput(condition)
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// Add Carly to the output.public_keys field so she is the owner
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output.public_keys = [carly.publicKey]
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let transaction = driver.Transaction.makeTransferTransaction(
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[{ tx: txCreateAliceSimpleSigned, output_index: 0 }],
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[output],
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{'meta': 'Transfer to new user with conditions'}
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);
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// Add alice as previous owner
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transaction.inputs[0].owners_before = [alice.publicKey]
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// Because the addition of crypto conditions, the id for the transaction has to be regenerated
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delete transaction.id
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transaction.id = sha3.sha3_256
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.create()
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.update(driver.Transaction.serializeTransactionIntoCanonicalString(transaction))
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.hex()
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// Alice has to sign this transfer because she is still the owner of the created asset
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let signedCryptoConditionTx = driver.Transaction.signTransaction(transaction, alice.privateKey)
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As you can see, we need to generate a new transactionId because we have added crypto conditions.
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We do this with the js-sha3 package, you need to install this package through ``npm``:
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``npm install --save js-sha3``
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Don't forget to import the package in your code:
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.. code-block:: js
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import * as sha3 from 'js-sha3'
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If you would like to see a more complex example, please have a look [here](https://github.com/bigchaindb/project-jannowitz/blob/code-examples/js-examples/crypto-conditions.js)
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.. TODO: Document Utils when finished
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