Bitcoin Whitepaper Exercises - Transactions

Similar to the previous Hashing exercise, in this exercise you will add the 8 lines of text from the provided poem to a blockchain. But this time, you will add each one as a separate transaction, authorize the transaction with a key and signature, and then add all 8 transactions to a single block. Finally, you'll validate the blockchain, including all the transaction signatures.

Setup

Run npm install in this exercise folder to install the dependencies listed in the included package.json file.

Run node generate-keys.js from the command-line to create the keys/ sub-directory which includes a keypair to use for digital signatures.

Part 1

Define a createTransaction(..) function that takes the text (line of a poem) and creates a transaction object. The transaction object should have a data. The transaction then needs a hash field with the value returned from transactionHash(..).

Define an asynchronous authorizeTransaction(..) function which then adds to the transaction object, a pubKey field with the public key text (PUB_KEY_TEXT), and a signature field with the signature created by awaiting a call to createSignature(..).

In addPoem(), for each line of the poem, create and authorize a transaction object and store it in the transactions array. Then add set those transactions as the data for a new block, and insert the block into the blockchain.

Part 2

Modify verifyBlock(..) to validate all the transactions in the data of a block. It may be useful to define a verifyTransaction(..) function.

Each transaction should be verified according to:

• hash should match what's computed with transactionHash(..)

• should include pubKey string and signature string fields

• the signature should verify correctly with verifySignature(..)

Print out verification that the blockchain is valid after having added all the poem text as transactions.