Simple UTXO based Blockchain Exchange

V1

• In this version there is no transaction fee and block logic.
• Only includes account, transaction and the sequence logic
• The core logic is implemented in apps.blockchain.services which encapsulates the service layer of the system
• The blockchain logic is implemented at apps.blockchain.services.TxService inspiring UTXO-based blockchain systems like Bitcoin. Models:

TxOutput >- Transaction -<  TxInput
Account >- FiatTransaction -< Transaction

• Each Transaction can have multiple inputs and outputs.
• Every TxInput is checked to be signed by the user's private key
• Every FiatTransaction references one Transaction and one Account.

UTXO Flow

• On registration each user is given a key pair: private & public
• User submits signed a set of TxInput with their corresponding output.
• Then TxService verifies the signature with the public key of the UTXOs that the TxInputs reference using DigitalSigner (which in turn uses ECDSA algorithm)
• If it is valid then it generates the outputs and spend the referenced UTXOs
• Balance is calculated by summing up the values of UTXOs which user's account public key points to

Cash Flow

• Each user can buy crypto or sell them.
• Buy: A FiatTransaction is created which further gets verified by the payment gateway. On verification, a spend transaction happens on admin wallet that generates UTXO for the user public key. After that server marks fiat transaction as spent
• Sell: User submits a transaction that uses admin public key and the server transfers fiat to the user's bank account.
• Balance is calculated by summing up the values of unspent verified fiat transactions