key to control access to their bitcoins. Only those users who can generate valid signatures with their private keys can claim ownership for redeeming transaction outputs. Thus, a public key hash and a private key are essential to enable users to redeem funds. CONSENSUS, MINING, AND BLOCK VALIDATION In the absence of a trusted party, nodes follow a consensus on how to confirm or discard blocks and transactions so there are no conflicts at a later stage. This consensus in bitcoin is achieved by the concept of proof of work, which proves how much work has been put in to validate a block. A cryptographic puzzle is to be solved for the acceptance of any block and its addition to the shared ledger. This works by nodes accumulating the verified transactions in a block and applying their resources Transaction Identity (such as computation power and elecTransaction Owner tricity) to find a value that makes the UTXOs Address (Public Key SHA-256 hash value of this block less Hash) than a dynamically varying target Transaction Inputs value. The block contents include the Transaction Outputs arbitrary nonce, the hash of the previous block, the Merkle root hash of the Redeemed Transaction in Next Recipient Address Contents of listed transactions, the timestamp, and Transaction (Public Key Hash) Transaction the block version. The term proof of work refers to this random value that Owner Signature is found by the miners by repeatedly Transaction Verified Transaction TXNi hashing the block contents with many by All Network Broadcast to All Network Participants such random values to achieve the Participants cryptographic block hash. The blockchain structure is shown in Figure 5. FIGURE 4. The transaction broadcast and verification. Block Header Block Header Block Header Hash Value of Previous Block Hash Value of Previous Block Hash Value of Previous Block H H H Nonce Nonce Nonce Root of Hash Tree Root of Hash Tree Root of Hash Tree TX1-1 TX1-2 TX1-n TX2-1 TX2-2 TX2-n TX3-1 TX3-2 TX3-n Collection of Blocks HV H HV H Collection of Transactions HV H Coinbase T TX2-1 FIGURE 5. The structure of the blockchain. 10 IEEE Consumer Electronics Magazine ^ HV july 2018 HV HV H HV TX2-2 : Hash Value H : Hash Function HV TX2-n Transactions