이중 지불 (Double-Spending)
디지털 화폐를 중복해서 사용하는 위험.
Double-spending is the central problem that all digital currency systems must solve. Since digital information is infinitely reproducible, a user could theoretically 'copy and paste' a digital coin to spend it twice. Centralized systems solve this with a master ledger (bank). Decentralized systems like Bitcoin solve it using Consensus Mechanisms (Proof of Work) and a globally shared blockchain, where transactions are timestamped and verified by a network of nodes.
graph LR
Center["이중 지불 (Double-Spending)"]:::main
Pre_blockchain["blockchain"]:::pre --> Center
click Pre_blockchain "/terms/blockchain"
Pre_hashing["hashing"]:::pre --> Center
click Pre_hashing "/terms/hashing"
Pre_cryptography["cryptography"]:::pre --> Center
click Pre_cryptography "/terms/cryptography"
Rel_51_percent_attack["51-percent-attack"]:::related -.-> Center
click Rel_51_percent_attack "/terms/51-percent-attack"
Rel_consensus_algorithm["consensus-algorithm"]:::related -.-> Center
click Rel_consensus_algorithm "/terms/consensus-algorithm"
Rel_block_reorgs["block-reorgs"]:::related -.-> Center
click Rel_block_reorgs "/terms/block-reorgs"
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🧒 5살도 이해할 수 있게 설명
현실에서는 1,000원짜리 지폐를 친구에게 주면 내 손에는 남지 않아요. 하지만 디지털 파일은 복사하기 쉽죠. 블록체인은 내 장부에 있는 '디지털 1,000원'을 복사해서 두 사람에게 동시에 주는 속임수를 쓰지 못하도록 막아줍니다.
🤓 Expert Deep Dive
The 'Byzantine Generals Problem' is the theoretical root of double-spending prevention. Bitcoin's Nakamoto Consensus used PoW to create a relative time-ordering of transactions. If a user tries to spend the same UTXO (Unspent Transaction Output) in two different blocks, the network only accepts the first one validated. 51% Attacks are essentially attempts to manually induce double-spending by rewriting the blockchain's history.