SHA-256 Explained
📖 5 min read
Quick Answer
SHA-256 is the cryptographic "fingerprint machine" at the heart of Bitcoin. Feed it any data and it returns a fixed 64-character code that is unique to that data, impossible to reverse, and changes completely if you alter even one letter.
💡 Think of it as…
攪拌機可將任何餐點變成獨特的冰沙。你永遠無法從冰沙中重建出原來的成分——但如果有人遞給你同樣的飯菜，你總是會得到完全相同的冰沙。這種單向、可重複的屬性使得雜湊變得有用。
What a hash actually is
雜湊函數接受任何輸入——一個單字、一個檔案、整個區塊——並輸出一個固定長度的字串。無論輸入是一個字母還是一千兆位元組，SHA-256 始終輸出 256 位元（64 個十六進位字元）。
Three properties that matter
It is deterministic (same input → same output), one-way (you cannot work backwards to the input), and collision-resistant (it is practically impossible to find two inputs with the same output). The tiniest change to the input produces a totally different hash.
比特幣如何使用它
哈希將區塊連接在一起，將交易壓縮到 Merkle 樹中，並定義挖掘難題：礦工競相尋找哈希以足夠的零開頭的區塊。因為你無法預測哈希值，所以獲勝的唯一方法就是嘗試數萬億次——這就是工作量證明。
🔑 Key takeaway
SHA-256 turns any data into a unique, irreversible fingerprint. It is the glue that links the blockchain and the puzzle that miners must solve.
Why this matters for you
You never touch SHA-256 directly, but it is what makes the Bitcoin you buy on Coins.ph, Upbit or Tokocrypto impossible to counterfeit. It is the math that lets strangers across borders trust the same ledger.
常见问题
SHA-256 可以逆向或破解嗎？▼
No practical method exists to reverse it or find collisions. It would take longer than the age of the universe with today’s computers, which is why it is trusted to secure trillions of dollars.
Will quantum computers break SHA-256?▼
像 SHA-256 這樣的雜湊函數被認為相對具有量子抗性；更大的長期問題是公鑰簽章。如果需要，比特幣社群可以透過提案（BIP）升級加密技術。
Is SHA-256 used outside Bitcoin?▼
Yes — it secures HTTPS websites, software updates, password storage and more. Bitcoin simply put it at the center of a money system.