詳細看這個：
http://bitcoinmagazine.com/6021/bitcoin-is-not-quantum-safe-and-how-we-can-fix/這裡有你們所有想知道的！
這是公鑰被
真量子計算機破解所需時間等級：
Shor’s algorithm reduces the runtime of cracking elliptic curve cryptography from O(2^k/2) to O(k^3) – that is to say, since Bitcoin private keys are 256 bits long, the number of computational steps needed to crack them goes down from 340 trillion trillion trillion to a few hundred million at most.
就算地址沒花過錢也不安全，危險就在花錢的那一刻，當交易開始廣播的時候，交易可能被不誠實礦工攔截，直接把私鑰破解，然後就呵呵
If you send a transaction spending all 100 BTC in address 13ign, with 10 BTC going to 1v1tal to pay for goods and 90 BTC change going back to your new address at 1mcqmmnx, the first node that you send the transaction to can replace the change address with whatever they want, recover the private key from your public key, and forge your signature. The only way to get around the problem is essentially to send the transaction directly to a mining pool, like BTCGuild or Slush, and hope that the mining pool will be honest and place the transaction directly into the blockchain. Even then, however, you are vulnerable to a Finney attack – a dishonest miner can forge your signature, create a valid block containing his forged transaction continuing the blockchain from one before the most recent block (the one containing your transaction), and, since the lengths of the old and new blockchains would then be equal, the attacker would have a 50% chance of his block taking precedence. Thus, safe transactions are essentially impossible.
