Bitcoin would break with a compromised SHA256. If pre-image attacks on SHA256 become possible, one can replace transactions in the block chain with ones own tra

Bitcoin would break with a compromised SHA256. If pre-image attacks on SHA256 become possible, one can replace transactions in the block chain with ones own transactions. A SHA256 hash identifies each transaction, and if you can produce a transaction with the same hash, but one that pays to you instead, you can replace transactions in the block chain with ones that pay to you.