Re: Contrary to Mt.Gox’s Statement, Bitcoin is not at fault

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To clarify further: in an transaction, only the inputs, the outputs and the amount are signed. The TXID is -not- signed, and thus can be changed by anybody while keeping the transaction valid. It is -not- a bug, it's a design choice. The Bitcoin protocol never stated that the TXID was to be unchangeable, and thus nobody should have expected that in their software.

One can uniquely track transactions otherwise. Even if the TXID is changes, the inputs are not. Thus one can know if a transaction went trough by checking if a given input has been spent according to the blockchain.

Why not sign the entire transaction including the TXID?

Sign it with which private key? A tx can (and usually does) have multiple inputs.

Any random one? Even with thousands of inputs an attacker wouldn't be able to sign a mutated ID with any of the inputs.

Looking around I actually get the feeling that one of the reasons why this minor issue was left on the shelf was because there's so many different people with so many possible different solutions.