[quickthrower2]

"select * from transactions" won't tell you that this has happened.

But your blockchain client will know immediately if the single miner has rewritten the block chain. It won't be able to download any new blocks based on the one it current thinks is head.

So while you can't stop the miner from doing what you said, no one will be fooled when it happens.

[icebraining]

As I wrote in the reply to the sibling post, chain-signing the transactions is basic, just a few lines of code using a crypto library like NaCl. We did that for an invoicing API, it was one of the easiest parts, literally less than 10 lines.