I wrote my own ECDSA signature algorithm just for the purpose of creating unit tests.
With it I created two signatures which went into transaction 56ec7ca7df…, sending from 1GXFXm3es…. These signatures used the same k values, although k values must never be reused.
Later on, someone was able to steal 0.0016 btc from 1GXFXm3es…. and send them to 17WRjamox6VhTUaHsTWfFnMNDYHvwCtWio.
So someone must be monitoring the blockchain for mistakes like this and stealing funds if they encounter them.
How do you derive the private key from two signatures that share the same k value?
