The fun bit is that the signer can backdoor transactions, and that part isn't something that can be verified by anybody who doesn't have the private keys.
Can you explain this? This is contrary to my knowledge of reviewing the details of a pre-signed transaction.
This is only detectable if you have multiple signers signing the same transaction using the same private key and the same method for generating the nonce, and you compare them before broadcasting. So perhaps using hardware wallets from 3 manufacturers which all implement bit-identical implementations of the signer (with RFC6070 deterministic signatures), and treating the signed transaction as a private key leak until you've verified they all match.
For ECDSA a single bit bias in the nonce, or a single bit leakage of the nonce through other methods is enough to completely break the cryptography. So we could have hardware wallets that produce otherwise impeccable transactions and signatures, but leak a bit of the nonce in the ordering of the outputs, the lock time, the sequence numbers, and that would still be enough to steal all of the funds.
This stuff is trickier to get right than most people imagine.
Regardless, whatever job you have where what you've said is a legitimate threat model sounds like the most interesting job in the space.
I just looked it up but I couldn't find anything saying as much... only that sparkpool kept it aside in case the owner comes forward?
>In short, the researchers claim that the hackers have gained access to an exchange’s funds. They are able to send money to certain whitelisted accounts that are marked as reliable in the exchange’s database to—but not to their own. So, they are sending the funds with excessively high transaction fees to sap the exchange’s accounts, and they’re demanding a ransom if it’s going to stop.
Thanks for the link!