Are transaction hashes predictable? - page 3.

dooglus

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Quote from: SgtSpike on November 11, 2011, 03:39:42 PM

Just curious... are transaction hashes predictable at all?

They're as predictable as any other hash. The algorithm used to generate the hash is known, so in that sense they're entirely predictable. But you have to run the hashing algorithm to 'predict' them.

It would be possible to put a confirmation step in the client before sending a transaction: "this transaction with have hash xxxxxx: [send] [cancel]. Since the coins used in a transaction are randomly selected by the client, you may well be able to get a hash beginning with the required byte if you have enough private keys with funds on them, and enough patience. Or the process could be automated.

piuk

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You would need to exclude coinbase transactions.

DeathAndTaxes

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Gerald Davis

Quote from: SgtSpike on November 11, 2011, 03:39:42 PM

Just curious... are transaction hashes predictable at all?

This is really a sub-question of a much broader question, which is, could the transaction hash be used to determine the winner of a lottery? In other words, if I said, the first person to send 1 BTC to this address, and gets a transaction hash beginning with 3f, is there any way a person could abuse it to where they only actually complete the transaction if the hash begins with that 3f?

The way you worded it is unclear. Who is abusing what? Why would someone only want the transaction if it begins with 3f?

If you are saying you are making a lottery and the winner is someone who sends 1 BTC and the hash begins with 3f then yes that is very exploitable.

You can't predict a hash but you can randomly attempt hashes from a pool of private keys until you find one which begins with 3f and then submit that one.

casascius

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The Casascius 1oz 10BTC Silver Round (w/ Gold B)

About the only abuse I could think of, is if someone solves a block and chooses to discard the block if they know it will cause the lottery outcome they don't want. They would get the equivalent of another roll of the dice by doing so.

BUt they would also forfeit the 50 BTC for solving the block. So that extra chance better be worth it. And only the lucky miner (or pool operator) who solved the block being used in the lottery would have the opportunity to abuse this.

SgtSpike

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Just curious... are transaction hashes predictable at all?

This is really a sub-question of a much broader question, which is, could the transaction hash be used to determine the winner of a lottery? In other words, if I said, the first person to send 1 BTC to this address, and gets a transaction hash beginning with 3f, is there any way a person could abuse it to where they only actually complete the transaction if the hash begins with that 3f?

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