Surrogate Database Key, Not Bitcoin Protocol Flaw, To Blame For Mt Gox Problems

An anonymous reader writes "Bitcoin values dropped sharply over the weekend after the largest trading exchange, MtGox, revealed that an investigation into unusual trading activity turned up a flaw in the underlying Bitcoin software that allowed an attacker to double withdrawal a transaction" Not so fast according to database experts: the real problem is that Mt Gox (and other exchanges) are using a surrogate transaction id rather than a natural key in their databases: "The flaw isn't so much in Bitcoin as it is in exchange-systems. Many exchanges use the tx-id to uniquely identify transactions, but as it turns out, an attacker can change the tx-id without changing the actual transaction, rebroadcast the changed transaction (effectively creating a double-spend) and if his altered transaction gets accepted into a block instead of the legit transaction, the attacker receives his coins and can complain with the exchange that he didn't. The exchange will then check their db, fetch the tx-id from it, look it up in the blockchain and not find it. So they could conclude that the transaction indeed failed and credit the account with the coins. ... A simple workaround is to not use the tx-id to identify transactions on the exchange side, but the (amount, address, timestamp) instead."

Read more of this story at Slashdot.









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