Dexie Incentives Program and the Case of the Very Expensive Offer File

This article was adapted with permission from a Twitter thread by @endertown. See the original thread for further discussions.

Time for another caper! If you missed the first case, you can catch up here: Dexie Incentives Program and the Case of the Auto-Canceling Offer File

The healthy fee market continues to reveal fun little gotchas that didn’t come up when there was no need to worry about fees, and this case is no different.

As we discussed in the first case, an offer file is just a list of real, specific coins from your wallet that you are offering in exchange for a list of other coins that you are requesting.

Did you know that the minimum fee required to accept an offer file depends on how many coins are in those lists? This means that two offer files could offer and request the exact same values, but if one is just offering a single coin and the other is offering 100 coins, the simpler single-coin offer will be much cheaper to accept in minimum fees!

So, recall from our first conversation that what we really want (as the bad guy) is to put up offers that are never accepted. This way we just sit back and collect DBX incentives.

Well – we just found a way to make offers really expensive. 👀

As a test, I created a minimum offer file for a little over 11,000 SBX but I used 99 coins in the offer file instead of a single 11,000 SBX coin. You can see it here:

Partial list of Dexie’s visualization of input coins in the offer file.

Look at all those input coins!

I was able to finally accept it myself with a 0.02 XCH (!!!) fee after trying lots of smaller amounts. A normal user would have probably given up long before getting to that fee amount.

As the bad guy, we’d just generate thousands of these minimum offers with 99 coins each and sit back and collect those sweet incentives while nobody wants to accept these high-fee offers!

Dexie has already tightened up this little loophole as well. They now only accept up to a maximum of 25 coins for incentivized offers instead of 100. They also continue to add features so that users can easily see estimated fees before they accept the offer.

Remember, you can always “Inspect” any offer file on Dexie to see the input coin list. This will give you a feel for the “weight” of the offer relative to a simple offer that just offers a single coin.

Thanks again to the folks at Dexie for a quick response and fix!

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Josh Painter
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