Tony Giorgio [ARCHIVE] on Nostr: 📅 Original date posted:2022-06-07 📝 Original message: Hi, For the past few ...

📅 Original date posted:2022-06-07
📝 Original message:
Hi,

For the past few months I have been working on an LDK probing project that searches for unannounced channels on the Lightning Network. For the past week, I have been probing on mainnet and squashing bugs / making optimizations.

So far I have found near 445 unannounced channels totaling 1,076,077,750 satoshi's locked across the 3 nodes I have probed, some with just a minimized set (~30,000) of probable channels based on "round payment amount" and "1 or 2 tx output" heuristics on P2WSH UTXO's. Most of them being on Aincq's node found with the minimized set, I've yet to run the complete set with them. There are about ~860,000 P2WSH UTXO's, about ~60,000 of which are public, so the upward limit of possible private channels is around ~800,000.

The exact results are publicized here: https://github.com/BitcoinDevShop/hidden-lightning-network/blob/master/data/results/results.json

The reason this is possible is because probing is a free operation on the Lightning Network after a channel is opened, the error reasons given are way too verbose, and currently channel IDs are based on UTXO's. Scid aliases may be the biggest benefit here, but the use of `unknown_next_peer` , `invalid_onion_hmac`, `incorrect_cltv_expiry`, and `amount_below_minimum` have been the biggest helpers in exploiting channel privacy.

By creating a probe guessing the Channel ID based on unspent p2wsh transactions, it's a `m * n` problem to probe the entire network, where `m` is utxos and `n` is nodes. Without these errors and instead something like `temporary_channel_failure` or a generic indistinguishable error, guessing a Channel ID would come down to an upwards of `m * n * n-1 * ~2000`, which would be each utxo with each pairing of nodes, each with about ~2000 cltv's to guess (numbers are as low as 7 to as high as ~2000). I threw the extra 2000 into the equation because even with `800,000 * 1 * 2000`, it gets much more time consuming to even probe a single node when we're already spending upwards of a day or so for near 1 million or 2 probes. Concurrent probing is possible, but starts to require more locked up liquidity.

We should definitely migrate to alias scid's, and encourage every active unannounced channel holder to close, coinjoin, and reopen with an alias. But care should be given in the future when it comes to error reasons revealing information that is meant to be "private". Until this migration happens, it would be beneficial to stop being so specific about errors, this does not really seem to help end users anyways.

I'll be continuing with this probing project while the problem exists, and work on narrowing down the other channel partner and fixing efficiency bugs. I am publicizing the results as I go, so fair warning that if you have any unannounced channels that you assumed were private and need them to be, close them now on the off chance they get revealed. This could have always been happening already already by analytic firms, so I hope by publicizing this we are all on the same playing field. It is also beneficial to get a better estimate of the unknown size of the Lightning Network.

For more about this project and viewing the dataset, go to http://hiddenlightningnetwork.com

Thanks,
Tony
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