Bitcoin Forum

I didn't see anyone discuss about it in this forum, but last week Jameson Lopp decide to attack testnet3 network to prove a vulnerability[1]. If you either attempt to use testnet3 recently or follow the news, you probably know it's not easy to obtain testnet3 coins these days. On top of that, recent Runes hype makes some people decide to add arbitrary data to testnet3 blockchain[3]. With some developer discussing new testnet network (not Signet)[4], i wonder how long will testnet3 remain usable and supported.

[1] https://beincrypto.com/jameson-lopp-bitcoin-testnet-griefing-attack/ (https://beincrypto.com/jameson-lopp-bitcoin-testnet-griefing-attack/)
[2] https://blockchair.com/bitcoin/testnet/ (https://blockchair.com/bitcoin/testnet/)
[3] https://protos.com/halving-excitement-pumps-worthless-bitcoin-testnet/ (https://protos.com/halving-excitement-pumps-worthless-bitcoin-testnet/)
[4] https://groups.google.com/g/bitcoindev/c/9bL00vRj7OU (https://groups.google.com/g/bitcoindev/c/9bL00vRj7OU)

Sharing his tweets about the attack

https://twitter.com/lopp/status/1781276372729524640
https://twitter.com/lopp/status/1780548492219318402

I discovered this website where this guy is claiming that users get rewarded with airdrops when using testnet, other sell testnet coins in swap services... so some users/dev are unsatisfied and are trying to get it down or change it.

There are still faucets dispensing testnet coins - I donated a small portion of my stockpile to one of the newer ones that was launched here a year or two ago.

I note also that they are being traded - that was only a matter of time.  Now, it looks as though people want to block those trades by resetting the testnet itself (which could cause consensus issues down the track)...

There has always been faucets giving coins and the only complains I've seen so far have been from people who want large amounts and the worst part is that I have not seen any reasonable arguments for needing such amounts as opposed to using something like regtest.
So I wouldn't say "it is not easy to obtain testnet coins".

What the future holds?
This attack is not going to change anything, after all this is not the first time testnet is under a miners' attack.
But if the trades continue and testnet coins start gaining a value and scams form around it, we can see testnet3 having the same fate as its predecessors and we may enter testnet4 era.
Although if we do, I think we should come up with better mining rules that are not complicated like signet and not as vulnerable like testnet3.

It is absolutely impossible to test anything on testnet as long as the coins have a value. Testnet coins are supposed to be worthless in order to deter people from swiping them from automated testing processed. Or in the event that they do get swiped, it's supposed to be easy to replenish them with more coins obtained from somewhere else. The fact that testnet coins are so scarce means that you can't even rely on that anymore, and if you want to test stuff then you need to simulate your own blockchain with a few (~3-5) blocks.

You don't need a lot of testnet coins to test stuff but you do need enough to cover the fees for long enough that the tests can run for several thousand iterations. So we are looking at around 0.1 to 1 tBTC for each project.

True. The big question is: what should be the new consensus rules of testnet4?

Because the story is that developers already tried to make a better version of the testnet, and they came up with signet. Which means, that in 2020, nobody had any good idea, how to make a good test network, without creating a permissioned network, where only creators could mine new blocks.

I know it is not about signet, but about testnet4, but I guess those two networks will be very similar. In general, if nobody has any good idea, then the status quo is what happens. Which means, that if nobody will invent anything better, then testnet4 will be the same as testnet3, but with a different Genesis Block, and without blockstorms. So, basically, it will be just like signet, but with signet challenge set to OP_TRUE.

This is not a bug, it is a feature. In case of the network reset, we may lose one important property: having a chain with a lot of halvings. And this is a problem, because the amount of test coins is what directly represents your ability of publicly sharing your tests. Which means, that if you have 50 tBTC, then you can push 5 GB of test cases. So, the amount of test coins is not something, that should correspond to the real values, used in mainnet. It is mainly about anti-spam features, and preventing people from flooding the network with their data.

This is the reason, why I agree with Garlo Nicon, that the new testnet should preserve existing halvings. So, even if all existing coins will be burned, then the block reward should not start from 50 tBTC, but rather from 0.01220703 tBTC, which we have today. Because the amount of coins you have, is what decides about your ability to push data. Which means, that if testnet4 will start from 50 tBTC, then each and every miner will get an ability to push 5 GB of data, and the new network will be flooded with data pushes from the day one, instead of being used to test payments.

This can be rectified by creating a new halfchain which is like testnet but the halving block lengths are significantly lower.

Maybe even signet can be adapted for this so that a new chain doesn't have to be created, but I don't know if that is possible or if it would require a new chain entirely. That being said, the Bitcoin Core team is not too thrilled about the prospect of modifying the current chains.

You can always claim less coins in the coinbase transaction, than you are allowed to. It is a perfect no-fork, not even a soft-fork. If you can claim 0.01220703 tBTC today, then it is the upper amount. You can as well always claim zero coins in the coinbase transaction, and your blocks will be perfectly valid in all networks: mainnet, signet, regtest, and testnet3.

Yes, but the situation is not so simple. If developers could simply pull off the plug, and destroy testnet3, by detaching it from the current client, then they would probably do so. But instead, they ask, if there should be any "grace period" or something, because they know, that people can simply stay with the old software. And in that case, testnet3 may become just another altcoin, probably much closer to the mainnet than many other altcoins.

And also, there is some risk of replaying coinbase transactions between networks. Which means, that if you have some block 1,234,567 in the current testnet3, then you can migrate exactly the same coinbase transaction into testnet4. And similar things can happen between signet and testnet4, or even mainnet and testnet4. One of the things, preventing that from happening, is the fact that testnet3 has much more blocks than other networks. Which means, that blocks from testnet3 can be copy-pasted into other networks, but not the other way around, because it would require a huge chain reorganization in testnet3.

I don't know whether any of you run testnet full node, but i just found out my testnet full node has total size 71GB.


I'm also surprised chainstate folder has size 7.8GB. So i decide to run gettxoutsetinfo and got following statistic which state there are currently 116.8 million UTXO.



You're right, but mining tBTC become more challenging. Not only due to lower reward, but also due to higher hashrate/difficulty[1]. And i notice there are less tBTC faucet these days. At least, it's not as easy as few years ago.

[1] https://mempool.space/testnet/graphs/mining/hashrate-difficulty#all (https://mempool.space/testnet/graphs/mining/hashrate-difficulty#all)

I think that is larger than even the bitcoin mainnet's chainstate, right? It was at 6GB or so the last time I checked its size.

But the fact that there is a ballooning UTXO set on testnet does not surprise me at all, as people rarely spend their coins after they are finish testing something. At best, they just return it to the faucet they got it from.

Mainnet's chainstate is still bigger at 11.3GB, with about 50% more total UTXO.


You might be right, but i recall chainstate/UTXO was far smaller a year ago. I need to dig the data for a while to prove that though.

I honestly never understood this and I've seen so many of those who ask for high amounts of tbtc say it. What are these tests that need to run "several thousands" times in a live network that can not be abstracted away using IoC design or something like that or even run in Regtest instead.

But coinbase tx is just a tx. There is nothing special about it in this context ("replaying" between networks). You set the version and the outputs of that tx and you get the same exact tx.

No you can't. Because the difficulty is different and also any block in any network is positioned inside a chain. You can't take out a single block from the middle of that chain and place it on top of another chain.
For example block 1,234,567 in Testnet3 is referencing block 1,234,566 on Testnet3 if you take that and try to place it on top of for example Mainnet chain at 1,234,567 it is rejected because the 1,234,566 reference is not found.
This chain also goes back all the way to a hardcoded Genesis block that is unique to that specific chain to prevent exactly what you explained.

https://bitcointalk.org/index.php?topic=5479988.msg63437260#msg63437260

As you can see, we have transaction ID 0f3601a5da2f516fa9d3f80c9bf6e530f1afb0c90da73e8f8ad0630c5483afe5 in the mainnet, and exactly the same thing is repeated in regtest. And in general, transactions can be migrated in such way, while preserving "the chain of signatures".

Of course, that "replay" is not "effortless". You have to mine a valid block header. But the problem (or the feature) is, that such transactions can be migrated. Which means, that even if someone will destroy testnet3, then exactly the same transactions, with exactly the same transaction IDs, can be replicated in testnet4, if there will be enough incentive to do that (and because some people started assigning value to testnet3 coins, then it may happen).

The only needed thing is to match the coinbase transaction. If that matches, then the whole chain of transactions is also matching. In general, if you recreate all UTXOs, used as inputs in a given transaction, then it can be replayed. Which also shows us, that if we want to replay something, then we have to trace that, only to the nearest coinbase transaction, because everything before that is just unsigned, and sent as fees, which can be taken from any transactions. The only requirement is to have matching amounts.

Of course, but note that the coinbase transaction does not contain the previous block hash. It contains only the number of the block. Which means, that such transactions can be replayed between unrelated networks.

Of course, but the chain of block headers is the only unique thing per network. The chain of transactions, and the chain of signatures, can always be replayed. For example: you send 50 BTC in the mainnet block 1,234,567 as fees, and you also send 50 tBTC in the testnet3 block as fees. And then, if you mine both blocks in both networks, then you can use the same coinbase transaction, with the same amount, and reach identical transaction IDs in both networks. And since then, you will have a connection, similar to the one existing between BTC and BCH, where you have a lot of shared history. But here, it goes further, because you don't have to start from the same point, to meet in the same transaction. Because if something is sent as fees, then starting transactions can be different in both networks, but the final outcome could lead to identical transaction data.

If you can replay transactions, then it means, that you can have two different chains, with two different histories, and they can end up with the same UTXO set. Or rather: a subset of their UTXO set can be identical in both. And the consequence is, that those coins will be connected, and if all of your transaction inputs are in that intersection, then they can exist in both networks. And the final consequence is "network migration", where you can set up the same UTXO set, and then just discard the original chain of block headers, and simply switch to the stronger one, because the whole set of data will be identical, so it will make no difference for the end user.

Also note that developers didn't get as huge hashrate in signet, as we have in testnet3. Which means, that if testnet4 will be almost the same as testnet3, then you will have a similar set of miners. And they may have a huge incentive, to just migrate the history, and get their tokens back in the new network. Which means, that a different set of rules is needed to prevent that, because if not, then you will have similar things in your mempool for testnet4, as you have in your mempool for testnet3.

I wonder, what do you think about using a subset of testnet3 for testing? I mean, you pick some kind of "challenge", similar to signet, and scan the whole chain of your choice (for example testnet3). And then, your UTXO set contains only a subset of the "real testnet3", matching that challenge. In that case, you can still test things, like in signet (for example if you pick your own signet challenge), but at the same time, you can import tests, provided by other people. And then, each node can have its own set of rules for accepting or rejecting transactions.

In that model, the network can be resetted at any time, by anyone, just by switching the challenge. But at the same time, you can pick and import any transactions at will, so if you will see anything interesting, that is done by someone else, then you can import it to your challenge, and get those UTXOs.

In general, I think such "Scanners" are worth exploring, because if you don't like something, that happens in testnet3, then it could also happen in testnet4, unless you will have some kind of "demurrage". And I think, that kind of "demurrage" is the most open for modifications, as it could be.

Testnet still has way more blocks. I didn't knew about that.

At time of posting, testnet is on block 2.800 million, while mainnet is still 800 thousands..

https://mempool.space/testnet/block/00000000000000cf5c1d4fda088f2623c34643c7677ffa6d71e0b3e62214d39b

This is due to the fact that the difficulty resets to 1 regularly on testnet.

Could anyone clarify this for me?  Why does testnet3 have halvings?  Given that the coins hold no value, there seems to be no rationale for imposing a supply cap.  It might be better to maintain it at 50 tBTC per block indefinitely, ensuring everyone always has an equal opportunity to earn a sufficient amount.  With halvings, it's only a matter of time before the network resets due to the absence of block rewards.


That's correct.  Spamming on the mainnet is discouraged because... you're paying actual money.  In the testnet, you could execute a spam attack at no expense. 

Because it is as close to the mainnet, as possible. In the first version, even the Genesis Block was identical, so it was possible to literally overwrite the whole chain. Then, some small changes were introduced here and there, people switched to some new Genesis Block, and added the famous rule of resetting the difficulty, which caused blockstorms later.

Ideally, the test network would have all rules, identical to the mainnet, but where you could experiment with worthless coins. And the main challenge is: what set of rules are needed, to make coins worthless, and to not departure from the mainnet by too much?

In that case, how do you test halvings, if they would not be present in the test network? Not to mention, that if you have no halvings, then after block 420,000, the whole supply will reach exactly 21 million coins, which means, that there will be some potential, to trigger some rules from the Value Overflow Incident. Because that amount "21 million" is hard-coded in some places, and if you have bigger supply, then some tests may fail. And also, if you have too many coins, then if you have conversions between integers, and floating-point types, then your representation may not be exact, and you may lose some precision.

And if you have no halvings, then you can always get a lot of fresh coins to spam the network at will. Because the amount you use, is correlated with the amount of data, which you can publicly share.

It's quite some months ago that I last ran a Core Testnet3 full node synced on one of my virtual machines. I remember some numbers like in the ballpark around 30GB for blocks, chainstate and indexes. Frankly, I'm shocked to see the current size easily doubled and more (can't remember from when my low numbers were).

And at the moment I also see blocks with nearly 4MWU size, insane! (OK, ok, if you want to test full blocks, they need to be filled to the limits.)

What's next? Inscribers abusing Testnet3 or other data spam dumped into the Testnet3 blockchain. WTF, this is pure madness!

The "can't" I said is the answer to this statement of yours:
You are saying "blocks" not a sequence of transactions that start from a duplicated coinbase tx. That threw me off the issue you are raising.

You are forgetting that the mess we are seeing is something that started recently and we are at block height 2.8 million. Only the coinbase tx of the same height can be duplicated, meaning you can NOT have coinbase of block #2.8 million as block #2 and create that "sequence" of UTXOs since the height is included inside the coinbase signature script.

If we migrate to version 4 (a brand new chain from block #1) and make the difficulty manipulation harder, it would take many years (50+) to get to block #2.8 million and by then nobody would even remember the said shittokens.

How about an annual replacement? Each testnet can last 2 years, so you don't have to change things during testing, but each year a new testnet starts so there's never a shortage in testnet coins. Testnet4 can start today, Testnet5 starts next year, and 2 years from now when Testnet6 starts, Testnet4 ends while Testnet5 still continues for another year.

I haven't used mine since January, and back then it was only 34 GB with 1.7 GB chainstate. Is that caused by Ordinal spam?

Altquick (https://altquick.com/exchange/market/BitcoinTestnet) uses FreeBitcoins.com (https://freebitcoins.com/faucet/) to provide a free faucet for those not needing whole coins or wanting to use the free market.

AltQuick doesn't determine prices... the market does, so if Bitcoin Testnet has zero value... the free market should reflect that.

It's the best way to run a faucet + keep coins circulating IMO.

We intend on listing v4 if needed.  *shrugs* No biggie... Testnet don't die, they multiple and it's our strongest market... (which is fucking insane).

I finally got the data of UTXO growth on testnet after enabling additional index and using command gettxoutsetinfo "none" block_height

Block height	Time	txouts value (total UTXO)
2415000	2023-01-06 17:41:19	28309184
2570000	2024-01-02 08:18:03	30140226
2588100	2024-04-19 17:32:26 (just before halving on mainnet network)	49671269
2810957	Today (when i write this post)	121751208

Since from beginning of this year, about 91M UTXO has been created. And since just before halving on mainnet network, about 72M UTXO has been created. So it disprove your speculation that it's caused by people who abandoned their tBTC after done with their testing.


Looking at above UTXO data and news i shared on this thread, it could be combination of Ordinal and Rune spam.

While new systems to these might be better than previous, there isn’t any certainty that they wouldn’t come with some vulnerabilities of their own.
Wouldn’t the more probable thing to do would be to improve on the existing system as per an improved version to it without coming up with an entirely different system all together?

I suppose the reasons for attacks and some of the hacking is often about discovering vulnerabilities or loopholes within a system and have it fixed. Rather than having to continue the same circle over and over again on new models or systems to these networks.

They should make their own version of Testnet: they can mine as much as they want, they can spam as much as they want, they can hype as much as they want, and they're not bothering the rest of us. Let's call it an altcoin. How ironic would that be, if Runes complete the cycle all the way back to the first thing created to get money from gullible people?

Testnet fees (https://live.blockcypher.com/btc-testnet/) are now higher than Bitcoin fees (https://mempool.space/). I'd say that's a win!

Shit is being tested... that much is for sure. :P

Win.


Testnet is already an altcoin.

#ThickSkinGang

The only thing weird here is that if you use the same tool to see fees on which network is higher, you get a different results.
Blockcypher reports higher fee on mainnet compared to testnet 0.00069 BTC/KB (https://live.blockcypher.com/btc/) vs 0.00032 BTC/KB (https://live.blockcypher.com/btc-testnet/)
mempool.space reports higher fee on testnet compared to mainnet 25 sat/vB (https://mempool.space/) vs 47 sat/vB (https://mempool.space/testnet)

Sometimes these fee estimators either have bugs or use different methodology that returns different fee estimation. I believe mempool.space is more accurate though.

It's like this with Bitcoin too for these estimator services.  Bitcoin Core's estimator is likely the worst offender.

All that matters is what their client can see.  (I've clearly had this bite me in the ass a few times on main net.)

We used to use our own wallet to estimate our fees, but for some reason couldn't see the whole network, now we use Mempool.

I thought Altquick was just a rebranding of freebitcoins? Or am I wrong about that?

We separated the exchange from the faucet.  The exchange rebranded to AltQuick.com and the faucet remained a faucet.

Brand issues for the products provided at the time.  ::) :D

People had a HUGE issue with "Free" + "Bitcoins" for a long time after the Twitter hack. 

I tested it in Electrum (testnet): it recommended almost 50 sat/vbyte, which puts it 0.66 MB from the top. When I tried 20 sat/vbyte, it got 130 MB from the top. With 10 sat/vbyte, I can't even broadcast it.
At least testnet has the difficulty adjustment thing, so once in a while it processes a lot of blocks to clear the backlog. But other than that, it's more congested than real Bitcoin.

I didn't get it in October 2023, when you wrote it, but it seems you were right:

https://www.ccn.com/news/crypto/bitcoin-testnet-could-need-reset-13-years-jameson-lopp-griefing/

@vjudeu: I wonder, if your next predictions from your topic will also be correct.

2.3 million pending unconfirmed transactions in v3.0 https://mempool.space/testnet (https://mempool.space/testnet)

Mempool and Lopp + some other dude on twitter say they launched a v4, but ehhh... it's not in core... it's just a shitcoin of a testnet coin IMO.  https://mempool.space/testnet4 (https://mempool.space/testnet4)

We shall see though I guess.

Testnet clearly needs some fixing, I think a v4 is a good idea, but done the right way and stuff fixed.

Huh? It is in Core: https://github.com/bitcoin/bitcoin/pull/29775

Judging by the current state of that discussion, I guess the Genesis Block will stay as it is now. Other blocks may change, but mainly people are discussing about network rules, like difficulty adjustments, so even if there will be some new Genesis Block, then it would contain just some block hash from the mainnet, and a zero-filled, completely invalid public key in the output.

Well, test coins are meant to be worthless. You can use this test network or another. It doesn't matter. You can also run signet with signetchallenge set to OP_TRUE, then you will get roughly the same outcome as testnet4.

So, what are the problems with testnet4, that you can currently see?

By the way: people can still use testnet3 if they want. This chain is decentralized. If it will be removed from Core, then it would mean, that it would simply turn into some kind of altcoin (just like testnet2 and testnet1 are now nothing more than some abandoned altcoins). And guess what: you can use an altcoin, even if there are no developers supporting it. But then, don't be surprised, if it would be completely unreliable, filled with blockstorms, and without any new bugfixes. And obviously, there would be constant attacks, to convince people, that they should switch into other test networks, where blockstorms are fixed.

Also, I guess new test networks will be resetted more often, which means, that we will get testnet5, testnet6, and so on in the next years. Which means, that if you want to test the network after many halvings, you will be forced to stay with testnet3, because no new test network will get there.

What kills V3 could kill V4, and i use the word kill because the V3 us unusable... a blockchain with 2.3M of unconfirmed transactions and blocks with only 67 transactions, that was a nice way to doom the network. An we should learn from it because if it happens in the test net it could happen in the main net too. I mean, isn't cheap but it's possible.

What would happen in altquick when the V4 comes? will it be a side market or you will drop V3 and only use V4?

It depends, what attack you have in mind. Because attacking testnet3 is possible, if you combine timewarp with blockstorms. But: there are some fixes in testnet4, so it won't be that easy to repeat it there. And of course, there are plans to fix timewarp in mainnet (but it is much harder to exploit it, because there is no "difficulty reset", and also it is not that easy to trigger it, so I guess the chain will be silently continued, without any splits, even if some fix will be applied).

Not that much. First, V4 is already there (and even if it will be resetted again, it seems that we reached a consensus, when it comes to the new Genesis Block). Second, there are many test networks, as well as many altcoins. It is impossible to support all of them, so it depends, which network will be picked by the users. And that network will be supported, while others may be simply ignored.

Test coins are worthless, so it is the same case if you switch from testnet3 into signet: you simply ignore your old coins, and get new ones from faucets (or mine them), and start accumulating your testing potential from scratch.

On top of that, i notice massive UTXO growth since 10 days ago.

• Block height 2810957 (about 10 days ago): 121751208
• Block height 2815079 (when i write this post): 144886406

If this continues, total UTXO on testnet3 will surpass mainnet within a month.

The same thing that happened to the market that existed on the second version of testnet where people traded those coins that led to the need for version 3. It dies.

I wonder how those people are getting all their testnet coins considering that only a few people appear to be mining it. They can't all be retrieving their coins from a faucet - that would most likely exhaust their supplies.

Have you seen trading volume or total amount of "asks" altquick? There's also other place to buy/sell tBTC which doesn't disclose it's volume or available supply.

Speculation on future value may be the reason why testnet4 is already plagued by ASIC miners: