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Running BOLD Challenges on Sepolia

This guide will set you up to perform BOLD challenges on Ethereum Sepolia.

Sepolia endpoint (keep internal):

 export SEPOLIA_ENDPOINT=https://sepolia-geth.arbitrum.io/bold8c7987d041065bf04de03d19ba50

Honest validator priv key (keep internal):

 export HONEST=ee3c0bf39d962a78dba87aee083cae443cabc814f93677f302cbabde844237db

Evil validator priv key (keep internal):

 export EVIL=93690ac9d039285ed00f874a2694d951c1777ac3a165732f36ea773f16179a89

I recommend running your own Sepolia node. It is fast to sync and less error prone than using a external RPC.

Building the Testnode and Deploying Contracts

Ensure you have docker compose installed.

Clone https://github.com/OffchainLabs/nitro and checkout sepolia-tooling. Then git submodule update --init --recursive.

Next, navigate to nitro-testnode and modify the l1conn value in sepolia-bold.bash to https://sepolia-geth.arbitrum.io/bold8c7987d041065bf04de03d19ba50

Then, you can run the testnode setup to build the docker image and deploy the contracts to Sepolia:

./sepolia-bold.bash --init --dev --detach --no-tokenbridge --validate

After everything is setup, you should see something like this:

[+] Running 2/2
 ✔ Container nitro-testnode-poster-1     Running                                                                                                                                     0.0s
 ✔ Container nitro-testnode-sequencer-1  Running

You can then view the logs for your batch poster and sequencer with docker logs -f nitro-testnode-poster-1 and docker logs -f nitro-testnode-sequencer-1 to ensure they are operational.

Funding and Approving Validators' Stake Tokens

The next step is to fund two validators with stake tokens needed for participating in challenges. The deployment from the last step also deployed a stake token at an address.

As a first step, you'll need to extract the l2

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then click on nitro-testnode_config and find the l2_chain_info.json file:

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Copy it somewhere - you'll need it later. Within, find the rollup and stake-token addresses. Set them as env vars:

export ROLLUP_ADDR=...
export STAKE_TOKEN_ADDR=...

Next, in the Nitro repo, navigate to bold/ and run:

go run tools/fund-weth/main.go \
 -validator-priv-keys=$HONEST,$EVIL \
 -l1-endpoint=$SEPOLIA_ENDPOINT \
 -rollup-address=$ROLLUP_ADDR \
 -stake-token-address=$STAKE_TOKEN_ADDR

Send out Arbitrum Deposits

Next, send out some Arbitrum deposits of different values. Avoid sending 0.001 ETH deposits, as those will kick off a challenge. The evil validator is configured to intercept all deposits of 0.001 ETH.

Find the inbox address in the l2_chain_info.json and send out Arbitrum deposits via a tool such as metamask.

Send to the inbox address any value except for 0.001 ETH. Send it the hex data:

0x0f4d14e9000000000000000000000000000000000000000000000000000082f79cd90000

After 6-7 minutes, the batch poster will post a batch containing your deposits.

Run your Validator(s)

The validator docker compose files and configs are contained in a separate repo. Clone the repo:

git clone https://github.com/rauljordan/bold-validator-starter-kit && cd bold-validator-starter-kit

Copy your l2_chain_info.json file into both honest-validator and evil-validators folders.

Run your honest validator:

./validator.sh --private-key $HONEST --eth-rpc-endpoint $SEPOLIA_ENDPOINT

Run your evil validator in a separate window

./validator.sh --evil --private-key $HONEST --eth-rpc-endpoint $SEPOLIA_ENDPOINT

Send out a Deposit Value to Kick-Off a Challenge

Next, send out a deposit for 0.001 ETH using metamask to the inbox address. After 6-7 mins, a batch will be posted, and your validators will disagree. A challenge will then begin.

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A fundamental property of blockchains is the notion of "finality," which roughly means that after a certain period of time, transactions that have been included in the canonical chain are extremely difficult or almost impossible to revert. Eth2 has an "explicit" mechanism of chain finality enshrined within the protocol, which is different from the "probabilistic" finality found in proof-of-work chains such as Ethereum or Bitcoin today. In proof of work, consensus is fundamentally a global race that a lucky miner wins by being the first to produce a valid block: a result of finding a mathematical solution to a computationally difficult problem. As such, block times are probabilistic. The more blocks are added to the chain, the harder it is to revert, as each represents a cumulative sum of electrical and computational power required to create it. Given there are real, physical guarantees that would prevent an attacker from being able to revert the Bitcoin and Ethereum blockchains today, we can consider transactions past a certain amount of time included on-chain as "finalized." The objective of Stateless Ethereum RPC is to enable the client to operate without the need to store the entire state tree. Ethereum proof of stake, however, does not function on the concept of probabilistic finality. Instead, it enshrines finality into the protocol by saying "If > 2/3s of validators have voted correctly on the chain head for a long period of time, we can consider everything before a specific checkpoint as finalized". Finality is explicit, and nodes that follow the protocol will not be able to revert the finalized checkpoint as it is fundamentally impossible regardless of consensus weight. How Finality Works in ETH2 ETH2 is a synchronous protocol that operates on a "checkpoint" mechanism for bookkeeping. Essentially, a set of validators is assigned to either produce blocks or vote on blocks in a window of 32 potential slots. Each slot is a period of 12 seconds. Those 32 slots constitute an epoch. In an epoch, there are 32 assigned block proposers and everyone else is known as an attester, assigned to vote on proposed blocks once per epoch. There is only one block proposer assigned per slot, but many "attesters" can be assigned per slot For example, Alice is selected as a block proposer for slot 4 in the epoch and Bob, James, Charlie, and Susan are assigned as attesters at slot 4, meaning they should be voting on Alice's produced block as canonical.

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Contextual logging:

Dec 6, 2023
Generalized History Commitment

Today in BOLD, challenges can have subchallenges, and we have a total of 3 levels. We do this because at each challenge, validators have to commit to N state roots of a block’s history, which can be very expensive to compute. For example, computing 2048 machine hashes for the execution of a block and collecting them takes around 5 minutes on a modern MacBook Pro.

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If I Had a Reset Button...

If you knew what you know now, and you were starting a new CL from scratch, what structures would you use? Let me start myself to set the tone, you can make it language specific (for example Go and avoid templated methods) but I am not really interested in the small details but rather the main components of the critical parts of code. Typical questions I’m thinking about areWould you use a custom allocator for the beacon-state/validators/attestations structures?Would you use a struct like object for them or would you use a functional style object. The typical situation is this:We have a buffer with 8192 roots in the BeaconState, but these roots are sequential, if state for N had up to root r, the state for N+1 will share essentially all of the roots as that for N except at one point where it would have changed one. If you store vectors and then you want to share the common part then you are lead to structures like the multi-value slice or similar structures, where you have a base slice and then somewhere else you store the diffs (or some mathematically equivalent statement). Another way to store the object is as a linked list (with some additions to make it into a round buffer) and when you change one element you just change a single node on that list, someone that holds the pointer to the current node will resolve to the current full round buffer, while someone that holds the pointer to the previous-to-modified node, will resolve (by traversing the links from it) to the previous full round buffer. If you have a fork this still works, you just need to add a few pointers on either side of the fork. The point is that from the point of view of the structure itself, there’s no “base state” and some diffs, and rather you can just delete the pointer and let GC in Go, or the Destructuror in C++ deal with the rest. No need to be pruning yourself from a multi-value slice for example. On the other side, the multi-value slice would incur in way less memory fragmentation if you are dealing with a single state in the happy case.There are variations of this for all structures in the Beacon State and there are benefits and cons for each one of them.What sort of thread management would you use? (I think here there won’t be a disagreement and just relying on the Go runtime is fine)What sort of fork management would you use? I originally thought about templating, something like having the Fork being the template parameter for a BeaconBlock structure. In C++ at least, the best structure seems to be vertical polymorphism in the structures themselves like having class AltairBlock : public Phase0Block but not use methods of these structures, but rather pure functions like attestations(block Block) []Attestations and just let AltairBlock and Phase0Block satisfy the concept Block, which in this case would mean they both have a member attestations so you can just simply implement that function as return block.attestations. In Go this seems to be quite complicated, templates as far as I could read do not allow us to do this, and interfaces themselves we have them, but we still are forced to repeat the underlying structures completely for AltairBlock and Phase0Block instead of invisibly inheriting and obscuring the changed ones.Would you trade security and correctness for performance? I think this is a funny one: if you’re coding for 0.1% of the market, then you can do lots of shit like only keeping the last two states and break if there’s a depth 3 reorg. That’s an extreme case, but that’s probably not so far away from what Erigon’s CL may be, I would bet that they just follow blindly whatever is voted. But besides the extreme cases, how about Optimistic sync? I am pretty sure we are the only ones that considered a recursive system in which a bunch of branches turned out to be invalid. I am convinced that you can simplify a lot the optimistic status dealing if you just ignore correctness in a bunch of cases, with no real danger to the network.How would you deal with the engine? Would you change the interaction with the engine if you knew that ALL your users are using MEV-Boost? would you optimize the builder code in detriment of the local code? for example, it could be perfectly valid to not wait for local blocks and not request them in advance until it’s late in the block in case we know we are not resource-heavy. Not wait for the result of FCU is also good, since we are guaranteed already from a VALID response from NewPayload (this is something we could do right now on Prysm).

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