Do Bitcoin miners verify validity of merge-mined Namecoin blocks?


I've been reading a little about merged mining as used in Bitcoin and Namecoin.

It seems like merged mining effectively eliminated Namecoin-only mining pools, right? Since Namecoin-only pools are mostly 'out-mined' by the Bitcoin merged mining pools, it seems pointless to start one.

In this case, I had a concern about the incentives of Bitcoin merged-miners to verify Namecoin blocks (i.e. check Namecoin transactions, name updates, etc.). So my question is: Do Bitcoin merged-miners verify the Namecoin block before starting to mine on the merged block? I assume they do.

I suppose if they don't verify the Namecoin part, they save some computation-time but they stand to lose the Namecoin reward, which is not that high anyway. Is the saved computation time ever worth losing the Namecoin block reward?

Alin Tomescu

Posted 2016-04-04T22:33:39.993

Reputation: 1 207

Where do you think they get the block from? Generally, the only way to tell what block to build on top of is to verify it. – David Schwartz – 2016-04-05T02:00:11.850

I assume you mean the Namecoin block? I don't know who exactly advertises the Namecoin block to the Bitcoin miners. I am thinking that maybe instead of advertising the full block, just its hash is advertised. Or if the full block is advertised, the Bitcoin miners might want to save some cycles. So they might not verify the block content and just compute its hash, which they then incorporate into the Bitcoin block. That would be bad, and you're saying it doesn't happen. I suppose the Namecoin reward is always worth the time to verify the Namecoin block? – Alin Tomescu – 2016-04-05T17:25:04.040

They have no choice but to verify it. The way you get a Namecoin block is by verifying it. There isn't some service they use that provides them with unverified blocks. – David Schwartz – 2016-04-05T23:04:30.590

I would say they have another choice: to just hash the Namecoin block without verifying it (after putting in their private key for the block-reward) and incorporate the hash into the Bitcoin block. – Alin Tomescu – 2016-04-06T12:43:18.990

What is "the Namecoin block" that you are talking about? Are you suggesting that they have some service that provides them with unverified Namecoin blocks? Who do you think provides such a service and what purpose do you think it serves? How would a person get a Namecoin block to hash without verifying it? – David Schwartz – 2016-04-06T16:42:38.423

Here's how I think things work. Bitcoin miners are part of the Bitcoin P2P network and see all Bitcoin transactions. They use whichever transactions they want, verify them and build a Bitcoin block. To merge mine Namecoin, I suppose Bitcoin miners participate in the Namecoin P2P network as well (assuming there is a separate one). If they do, then they would get Namecoin transactions, verify them and assemble a Namecoin block (assuming they also store the Namecoin block-chain to verify those transactions against). Their incentive is to verify the Namecoin transactions for the Namecoin reward. – Alin Tomescu – 2016-04-07T23:52:42.437

Exactly. They have no way to get a Namecoin block other than by monitoring the network and verifying what they see. You seem to be assuming the default is to get the information and that verifying it is extra. But without access to some trusted source, verification is necessarily already part of the process of getting the information. – David Schwartz – 2016-04-08T00:51:50.477

Thank you David. I found a small discussion about the incentives of Bitcoin miners to verify Namecoin blocks in Princeton's recent draft book called "Bitcoin and Cryptocurrency Technologies" (see "Merge mining and security" on pg 278-279 here). They point out one scenario in which small Bitcoin miners might skimp out on Namecoin verification to save some costs. This was the type of attack that I was worried about.

– Alin Tomescu – 2016-04-11T16:52:54.347

Small miners skimp out on all verification, including Bitcoin verification. They just use a mining pool. – David Schwartz – 2016-04-11T18:38:41.337

A similar question was asked here, go through it, it should give an answer to your question.
A more detailed explanation is given on bitcoin wiki

– tbolt – 2016-12-20T15:57:18.790

No answers