It's more of a tree with single root and a function returning the longest tip by some distance method. Bitcoin uses amount of work proved as the distance. Bitcoin ignores other tips unless/until one of them becomes longer than the current tip but some systems like Ethereum leverage stagnant branches for their length function.

But yes, dynamic-membership multi-party signature schemes and their use for creating permissionless systems is the real innovation.

Straight question for the uninformed (me):

Do you (or anyone else) have a technical reference for differences between the Bitcoin and Ethereum blockchain length function?

Bitcoin's method is detailed in Satoshi's classic paper:

https://bitcoin.org/bitcoin.pdf

Ethereum uses a variant of the GHOST algorithm, which was introduced in the paper Accelerating Bitcoin’s Transaction Processing: Fast Money Grows on Trees, Not Chains.

https://eprint.iacr.org/2013/881.pdf

The Ethereum white paper mentions how they modified it:

https://github.com/ethereum/wiki/wiki/White-Paper#modified-g...

Full detail is in their infamously difficult Yellow Paper:

https://github.com/ethereum/yellowpaper

Thank you for all those links!

I had some idea about the Bitcoin blockchain - also succinctly summarized by @tylerswift.

But the Ethereum material is all new to me. It at least sounds more interesting than "the least interesting".

There's a bit more to it. Proof of work hashing and ledger consensus rules and difficulty targets and fee schedules and forks.

It's still all standard bachelor's degree algorithms, and I agree with the gp that it's not the interesting part. The interesting part is using these algorithms for social consensus on value.

I disagree those are essential. Federated chains like Elements Alpha are also considered block chains but lack many of those properties. I think it really is the case that a "block chain" is merely a singly linked list with hash linkages.

But that's just an hash chain, it has existed for longer than the blockchain. For example, all digital invoices in my country are hash-chained, to prevent the merchant from swapping one for another, and this standard was published before Bitcoin.

I don't disagree with anything you said. Even generously most of the "blockchain" hype is an excuse for cryptography that has already existed without application for some time.

That sounds interesting. What is the standard called? I'd love to read more about it.

SAF-T: https://en.wikipedia.org/wiki/SAF-T

It's not that special, each invoice gets assigned as hash of (invoice number + total amount + date of emission + hash of previous invoice). Besides having to send that XML file to the IRS each month with all the issued invoices, the hash also gets printed on the invoice given to the client (paper or PDF), so it gets tricky to change the past without getting caught.

This. Seriously I was talking to a neighbor just the other day about how the most interesting aspect is the application!