22kB-Sized Blockchain — A Technical Reference

In other networks, like Bitcoin or Ethereum, miners require the entire history of the transactions in the network (organized via the chain of blocks) to fully validate any portion of the current state of those networks. This is true for both account or UTXO-based networks. Any new node (or a node that was offline for a long period) will have to sync to the network trustlessly by downloading all the blocks they missed.

In other networks, like Bitcoin or Ethereum, there is a notion of a “light client”. These light clients are intended for low-capacity environments and help users to verify/access information relevant to them from the latest state of the blockchain without having to do an expensive (both in time and space) syncing operation. They do so by reading the header from a block and verifying that the balance is correct w.r.t to the block they received, thereby trusting that the full node that sends them the data. These light nodes are not capable of representing the “blockchain” as we’ve defined it above.

Mina replaces the entire blockchain, starting from genesis to any block, with an easily verifiable constant-sized cryptographic proof. Verifying this proof corresponding to a block amounts to verifying all the transactions up until a few blocks behind the current block. The proof and inputs to the verification function are all in the latest block that gets gossiped. Note that due to the definition of “blockchain” above includes the term “usable”. This definition means in succinct protocol like Mina, we need more than just a proof object coupled with a state full of opaque hashes.

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