Sure it’s doable in precept: they might nonetheless serve historyless wallets, in trustless or trusted mode. The node would solely present UTXOs to the pockets, and SPV proofs for transactions that created the UTXOs.
Whitepaper Pruning
The Bitcoin whitepaper described the structure in “7. Reclaiming Disk House”.
As soon as the most recent transaction in a coin is buried beneath sufficient blocks, the spent transactions earlier than it may be discarded to save lots of disk area. To facilitate this with out breaking the block’s hash, transactions are hashed in a Merkle Tree [7][2][5], with solely the basis included within the block’s hash. Previous blocks can then be compacted by stubbing off branches of the tree. The inside hashes don’t have to be saved.
Reclaiming disk area
A block header with no transactions could be about 80 bytes. If we suppose blocks are generated each 10 minutes, 80 bytes * 6 * 24 * 365 = 4.2MB per 12 months. With pc programs sometimes promoting with 2GB of RAM as of 2008, and Moore’s Regulation predicting present progress of 1.2GB per 12 months, storage shouldn’t be an issue even when the block headers should be stored in reminiscence.
A node that might do that would hold:
- Header chain
- UTXO state
- Supply transactions of every present UTXO
- Merkle tree nodes wanted to have the ability to assemble Merkle proofs for UTXOs
Such node may nonetheless trustlessly serve historyless SPV wallets, with the caveat that they will lie by omission (hiding UTXOs that exist), or lie about spent standing (server gives an current spent TXO and claims it’s unspent).
Bitcoin Core Pruning
The above was by no means applied in Satoshi-era Bitcoin node, or later Bitcoin Core nodes. As an alternative, pruning is finished by merely deleting complete outdated blocks, and retaining solely the header chain and UTXO state.
Such nodes can validate transactions domestically however don’t function backends for mild wallets: they lack each Merkle proofs and UTXO indexing by tackle. UTXO indexing may very well be added, however with out SPV proof era, this is able to be a trusted structure: the server may fabricate non-existent UTXOs (which the shopper would solely uncover when making an attempt to spend) or misrepresent their content material.
