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I am writing a hardened Bitcoin node guide and I don’t fully understand the implications of pruning.

My understanding is that when one has a full copy of the blockchain, the node itself doesn’t reveal much about one’s UTXOs given everyone’s transactions are stored on the node (I believe same applies when using electrs).

Does pruning change something from a privacy perspective?

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  • Actually, electrs doesn’t support pruning, but still curious about privacy implications of pruning.
    – sunknudsen
    Feb 18 at 19:34

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No. The privacy benefit is not because there is a local copy of the full blockchain but rather because full nodes receive and verify all blocks and transactions. This allows full nodes to determine what transactions belong to any wallets it is managing without having to ask anyone else for those transactions specifically. They receive everything, and so can filter what is needed from there. Whether that data is stored does not matter. The relevant transactions are stored in their respective wallets.

Pruning just affects how blocks are stored on disk. It is a node operation detail and not related to the wallet. Nodes with pruning enabled still receive and verify all blocks and transactions, and so any wallets being managed by the node will learn of their transactions. Blocks are still written to the disk - they just end up getting deleted eventually rather than staying permanently.

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  • Thanks for helping out… what if someone has access to data on node… can person determine which addresses are monitored by wallet such as Electrum? My understanding is that if node is not pruned, this is not possible.
    – sunknudsen
    Feb 18 at 20:32
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    @sunknudsen You seem to be under the impression that pruning only removes things unrelated to the wallet. That is not correct. It removes all old blocks, regardless of whether they are relevant to the wallet or not. The wallet keeps its own copy of transactions that are relevant to it, unrelated to whether pruning is enabled or not. Feb 18 at 20:52
  • @PieterWuille Naive question… if node is pruned, one cannot sync an Electrum wallet that relates to pruned blocks right? What happens if one tries to?
    – sunknudsen
    Feb 18 at 21:13
  • Electrum nodes need an Electrum server, not a node. It's up to that server what it indexes or not, and unrelated to whether the node(s) it fetches its data from prune or not, Feb 18 at 21:15
  • @PieterWuille Asking in the context of one running Bitcoin Core and electrs on same machine. Guess answer is one simply cannot enable pruning as implied here.
    – sunknudsen
    Feb 18 at 21:19

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