From a bitcoin full node, we can prune the blockchain from 350GB to 7GB (as of 30thJune2021) by storing the latest UTXO set plus maybe 120 latest block (for possible orphaning or block reorganization). Can pruning be done for blockchain that involves confidential transactions (Liquid network) since there are range-proof and pedersen commitment?
One way of looking at validation (in Bitcoin, and related systems) is to see the UTXO set as the primary data set a node operates on. Blocks are simply "patches" to the UTXO set, saying what entries can be deleted from it, and which new ones to create. Of course, blocks are more than that; they are also authenticated - they carry data with them to prove that said patches were legitimate.
Pruning is simply the practice of forgetting the patches after they've been applied. The patches can be forgotten, because they are not needed for future validation. Everything the node will need in the future is in the UTXO set.
In Bitcoin, the UTXO set contains entries of the form (
vout_index identity which transaction and which output of that transaction created the UTXO. The
amount is the number of satoshis the UTXO is worth, and the
scriptPubKey controls who has the ability to spend it. Transactions (and blocks) in addition also contain a
locktime, and transaction inputs (each with various fields, including signatures in
witness). None of these things make it into the UTXO set precisely because they don't matter in the future; they're only relevant for determining whether the transaction/block (patch) is valid at the time it is applied.
What changes in Confidential Transactions? The
amount is replaced with a Pedersen commitment, both in transactions themselves and in the UTXO set. So this is indeed kept for future validation (it's in the UTXO set, so it is not removed by pruning blocks). Transaction outputs in CT also have a
range_proof. What about that? Its function is to guarantee that the sum of the (hidden) transaction output values does not exceed that of the UTXOs being spent. Similar to signatures, this data is only needed at validation time. Once applied, it can be forgotten. Thus, it is not included in the UTXO set, and unavailable after pruning.