# Erasing Data from Blockchain Nodes

## TL;DR

This paper introduces a practical method called functionality-preserving local erasure (FPLE) that allows full blockchain nodes to erase specific data locally while still maintaining network participation and validation capabilities.

## Contribution

It proposes and demonstrates a novel FPLE approach enabling nodes to erase undesirable data without losing full validation functionality in UTXO-based blockchains.

## Key findings

- Nodes can safely erase transaction data and still validate blocks.
- The proof-of-concept tool effectively complies with more erasure requests than existing methods.
- Full nodes remain operational and synchronized after data erasure.

## Abstract

It is a common narrative that blockchains are immutable and so it is technically impossible to erase data stored on them. For legal and ethical reasons, however, individuals and organizations might be compelled to erase locally stored data, be it encoded on a blockchain or not. The common assumption for blockchain networks like Bitcoin is that forcing nodes to erase data contained on the blockchain is equal to permanently restricting them from participating in the system in a full-node role. Challenging this belief, in this paper, we propose and demonstrate a pragmatic approach towards functionality-preserving local erasure (FPLE). FPLE enables full nodes to erase infringing or undesirable data while continuing to store and validate most of the blockchain. We describe a general FPLE approach for UTXO-based (i.e., Bitcoin-like) cryptocurrencies and present a lightweight proof-of-concept tool for safely erasing transaction data from the local storage of Bitcoin Core nodes. Erasing nodes continue to operate in tune with the network even when erased transaction outputs become relevant for validating subsequent blocks. Using only our basic proof-of-concept implementation, we are already able to safely comply with a significantly larger range of erasure requests than, to the best of our knowledge, any other full node operator so far.