TITLE: Redactable Blockchain or Rewriting History in Bitcoin and Friends

AUTHOR: 刘学枫 — CATEGORY: BLOCKBENCH —

Papers Link

Redactable Blockchain or Rewriting History in Bitcoin and Friends.pdf

Introduction

Category

• Problem Pattern: Less studied problem
• Idea Pattern: New FrameWork or Improvement

Motivation

Background

1. The immutability of blockchain fits perfectly with the currency system but not appropriate for all new applications that are being envisaged for the blockchain.
2. The ability to store arbitrary messages has already been abused that blockchain systems contain some improper content affecting the life of people forever.

3. Bitcoin 2.0 applications require re-writable storage.

4. 区块链的不可篡改性非常适合货币系统，但是却不是所有的应用都可以放到区块链上。
5. 区块链存储任意消息的能力被滥用，导致链上永久存储了一些会影响人们生活的垃圾消息。
6. 而且，比特币2.0的应用都需求可重写的存储模式。

Literature Review

• Bitcoin, the first prototype blockchain.
• Chameleon hash function.
• Anti-presistence: history independent data structure.

Research Niche

The immutability of blockchain fits perfectly with the currency system but not appropriate for all new applications that are being envisaged for the blockchain.

区块链的不可篡改性非常适合货币系统，但是却不是所有的应用都可以放到区块链上。

Work

Research Objectives

Propose a new design for redactable blockchain that integrated chameleon hash function and discuss some issues occurring in the redactable blockchain.

论文提出了一种整合了 Chameleon 哈希算法的新型可编辑区块链，并讨论了可编辑区块链的一些问题。

Insight

Chameleon hash function provide a trap-door that find collision-resistant efficiently. Thus integrating this function into blockchain can make a redactable one.

Chameleon 哈希算法提供了一个后门来高效计算 collision-resistant。因此将改哈希算法整合到区块链的话就可以构造出一个可编辑的区块链。

Research Summary

A framework to redact and compress the content of blocks in virtually any blockchain based technology as implementing a redactable blockchain requires only minor modifications to the current structure of the blocks.

论文提出了一种可适用于所有区块链系统的可编辑、压缩区块内容的框架，因为只需要对区块链上区块的数据结构做少量的更改即可。

Novelty

Contributions

1. Propose a new design of a redactable blockchain which is compatible with all popular blockchain proposals.
2. Improved chameleon hash function design.

3. Implementation of redactable blockchain.

4. 提出一种新型可编辑区块链的设计方案，可兼容于所有主流的区块链方案。
5. 改进了Chameleon哈希算法设计。
6. 实现了一个可编辑区块链。

Key Concepts

Hash Function

A hash function is any function that can be used to map data of arbitrary size to data of a fixed size. A cryptographic hash function allows one to easily verify that some input data maps to a given hash value, but if the input data is unknown, it is deliberately difficult to reconstruct it (or any equivalent alternatives) by knowing the stored hash value.

Collision resistant

1. a hash function H is collision resistant: for a fixed input a, it is hard to find another input b such that H(a) = H(b),and a ≠ b.
2. more strictly: a hash function H is collision resistant if it is hard to find two inputs that hash to the same output; that is, two inputs a and b such that H(a) = H(b), and a ≠ b.

Chameleon Hash Function

Informally, a chameleon hash is a cryptographic hash function that contains a trapdoor: Without the trapdoor, it should be hard to find collisions, but knowledge of the trapdoor information allows collisions to be generated efficiently.