Fit for Purpose Blockchains

by Manu Sporny, Dave Longley, Dave Lehn, and Adam Lake

A White Paper from Rebooting the Web of Trust III

Abstract

At some point in the next 5-10 years there will be tens to hundreds of thousands of blockchains. Like databases today, each blockchain will be specifically tuned to its problem domain. There will also be a need for standards related to how these systems interoperate. Successful standards (e.g. TCP, IP, JSON, HTML) tend to be layered, modular, and solve a fairly small problem domain. This paper explores the types of modular standards that may be useful in a predicted future blockchain ecosystem containing tens to hundreds of thousands of interoperable blockchains.

Introduction

We have performed a feature analysis of existing blockchain technologies with a particular focus on well defined security, privacy, and performance principles. This analysis has led us to discover a number of modular components related to blockchain technologies that may eventually be good candidates for standardization.

The Technologies

For our study, we picked the following blockchain technologies with a particular focus on their ability to be used for "identity management" related activities:

• Bitcoin
• Ethereum
• Stellar
• IPFS
• Blockstack, and
• Hashgraph

Security, Privacy, and Performance Principles

We studied each Blockchain technology with a particular focus on the following security, privacy, and performance principles:

• Confidentiality - Asserts that information is not made available or disclosed to unauthorized individuals, entities, or processes.
• Integrity - Asserts that information accuracy and completeness of data over its entire life-cycle is maintained and assured.
• Non-repudiation - Asserts that one party of a transaction cannot deny having received a transaction nor can the other party deny having sent a transaction.
• Information Availability - Asserts that all information to perform a particular action must be available when it is needed.
• Provenance - Asserts that the the chronology of ownership, custody, or location of a piece of information can be traced throughout time.
• Pseudonymity - Asserts that interactions do not expose an entity’s true name or legal identity.
• Selective Disclosure - A situation where an entity may disclose information to one or more selected entities without disclosing that information outside of the selected set.
• Consistency - Asserts that all nodes in a decentralized system see the same data at the same time.
• System Availability - Asserts that every request receives a response about whether it succeeded or failed.
• Failure Tolerance - Asserts that the a decentralized system continues to operate despite arbitrary partitioning due to network failures.
• Scalability - A characteristic of a system that states how performance characteristics change as the system grows or shrinks in size.
• Latency - A characteristic of a system that states how much time it takes to complete certain operations.
• Auditability - A characteristic of a system that ensures that the complete system state can be verified at any given time to be correct.
• Liveliness - A characteristic of a system that states that all data requested may be retrieved from the system at any point.
• Denial of Service Resistance - A measure of a system’s ability to respond to requests when under extreme load. Typically, a mechanism is utilized that is capable of determining a valid request from an invalid one or that makes the price the attacker must pay far greater than the price the receiver must pay to execute the request.
• System Complexity - The level of complexity in the system that exists to achieve a set of tasks.

Summary of Research Findings

The analysis of these results led to the following two tables that summarize the research findings:

• Security Principles Summary Chart
• Performance Principles Summary Chart

Identified Features

The analysis also produced the following list of features that are either common to a subset of blockchain systems or are unique to systems related to the solution domain. The list is not meant to be exhaustive, but rather suggestive of potential areas for future standardization:

• Mirroring - A common feature of ledgers and distributed databases whereby copies of the same data is stored on multiple nodes, providing resilience and high-availability.
• Content-based Addressing - A feature of IPFS whereby content is addressed by a cryptographic hash of the content itself, providing an implicit check on data integrity.
• Proof-of-Work - A message ordering mechanism for a decentralized system that achieves consensus and deters bad actors by requiring participants to expend considerable resources.
• Gossip Protocol - An efficient communication method used by peers in Hashgraph to transmit their view of events that have occurred in order to achieve consensus.
• Digital Signatures - A cryptographic scheme for demonstrating the authenticity and integrity of digital documents.
• Public Keys - A cryptographic key that can be obtained by anyone and used to verify digital signatures. Public keys can also function as pseudonyms.
• Permissioned Ledger - A ledger where participants must be pre-authorized and authenticate themselves in order to write to the ledger.
• Hash Chaining - A mechanism for cryptographically linking sets of information together. A blockchain utilizes hash chaining, where a current block includes the hash of the previous block, to express the order in which events occurred in the system.
• Merkle Proof Receipts - A mechanism for storing the root of a Merkle tree in a blockchain and then externally providing a receipt containing a path from the hash of some private data in the Merkle tree to the root in order to establish Proof-of-Publication..
• Cross-chain Linking - The ability to natively reference one ledger from another; bi-directional links may also be possible.
• Linked Data Identifiers - In Linked Data, identifiers are URLs that can be dereferenced, typically via the Web, to find machine-readable data, usually containing more Linked Data.
• HTTP API - An application interface used to build software on the Hypertext transfer protocol, the foundation of data communication for the World Wide Web.
• Ledger Query Format - A placeholder for a future standardized query format for ledgers.
• Linked Data - A method of publishing structured, machine-readable data so that it can be interlinked, typically using URLs that can be dereferenced via the Web, and become more useful through semantic queries.
• JSON Storage - A mechanism for storing data as JSON documents.
• IPLD - InterPlanetary Linked Data, a data model representation format that enables a content addressable system to also contain named paths.
• Zero Knowledge Proofs - Is a method by which one party (the prover) can prove to another party (the verifier) that a given statement is true, without conveying any information apart from the fact that the statement is indeed true.
• Proof-of-Signature - A cryptographic method of consensus that is capable of determining if a particular piece of data was signed by a known entity.
• Proof-of-Stake - A cryptographic method of consensus where an individual vote is adjusted by a particular factor based on how much “ownership” that individual has over a particular system.
• On-ledger Key Management - Management and identification of cryptographic keys is performed directly on a ledger.
• Web-based Key Management - Management, identification, and representation of cryptographic keys via the Web and Linked Data semantics.
• Out of Band Key Management - Cryptographic key management is unspecified within the public key infrastructure. Applications must design and implement their own key management.
• Certificate Revocation Lists - A CRL can be checked by a verifier of a credential to determine if the credential is still deemed to be valid by the issuer.
• OCSP - An alternative to Certificate Revocation Lists, the Online Certificate Status Protocol (OCSP) is an Internet protocol used for obtaining the revocation status of an X.509 digital certificate over HTTP.
• Off-chain Lightning Protocols - A method of communication that bypasses the blockchain to directly communicate a series of high frequency transactions that are then hashed and placed into a blockchain.
• Sharding - The ability to create horizontal partitions of data in a database. Each individual partition is referred to as a shard and is held on a separate database server instance to spread load.
• Longest Chain Wins - The chain of blocks that required the greatest amount of cumulative “work”, a measure defined by the system in which this feature is used, is selected as the consensus chain.

Potential Areas for Standarization

The list of features above provide hints at potential areas of standardization:

• Communication Protocols
• Ledger Create/Write/Read HTTP API
• Consensus Algorithms
• Proof of Work
• Proof of Stake
• Stellar
• Hashgraph
• Key Management
• Rotation
• On/Off Chain
• Delegation and Recovery
• Blockchain Anchoring and Linking
• Chainpoint
• Cross-chain Linking and Blockchain URLs
• Data Structures
• Merkle Tree expression format
• Hashchain expression format
• Digital Signatures
• Smart Signatures
• Base58 Encoding
• Linked Data Signature Extensions
  • secp256k1 support
  • Multi-signature support
  • Endorsement signature support
• JSON Normalization

Fit for Purpose Blockchains

The outcome of this work could result in modular standards that could be combined into fit for purpose blockchains. A proof of concept has been created called Flex Ledger and has been deployed as a public demonstration of what this sort of standardization could achieve.

Next Steps

We would like to spend some time at Rebooting Web of Trust to try and flesh out more potential areas of standardization based on the research that we and others have done since Rebooting Web of Trust II. Specifically, we'd like to understand any gaps that others see in the analysis or areas of standardization that are not in the list in the previous section.