5 SSI architecture: the big picture

 

by Daniel Hardman

The purpose of this chapter is to take the basic building blocks, usage scenarios, and benefits we introduced in Part 1 and place them into an overarching picture of SSI architecture. As we will keep repeating, SSI is young, and as this chapter will explore, many facets are still in formation. Still, the basic layering has emerged, along with several of the key underpinning standards, so the main questions are how they will be implemented and how interoperable they might be depending on the design choices. In this chapter, Daniel Hardman, VP Architecture of Evernym and a major contributor to most of the core standards and protocols discussed here, will walk you through four levels of SSI architecture, the key components and technologies at each level, and the critical design decisions facing architects and implementers throughout the stack. This chapter sets the stage for the rest of the chapters in Part 2 that dive deeper into specific SSI technologies.

In chapter 2 we discussed the basic building blocks of self-sovereign identity (SSI). Those building blocks represent important commonality—all approaches to the problem agree on them. However, like automobile design in the early 1900s, the young market is producing much innovation and divergence in the details. Some are inventing with two wheels, some with four or three. Some favor steam, while others favor internal combustion engines powered by gasoline or diesel.

5.1       The SSI stack

 
 

5.2       Layer 1: Identifiers and public keys

 
 
 

5.2.1   Blockchains as DID registries

 
 

5.2.2   Adapting general purpose public blockchains to SSI

 
 

5.2.3   Special-purpose blockchains designed for SSI

 
 
 

5.2.4   Conventional databases as DID registries

 

5.2.5   Peer-to-peer protocols as DID registries

 
 
 
 

5.3       Layer 2: Secure communication and interfaces

 
 
 

5.3.1   Web-based protocol design using TLS

 
 
 
 

5.3.2   Message-based protocol design using DIDComm

 
 
 

5.3.3   Interface design options

 

5.3.4   API-oriented interface design using wallet dapps

 
 
 

5.3.5   Data-oriented interface design using hubs

 
 

5.3.6   Message-oriented interface design using agents

 
 
 

5.4       Layer 3: Credentials

 
 

5.4.1   JSON Web Token format

 
 

5.4.2   Blockcerts format

 
 
 

5.4.3   W3C verifiable credential formats

 
 

5.4.4   Credential exchange protocols

 
 

5.5       Layer 4: Governance frameworks

 
 
 
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