This specification describes a standard signature suite created in 2018 for the Ed25519 signature scheme using Curve25519, used e.g. by Hyperledger Indy.

This is an experimental specification and is undergoing regular revisions. It is not fit for production deployment.

Introduction

This specification describes a standard signature suite created in 2018 for the Linked Data Signatures [[LD-SIGNATURES]] specification. It uses the RDF Dataset Normalization Algorithm [[RDF-DATASET-NORMALIZATION]] to transform the input document into its canonical form. It uses SHA-256 [[RFC6234]] as the message digest algorithm and Ed25519 [[ED25519]] as the signature algorithm.

Terminology

The following terms are used to describe concepts involved in the generation and verification of the Ed25519 2018 signature suite.

signature suite
A specified set of cryptographic primitives typically consisting of a canonicalization algorithm, a message digest algorithm, and a signature algorithm that are bundled together by cryptographers for developers for the purposes of safety and convenience.
canonicalization algorithm
An algorithm that takes an input document that has more than one possible representation and always transforms it into a canonical form. This process is sometimes also called normalization.
message digest algorithm
An algorithm that takes an input message and produces a cryptographic output message that is often many orders of magnitude smaller than the input message. These algorithms are often 1) very fast, 2) non-reversible, 3) cause the output to change significantly when even one bit of the input message changes, and 4) make it infeasible to find two different inputs for the same output.
signature algorithm
An algorithm that takes an input message and produces an output value where the receiver of the message can mathematically verify that the message has not been modified in transit and came from someone possessing a particular secret.

The Ed25519 Key Format

Examples

A simple example of an Ed25519 2018 Signature Verification Key: 

{
  "@context": ["https://w3id.org/security/v2"],
  "id": "did:example:123456789abcdefghi#keys-1",
  "type": "Ed25519VerificationKey2018",
  "controller": "did:example:123456789abcdefghi",
  "expires": "2017-02-08T16:02:20Z",
  "publicKeyBase58" : "H3C2AVvLMv6gmMNam3uVAjZpfkcJCwDwnZn6z3wXmqPV"
}

Note: The publicKeyBase58 property contains the raw public key bytes. The encoding is Base58 using the same alphabet as Bitcoin addresses and IPFS hashes.

The Ed25519 2018 Signature Suite

The Ed25519 2018 signature suite MUST be used in conjunction with the signing and verification algorithms in the Linked Data Signatures [[LD-SIGNATURES]] specification. The suite consists of the following algorithms:

Parameter Value Specification
canonicalizationAlgorithm https://w3id.org/security#URDNA2015 [[RDF-DATASET-NORMALIZATION]]
digestAlgorithm http://w3id.org/digests#sha256 [[RFC6234]]
signatureAlgorithm http://w3id.org/security#ed25519 [[ED25519]]

Modification to Algorithms

No modifications to the Linked Data Signature algorithms are provided other than the algorithms specified in the previous signature suite section.

Security Considerations

The following section describes security considerations that developers implementing this specification should be aware of in order to create secure software.

TODO: We need to add a complete list of security considerations.

Examples

A simple example of a Ed25519 2018 Signature: 

{
  "@context": ["http://schema.org/", "https://w3id.org/security/v2"],
  "description": "Hello world!",
  "proof": {
    "type": "Ed25519Signature2018",
    "created": "2016-10-23T05:50:16Z",
    "verificationMethod": "did:example:123456789abcdefghi#key1",
    "proofPurpose": "assertionMethod",
    "jws" : "eyJhbGciOiJFZERTQSIsImI2NCI6ZmFsc2UsImNyaXQiOlsiYjY0Il19..AUQ3AJ23WM5vMOWNtYKuqZBekRAOUibOMH9XuvOd39my1sO-X9R4QyAXLD2ospssLvIuwmQVhJa-F0xMOnkvBg"
  }
}