Ed25519Signature2020

Ed25519Signature2020 is a standardized cryptographic suite defined by the W3C for creating and verifying digital signatures on Linked Data documents, such as Verifiable Credentials (VCs) and Verifiable Presentations. It specifies the use of the Ed25519 elliptic curve digital signature algorithm, which is known for its high performance, strong security, and small key sizes. This suite provides a concrete set of rules for canonicalizing data, creating a cryptographic digest, and generating a signature that can be independently verified, ensuring data integrity and authentication in decentralized identity systems.

The suite operates by first transforming the input JSON-LD data into a deterministic form through a process called URDNA2015 canonicalization (also known as RDF Dataset Canonicalization). This step is critical for Linked Data, as the same semantic information can be expressed in multiple syntactically different JSON documents. After canonicalization, the data is hashed using the SHA-256 algorithm to produce a digest. The Ed25519 private key is then used to sign this digest, resulting in a Ed25519Signature2020 data integrity proof that is attached to the original document.

A key component of this proof is the verification method, which is typically expressed as a DID URL (e.g., did:example:123#key-1) pointing to the public key within a Decentralized Identifier (DID) document. This creates a strong, cryptographically verifiable link between the issuer of a credential, their public key, and the signed data. The suite's design ensures selective disclosure is possible when combined with other technologies, though the base Ed25519Signature2020 itself produces a signature over the entire canonicalized dataset.

Ed25519Signature2020 is a cornerstone of the W3C Verifiable Credentials Data Model, providing a practical and widely implemented signature option. Its advantages include speed and security, making it suitable for environments requiring high-throughput verification, such as mobile or IoT contexts. When comparing suites, it is often contrasted with JSON Web Signatures (JWS) and other suites like EcdsaSecp256k1Signature2019, with the primary differentiators being its reliance on RDF canonicalization and its native integration with the Linked Data proof format.

Developers implement this suite by following the specification to create a DataIntegrityProof with type set to Ed25519Signature2020. The proof object includes the verification method, proof purpose (e.g., assertionMethod), the signature value itself, and a created timestamp. Libraries such as jsonld-signatures and vc-js provide built-in support for creating and verifying these proofs, handling the complex steps of canonicalization and signing transparently.

Ed25519Signature2020 is a Linked Data Proof cryptosuite defined in the W3C Verifiable Credentials Data Integrity specification that uses the Ed25519 elliptic curve digital signature algorithm to create and verify proofs on JSON-LD documents. It provides a standardized method for generating a cryptographic signature over a canonicalized and hashed representation of the data, ensuring the integrity and authenticity of the signed information. This suite is distinguished by its use of the RDF Dataset Canonicalization (RDFC-1.0) algorithm and the SHA-256 hash function to create a deterministic data payload before signing, which is critical for interoperability across different systems.

The signing process follows a precise sequence: first, the input JSON-LD document is transformed into an RDF dataset using a JSON-LD processor. This dataset is then canonicalized using RDFC-1.0, producing a unique, deterministic N-Quads representation. The canonicalized data is hashed with SHA-256 to create the final payload for the signature. The signer's private key, corresponding to an Ed25519 public key listed in a verification method within the document, is used to generate the Ed25519Signature2020 proof object. This proof contains the signature value itself and metadata such as the proofPurpose, verificationMethod, and created timestamp.

Verification is the inverse process. The verifier retrieves the signer's public key from the verificationMethod, re-computes the canonicalization and hash of the document (excluding the proof), and uses the Ed25519 algorithm to check the signature against the computed hash. A successful verification proves that the data has not been altered since it was signed by the holder of the corresponding private key. This process is selective disclosure-ready; the suite can be used with mechanisms like BBS+ signatures for derived proofs, though Ed25519Signature2020 itself creates signatures over the entire disclosed data set.

A key advantage of Ed25519Signature2020 is its performance and wide support. The Ed25519 algorithm is known for its fast verification speeds, small key sizes, and built-in resilience to common cryptographic pitfalls. As a Data Integrity suite, it is a foundational building block for Verifiable Credentials (VCs) and Decentralized Identifiers (DIDs), enabling use cases like digital driver's licenses, educational credentials, and professional certifications. Its standardization within the W3C ecosystem ensures it can be implemented consistently across various verifiable data registry platforms and agent frameworks.

When implementing this suite, developers must ensure correct canonicalization, as even semantically identical JSON-LD documents with different key orders or formatting will produce different canonical hashes, causing verification to fail. The suite is typically identified by the type property set to "Ed25519Signature2020" within a proof object. It represents a move away from older, less secure proof types like Ed25519Signature2018, incorporating modern cryptographic standards and the rigorous data integrity model defined by the W3C.

The Ed25519Signature2020 is a Linked Data Proof suite defined by the W3C that uses the Ed25519 digital signature algorithm to create and verify cryptographically secure proofs on JSON-LD documents. It is formally specified in the W3C Verifiable Credentials Data Integrity specification, providing a standardized method for ensuring data integrity and authenticity in decentralized identity ecosystems like Verifiable Credentials (VCs) and Decentralized Identifiers (DIDs). The suite's name follows a common pattern in the W3C ecosystem: the cryptographic algorithm (Ed25519) followed by the proof purpose (Signature) and the year of its primary specification (2020).

The etymology of the term is directly derived from its core components. Ed25519 refers to the Edwards-curve Digital Signature Algorithm using the twisted Edwards curve over the finite field defined by the prime 2^255 - 19, a highly efficient and secure algorithm developed by Daniel J. Bernstein et al. The Signature component indicates its primary function as a digital signature mechanism for non-repudiation. The 2020 suffix denotes the year the cryptographic suite was formally introduced and standardized within the W3C's Verifiable Credentials working group, distinguishing it from potential future iterations or similar suites.

Technically, the suite specifies the exact cryptographic primitives and data serialization methods required for interoperability. This includes the use of the Ed25519 algorithm for signing, the SHA-256 hash function for creating the data to be signed (the proof hash), and a strict JSON-LD canonicalization algorithm (like URDNA2015) to ensure the data is serialized identically for both signer and verifier. The specification mandates the format of the resulting proof object, which includes essential fields like type, verificationMethod, created, and the proofValue (the Base58-encoded signature).

Its role within the specification is to provide a concrete, testable implementation profile for Data Integrity proofs. Unlike a general description of Ed25519, the Ed25519Signature2020 suite defines precisely how to use the algorithm within the context of Linked Data and the Verifiable Credentials data model. This eliminates ambiguity for developers, ensuring that a proof created by one software library can be validated by another, fostering ecosystem interoperability. It is a key building block for trust in decentralized systems where cryptographic verification replaces centralized authorities.

In practice, the specification addresses critical security considerations such as key rotation, proof purpose validation (e.g., assertionMethod or authentication), and protection against replay attacks through the use of the created timestamp and optional challenge or domain parameters. By bundling these conventions with the core signing algorithm, Ed25519Signature2020 elevates a raw cryptographic primitive into a full-fledged, context-aware verification protocol suitable for the complex graph-based data structures of the semantic web.