notes: research/papers/hardman-acdcs-and-w3c-vcs-lossless-vs-lossy

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research/papers/hardman-acdcs-and-w3c-vcs-lossless-vs-lossy ACDCs and W3C VCs: Lossless vs. Lossy summary v0.1 — 2026-10-15: drafted by Claude from the web page (version 1.1); unread by Mark; marked partner on Mark's word 2026-10-21, paraphrase only partner 510 # ACDCs and W3C VCs: Lossless vs. Lossy **Abstract.** An article by Daniel Hardman comparing Authentic Chained Data Containers (ACDCs) with the W3C Verifiable Credentials (VC) data model through an analogy to lossless and lossy media formats. It names six kinds of information it says VCs discard and ACDCs keep, describes where lossy formats fit, and cites the vLEI system and the Verifiable Voice Protocol as production uses. For architects choosing a credential format. ## Summary The article opens with RAW versus JPEG and FLAC versus MP3: lossless formats serve as the source of truth, lossy ones for distribution, and the conversion runs one way. It applies this to credentials, calling the W3C VC data model lossy (and SD-JWT and ISO mDL as well, deferred to another paper) and ACDCs lossless. Six losses follow. The trust chain: a VC references only its proximate issuer, so wider context needs external trust registries, while ACDCs link credentials by self-addressing identifiers (SAIDs) back to a root such as the Global Legal Entity Identifier Foundation (GLEIF). Time: VCs are verifiable mainly in the present, while the Key Event Receipt Infrastructure (KERI) key event log (KEL) lets a verifier judge validity at a past date. Edge weights and conditional logic: the Resource Description Framework (RDF) needs reification to put properties on relationships, while ACDC edges carry weight, operator and schema natively. Use cases beyond credentials: affidavits, sensor readings and journalists' source graphs have no holder, which ACDCs handle as attestations. Key management transparency: KERI anchors issuance to key state, uses witnesses and watchers to detect compromise, and supports pre-rotation, which VCs lack normatively. Schema stability: JSON-LD `@context` links can rot or change meaning, while ACDCs reference schemas by SAID. The article then says VCs suit low-stakes, short-lived uses within a consistent decentralized identifier (DID) ecosystem. As real-world validation it cites the GLEIF verifiable Legal Entity Identifier (vLEI) credential chain and the Verifiable Voice Protocol (VVP) as an improvement on STIR/SHAKEN. It closes by recommending ACDCs as the authoritative source with VCs generated from them when needed. ## Key terms lossless, lossy, trust chain, self-addressing identifier (SAID), key event log (KEL), property graph, reification, cryptoperiod, pre-rotation, schema stability ## Claims and their evidence - W3C VCs derive validity from the proximate issuer only and carry no cryptographic link back through the trust chain. [informative] - KERI's KEL lets a verifier determine whether a credential was valid on a specific past date despite later key rotations. [normative] - JSON-LD `@context` redefinition can change the meaning of signed data without breaking the signature. [informative] - The GLEIF vLEI system is a production system operating globally using ACDCs. [unverified] - VVP chains trust to a global root across jurisdictions where SHAKEN is deployed country by country. [unverified] ## Related Authentic Chained Data Containers (ACDC) specification; Key Event Receipt Infrastructure (KERI) specification; Verifiable Voice Protocol (VVP); How SD-JWT and ACDC are similar and different; Actors, Objects, and Linked Data. ## Provenance Drafted by Claude on 2026-10-15 from the web page at dhh1128.github.io/papers/acdc-vc-diff.html, read in full. Not yet read by Mark.

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