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This comprehensive explanation has been generated from 35 GitHub source documents. All source documents are searchable here.
Last updated: October 7, 2025
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A standardized two-part identifier (type/subtype) that indicates the nature and format of file or data content transmitted over the internet, registered and maintained by IANA (Internet Assigned Numbers Authority).
A media type (historically known as MIME type) is a standardized mechanism for identifying the nature and format of files and data streams transmitted over the internet. Media types use a structured type/subtype format (e.g., image/jpeg, application/json) to enable systems to correctly interpret and handle different content types.
The Internet Assigned Numbers Authority (IANA) serves as the official standardization body responsible for registering, publishing, and maintaining the authoritative registry of media types. While IANA registration is ideal, experimental or proposed media types are also considered valid during development and standardization processes.
Within the KERI ecosystem, media types serve as the primary differentiation mechanism for various credential formats and verifiable data structures:
The foundational media type for credentials is credential+ld+json, combining:
credential - identifies the resource as a credentialld - indicates Linked Data formatjson - specifies JSON serializationACDC (Authentic Chained Data Container) credentials use with a critical design decision: . The rationale is that can dynamically alter semantic meaning, introducing potential ambiguity and security risks. By omitting , ACDCs maintain semantic consistency and cryptographic stability.
When implementing KERI/ACDC systems:
application/json, application/cbor)The exclusion of @context in ACDC media types reflects a fundamental design principle: semantic meaning must be stable and deterministic. Systems processing credential+acdc+json can rely on fixed semantic interpretation without dynamic context resolution, which is critical for cryptographic verification and legal enforceability of credentials.
KERI/ACDC systems should support multiple serialization formats with corresponding media types:
credential+acdc+json for human-readable credentialscredential+acdc+cbor for compact binary encodingcredential+acdc+msgpack for MessagePack serializationapplication/cesr for streaming event datacredential+acdc+json@context field@context@contextACDCs maintain compatibility with W3C Verifiable Credentials through transformation mechanisms:
credential+ld+json)Media types are essential for identifying CESR (Composable Event Streaming Representation) encoded content streams. The IANA media type application/cesr (in standardization) will enable proper content negotiation and handling of CESR-encoded KERI event streams, which combine KEL (Key Event Log) and TEL (Transaction Event Log) data.