Glossary

Agent

A software component that manages signing keys and delegations needed to invoke w3up APIs.

Agents are used to invoke capabilities provided by the w3up service layer, using the ucanto RPC framework.

Agents are created locally on an end-user's device, and users are encouraged to create new agents for each device (or browser) that they want to use, rather than sharing agent keys between devices.

Audience

The intended recipient of a UCAN token, identified by DID

Each UCAN token is "addressed to" a specific principal, known as the audience.

When invoking a capability, the service provider is the audience of the invocation.

When delegating permissions, the audience is the party receiving the delegation.

Bitswap

A peer-to-peer protocol used by IPFS and Filecoin to distribute blocks of data throughout the network.

While the w3up APIs do not use Bitswap directly, once data is stored with web3.storage it is made available via Bitswap to the larger IPFS network.

Block

A chunk of binary data that can be identified by CID.

Data stored with web3.storage is encoded into blocks, with large files consisting of several blocks linked together.

Blocks can be uniquely identified by CID (Content Identifier), and are often bundled into Content Archives (CARs) for transport and storage.

CAR

A collection of blocks, packaged for storage and transport.

CARs are like a tar file for content-addressed data.

Used extensively by w3up protocols, although most users shoudn't be exposed to them directly for the most common operations.

CID

A Content Identifier that uniquely and verifiably identifies a block of data.

A CID consists of a cryptographic hash of the data it identifies, as well as a few bytes of metadata indicating what format the content is expected to be in.

See the IPFS docs for more details.

DAG

A Directed Acyclic Graph data structure.

A Directed Acyclic Graph (DAG) is a data structure that represents a collection of linked objects ("nodes"), where the links between nodes ("edges") have certain properties. For example, you can't have "cycles" or loops in the graph, where following a set of edges brings you back to the node you started from.

IPFS encodes files and directories into DAGs comprised of blocks of data, where each block can optionally link to other blocks using its CID.

Most DAGs will have a single "root" node which represents the "top" of the graph. By starting at the root node and traversing the links, you can find all the blocks that make up the DAG.

DHT

A Distributed Hash Table allows many peers in a peer-to-peer network to locate each other and coordinate to provide services.

IPFS uses a DHT to advertise content to the network, making it discoverable to all peers who query the DHT. The DHT does not contain the full content - instead a small "provider record" contains addresses of peers who will serve the content on request (e.g. via Bitswap).

Content stored with web3.storage is discoverable via the public IPFS DHT.

DID

A decentralized identifier that contains or links to a cryptographic public key.

DIDs are decentralized identifiers that don't rely on any single authority to issue and validate.

See our DID intro article for more details.

Elastic IPFS

A "cloud-native" IPFS implementation developed by Protocol Labs.

Elastic IPFS is an implementation of IPFS designed to leverage cloud storage for scalability and efficient retrieval.

Content is stored on commodity cloud storage (e.g. Amazon S3, Cloudflare R2) in CAR format, along with indexes that allow efficient location and retrieval of data within the CARs.

Elastic IPFS interoperates with the public IPFS network by making content available via Bitswap.

Gateway

An IPFS gateway allows retrieving IPFS content via HTTP, allowing any web browser to access data stored with IPFS.

Gateways act as a "bridge" between IPFS's peer-to-peer protocols and the HTTP protocol used by web browsers.

You can fetch IPFS content from a gateway by creating a gateway URL from the CID of your content,

To use the web3.storage gateway at w3s.link, make a URL like this, replacing ${cid} with the CID you want to link to:

https://${cid}.ipfs.w3s.link

IPFS

The InterPlanetary File System, a distributed system for sharing and linking to content-addressed data.

IPFS is a system for organizing, locating, and transmitting data using cryptographic hashes to identify each piece of content. There are many IPFS implementations, which work together to form a public network (as well as specialized private networks). web3.storage makes all uploaded content available to the IPFS network via Bitswap, as well as via HTTP through gateways.

IPLD

InterPlanetary Linked Data is a collection of data formats that can be linked together by CID.

IPLD is a specification for data types that can be linked together by CID to form a DAG.

UnixFS is an IPLD data format, but IPLD also supports JSON, CBOR, and other encodings for structured data that do not need the "file-like" metadata included in UnixFS.

See the IPLD website for more information.

Issuer

The creator and signer of a UCAN token, identified by DID.

Each UCAN token must be signed by the private key belonging to the issuer.

When invoking a capability, the issuer is the agent executing the invocation.

When delegating permissions, the issuer is the agent who currently possesses the given permissions and is delegating them to another agent (the audience).

Space

A unique identifier that acts as a "namespace" for uploaded content.

The w3up APIs use "spaces" to group uploads together, similar to how cloud storage buckets group stored objects.

Spaces act as the "destination" for uploaded data, and permissions to write to and/or manage a space can be delegated to multiple agents.

UCAN

User Controlled Authorization Networks are an authentication and authorization protocol designed for decentralized systems.

The w3up APIs use UCAN extensively to provide services and authorize invocations.

See our intro to UCAN article for an overview.

ucanto

A remote procedure call (RPC) framework based on UCANs.

The UCAN-based w3up APIs are implemented using the ucanto framework.

ucanto provides the "plumbing" for type-safe UCAN-based APIs, allowing services to define capability handlers which can be invoked by authorized clients.

UnixFS

A data format used by IPFS to represent files and directories.

UnixFS is a data format used by IPFS to encode files and directories into a DAG structure. When preparing data for IPFS, the UnixFS encoder will chunk files into blocks that are linked by CID.

UnixFS is used by IPFS on all operating systems, including Windows. The name indicates that the format supports some common metadata used on Unix platforms, for example, symbolic links and modification time.

w3up

The name of web3.storage's UCAN-based storage platform.

When web3.storage first launched, it offered a traditional "RESTful" / "JSON over HTTP" API, aimed at getting traditional web developers tapped into the potential of decentralized, content addressed storage.

After learning a lot from our first iteration, we created a new API backed by Elastic IPFS that leverages UCANs to provide secure and flexible authorization that can integrate with traditional web apps as well as fully decentralized smart contract applications.

The new APIs are provided by a collection of ucanto services and are collectively known as "w3up" to distinguish them from our "v1" RESTful API.

You can learn more about the motivations for w3up in our beta announcement blog post.