What is a CID? An IPFS content identifier

An IPFS CID, or content identifier, identifies data using a cryptographic digest and the format information needed to interpret it. Unlike a server address, it is tied to content.

A CID is not always the raw file's SHA-256 digest. Chunking, encoding and import settings can affect the result. Reproducing an identifier requires compatible choices as well as the same file.

Example: Changing one number in a document

A contract changes a payment from $100 to $120. Even if the file keeps its name and is imported with the same settings, the changed contents produce a different CID. The old identifier still refers to the old contents; it does not silently update to the new wording.

Knowing a valid identifier proves neither that the information is trustworthy nor that a copy is continuously available. A document containing false claims can have a CID too. Retrieval still requires a reachable copy of the data.

Sources

• IPFS content addressing