CIDv0

CIDv0 is the original version of the Content Identifier (CID) used by IPFS and related systems built on IPLD. A CIDv0 is a version 0 CID that combines a multihash of the content with a specific data format codec, and its textual representation is encoded in base58btc. The most common form identifies content that has been hashed with SHA-256 and encoded using the DAG-PB (Directed Acyclic Graph Protocol Buffers) codec. This combination yields strings typically starting with Qm and about 46 characters long.

Technical details include that the multihash portion uses the SHA-256 hash function and a 32-byte digest, while the codec portion indicates DAG-PB. As a result, CIDv0 carries no explicit version byte in its textual form and is tied to a fixed set of parameters: SHA-256 for hashing and DAG-PB for the data structure. The base58btc encoding makes CIDv0 strings compact and human-readable in many IPFS workflows.

History and usage describe CIDv0 as the default and widely deployed form in the early IPFS ecosystem. It remains common for addressing blocks and DAG-PB nodes, and many existing blocks in the IPFS network are CIDv0. However, CIDv0 is not designed to support new codecs or hash functions beyond SHA-256 with DAG-PB. For greater flexibility, CIDv1 was introduced, allowing multiple encodings and codecs and enabling future extensions while maintaining compatibility with CID concepts.

See also: CID, CIDv1, multihash, multicodec, base58btc, IPFS.