What is CID ?

November 6, 2025 ยท View on GitHub

CID (Content IDentifier)

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What is CID ?

CID <https://github.com/ipld/cid>_ is a format for referencing content in distributed information systems, like IPFS <https://ipfs.io>. It leverages content addressing <https://en.wikipedia.org/wiki/Content-addressable_storage>, cryptographic hashing <https://simple.wikipedia.org/wiki/Cryptographic_hash_function>, and self-describing formats <https://github.com/multiformats/multiformats>.

It is the core identifier used by IPFS <https://ipfs.io>_ and IPLD <https://ipld.io>_.

CID is a self-describing content-addressed identifier.

It uses cryptographic hashes to achieve content addressing.

It uses several multiformats <https://github.com/multiformats/multiformats>_ to achieve flexible self-description, namely multihash <https://github.com/multiformats/multihash>_ for hashes, multicodec <https://github.com/multiformats/multicodec>_ for data content types, and multibase <https://github.com/multiformats/multibase>_ to encode the CID itself into strings.

Sample Usage

.. code-block:: python

>>> from cid import make_cid
>>> make_cid('QmaozNR7DZHQK1ZcU9p7QdrshMvXqWK6gpu5rmrkPdT3L4')
CIDv0(version=0, codec=dag-pb, multihash=b"\x12 \xb9M'\xb9\x93M>\x08\xa5.R\xd7\xda}\xab\xfa\xc4\x84..")

>>> cid = make_cid('QmaozNR7DZHQK1ZcU9p7QdrshMvXqWK6gpu5rmrkPdT3L4')
>>> print(cid.version, cid.codec, cid.multihash)

>>> print(cid.encode())
QmaozNR7DZHQK1ZcU9p7QdrshMvXqWK6gpu5rmrkPdT3L4

>>> str(cid)
'QmaozNR7DZHQK1ZcU9p7QdrshMvXqWK6gpu5rmrkPdT3L4'

Other info