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C4 ID - Universally Unique and Consistent Identification

Go Report Card Build Status GoDoc MIT License

import ""

This is a Go package that implements the C4 ID system SMPTE standard ST 2114:2017. C4 IDs are universally unique and consistent identifiers that standardize the derivation and formatting of data identification so that all users independently agree on the identification of any block or set of blocks of data.

C4 IDs are 90 character long strings suitable for use in filenames, URLs, database fields, or anywhere else that a string identifier might normally be used. In ram C4 IDs are represented in a 64 byte "digest" format.


  • A single C4 id can represent multiple files.
  • C4 ids are unique, random, and unforgeable.
  • C4 ids are identical for the same file in different locations or points in time.
  • A network connection is not required to generate C4 ids.
  • A C4 id can be used in filenames, URLs, json and xml.
  • C4 ids can be selected easily with double click (a problem for many unique identifiers).
  • Easily discover C4 ids in arbitrary text with a simple regex c4[1-9A-HJ-NP-Za-km-z]{88}
  • Naming files by their C4 id automatically deduplicates them.

Comparison of Encodings

C4 is the shortest self identifying SHA-512 encoding and is the only standardized encoding. To illustrate, the following is the SHA-512 of "foo" in hex, base64 and c4 encodings:

# encoding     length   id
  hex          135:     sha512-f7fbba6e0636f890e56fbbf3283e524c6fa3204ae298382d624741d0dc6638326e282c41be5e4254d8820772c5518a2c5a8c0c7f7eda19594a7eb539453e1ed7
  base64        95:     sha512-9/u6bgY2+JDlb7vzKD5STG+jIErimDgtYkdB0NxmODJuKCxBvl5CVNiCB3LFUYosWowMf37aGVlKfrU5RT4e1w==
  c4            90:     c43inc2qGhSWQUMRvDMW6GAjJnRFY5sxq399wcUcWLTuPai84A2QWTfYu1gAW8f5FmZFGeYpLsSPyrSUh9Ao3J68Cc

Example Usage

package main

import (


func main() {

  // Generate a C4 ID for any contiguous block of data...
  id := c4.Identify(strings.NewReader("alfa"))
  // output: c43zYcLni5LF9rR4Lg4B8h3Jp8SBwjcnyyeh4bc6gTPHndKuKdjUWx1kJPYhZxYt3zV6tQXpDs2shPsPYjgG81wZM1

  // Generate a C4 ID for any number of non-contiguous blocks...
  var ids c4.IDs
  var inputs = []string{"alfa", "bravo", "charlie", "delta", "echo", "foxtrot", "golf", "hotel", "india"}
  for _, input := range inputs {
    ids = append(ids, c4.Identify(strings.NewReader(input)))
  // output: c435RzTWWsjWD1Fi7dxS3idJ7vFgPVR96oE95RfDDT5ue7hRSPENePDjPDJdnV46g7emDzWK8LzJUjGESMG5qzuXqq


Current release: v0.8.0



C4 ID Whitepaper


Contributions are welcome. The following are some general guidelines for project organization. If you have questions please open an issue.

The master branch holds the current release, and older releases can be found by their version number. The dev branch represents the development branch from which bug and feature branches should be taken. Pull requests that are accepted will be merged against the dev branch and then pushed to versioned releases as appropriate.

Feature and bug branches should follow the github integrated naming convention. Features should be given the new tag, and bugs the bug tag. Here is an example of checking out a feature branch:

> git checkout dev
Switched to branch 'dev'
Your branch is up-to-date with 'origin/dev'.
> git checkout -b new/#99_some_github_issue

If a branch for an issue is already listed in this repository, then check it out and work from it.


This software is released under the MIT license. See LICENSE for more information.