Editing Cryptographic hash function (section)

=== File or data identifier ===

A message digest can also serve as a means of reliably identifying a file; several [[Source Code Management|source code management]] systems, including [[Git (software)|Git]], [[Mercurial (software)|Mercurial]] and [[Monotone (software)|Monotone]], use the [[sha1sum]] of various types of content (file content, directory trees, ancestry information, etc.) to uniquely identify them. Hashes are used to identify files on [[peer-to-peer]] [[filesharing]] networks. For example, in an [[ed2k link]], an [[MD4]]-variant hash is combined with the file size, providing sufficient information for locating file sources, downloading the file, and verifying its contents. [[Magnet URI scheme|Magnet links]] are another example. Such file hashes are often the top hash of a [[hash list]] or a [[Merkle tree|hash tree]], which allows for additional benefits.

One of the main applications of a [[hash function]] is to allow the fast look-up of data in a [[hash table]]. Being hash functions of a particular kind, cryptographic hash functions lend themselves well to this application too.

However, compared with standard hash functions, cryptographic hash functions tend to be much more expensive computationally. For this reason, they tend to be used in contexts where it is necessary for users to protect themselves against the possibility of forgery (the creation of data with the same digest as the expected data) by potentially malicious participants, such as open source applications with multiple sources of download, where malicious files could be substituted in with the same appearance to the user, or an authentic file is modified to contain malicious data.<ref>{{Cite web |title=File Hashing |url=https://www.cisa.gov/sites/default/files/FactSheets/NCCIC%20ICS_Factsheet_File_Hashing_S508C.pdf |url-status=live |archive-url=https://web.archive.org/web/20250202100840/https://www.cisa.gov/sites/default/files/FactSheets/NCCIC%20ICS_Factsheet_File_Hashing_S508C.pdf |archive-date=February 2, 2025 |access-date=March 10, 2025 |website=CYBERSECURITY & INFRASTRUCTURE SECURITY AGENCY |format=PDF}}</ref>

==== Content-addressable storage ====
{{excerpt|Content-addressable storage}}