Editing Cryptographic hash function (section)

=== Verifying the integrity of messages and files ===
{{ main | File verification }}

An important application of secure hashes is the verification of [[message integrity]]. Comparing message digests (hash digests over the message) calculated before, and after, transmission can determine whether any changes have been made to the message or [[computer file|file]].

[[MD5]], [[SHA-1]], or [[SHA-2]] hash digests are sometimes published on websites or forums to allow verification of integrity for downloaded files,<ref name="e87Bo">{{cite magazine | url=http://www.techrepublic.com/blog/security/use-md5-hashes-to-verify-software-downloads/374 | title=Use MD5 hashes to verify software downloads | magazine=TechRepublic | date=December 5, 2007 | access-date=March 2, 2013 | last=Perrin | first=Chad | archive-date=October 18, 2012 | archive-url=https://web.archive.org/web/20121018075308/http://www.techrepublic.com/blog/security/use-md5-hashes-to-verify-software-downloads/374 | url-status=live }}</ref> including files retrieved using [[file sharing]] such as [[Mirror website|mirroring]]. This practice establishes a [[chain of trust]] as long as the hashes are posted on a trusted site – usually the originating site – authenticated by [[HTTPS]]. Using a cryptographic hash and a chain of trust detects malicious changes to the file. Non-cryptographic [[error-detecting code]]s such as [[cyclic redundancy check]]s only prevent against ''non-malicious'' alterations of the file, since an intentional [[Spoofing attack|spoof]] can readily be crafted to have the [[Collision attack|colliding code]] value.