Editing Hyphanet (section)

===Keys===
Keys are [[hash function|hashes]]: there is no notion of [[semantic closeness]] when speaking of key closeness. Therefore, there will be no correlation between key closeness and similar popularity of data as there might be if keys did exhibit some semantic meaning, thus avoiding bottlenecks caused by popular subjects.

There are two main varieties of keys in use on Freenet, the Content Hash Key (CHK) and the Signed Subspace Key (SSK). A subtype of SSKs is the Updatable Subspace Key (USK) which adds versioning to allow secure updating of content.

A CHK is a [[SHA-256]] hash of a document (after encryption, which itself depends on the hash of the plaintext) and thus a node can check that the document returned is correct by hashing it and checking the digest against the key. This key contains the meat of the data on Freenet. It carries all the binary data building blocks for the content to be delivered to the client for reassembly and decryption. The CHK is unique by nature and provides tamperproof content. A hostile node altering the data under a CHK will immediately be detected by the next node or the client. CHKs also reduce the redundancy of data since the same data will have the same CHK and when multiple sites reference the same large files, they can reference to the same CHK.<ref>{{cite web|title=freesitemgr, code for inserting files as CHK, fixed revision|website=[[GitHub]]|url=https://github.com/freenet/lib-pyFreenet/blob/b78aea05222c4afe5145d8b529d2a54d4b93887a/fcp/sitemgr.py#L976|access-date=29 November 2017|archive-date=5 February 2022|archive-url=https://web.archive.org/web/20220205041918/https://github.com/freenet/pyFreenet/blob/b78aea05222c4afe5145d8b529d2a54d4b93887a/fcp/sitemgr.py#L976|url-status=live}}</ref>

SSKs are based on public-key cryptography. Currently Freenet uses the [[Digital Signature Algorithm|DSA]] algorithm. Documents inserted under SSKs are signed by the inserter, and this signature can be verified by every node to ensure that the data is not tampered with. SSKs can be used to establish a verifiable [[pseudonymity|pseudonymous]] identity on Freenet, and allow for multiple documents to be inserted securely by a single person. Files inserted with an SSK are effectively [[Immutable object|immutable]], since inserting a second file with the same name can cause collisions. USKs resolve this by adding a version number to the keys which is also used for providing update notification for keys registered as bookmarks in the web interface.<ref>{{cite web|last1=Babenhauserheide|first1=Arne|title=USK and Date-Hints: Finding the newest version of a site in Freenet's immutable datastore|url=http://draketo.de/light/english/freenet/usk-and-date-hints|website=draketo.de|access-date=29 November 2017|archive-date=8 February 2015|archive-url=https://web.archive.org/web/20150208101405/http://draketo.de/light/english/freenet/usk-and-date-hints|url-status=live}}</ref> Another subtype of the SSK is the Keyword Signed Key, or KSK, in which the key pair is generated in a standard way from a simple human-readable string. Inserting a document using a KSK allows the document to be retrieved and decrypted if and only if the requester knows the human-readable string; this allows for more convenient (but less secure) [[Uniform Resource Identifier|URIs]] for users to refer to.<ref>{{cite web|last1=Babenhauserheide|first1=Arne|title=Effortless password protected sharing of files via Freenet|url=http://draketo.de/light/english/freenet/effortless-password-protected-sharing-files|website=draketo.de|access-date=29 November 2017|archive-date=10 September 2015|archive-url=https://web.archive.org/web/20150910030851/http://draketo.de/light/english/freenet/effortless-password-protected-sharing-files|url-status=live}}</ref>