Magnet URI scheme Information & Magnet URI scheme Links at HealthHaven.com

The magnet: URI scheme is a draft open standard defining a URI scheme for magnet links, which are mainly used to reference resources available for download via peer-to-peer networks. Such a link typically identifies a file not by location or name, but by content; more precisely, by the content's hash value.

Since it refers to a file based on content or metadata, rather than by location, a magnet link can be considered a kind of Uniform Resource Name, rather than the more common Uniform Resource Locators. Although it could be used for other applications, it is particularly useful in a peer-to-peer context, because it allows resources to be referenced without the need for a continuously available host.

[edit] History

The standard was developed in 2002, partly as a "vendor- and project-neutral generalization" of the ed2k: and freenet: URI schemes used by eDonkey2000 and Freenet, respectively, and attempts to follow official IETF URI standards as closely as possible. Applications supporting magnet links include Vuze, BearShare, DC++, Deluge, gtk-gnutella, Kazaa, LimeWire, FrostWire, MP3 Rocket, Morpheus, Qbittorrent (as of v1.5.0), BitComet (as of v1.17beta), BitSpirit, Shareaza, MLdonkey, aMule, KCeasy, TrustyFiles, μTorrent, and Transmission (as of v1.80b1 9679).

[edit] Use of content hashes

The most common use of magnet links is to link to a particular file based on a hash of its contents, producing a unique identifier for the file, similar to an ISBN or catalog number. Unlike traditional identifiers, however, content-based signatures can be generated by anyone who already has the file, and so do not need a central authority to issue them. This makes them popular for use as "guaranteed" search terms within the file sharing community where anyone can distribute a magnet link to ensure that the resource retrieved by that link is the one intended, regardless of how it is retrieved. (While it is technically possible that two files could have the same hash value, it is statistically very unlikely; see Cryptographic hash function).

Another advantage of magnet links is their open nature and platform independence: the same magnet link can be used to download a resource from one of any number of applications on almost any operating system. Because magnets are concise and plain-text, it is possible for users to simply copy-and-paste the links into emails or instant messages, a property not found in, for example, BitTorrent files.

[edit] Technical description

Magnet links consist of a series of one or more parameters, the order of which is not significant, formatted in the same way as the query string on the end of many HTTP URLs. The most common parameter is "xt", meaning "exact topic", which is generally a URN formed from the content hash of a particular file, e.g..

magnet:?xt=urn:sha1:YNCKHTQCWBTRNJIV4WNAE52SJUQCZO5C

referring to the Base32 encoded SHA-1 hash of the file in question. Note that although this refers to a particular file, a search must still be carried out by the client application to determine where, if anywhere, it can obtain that file.

Other parameters defined by the draft standard are:

"dn" ("display name"): a filename to display to the user, for convenience
"kt" ("keyword topic"): a more general search, specifying search terms rather than a particular file
"mt" ("manifest topic"): a URI pointing to a "manifest", e.g. a list of further items
application-specific experimental parameters, which must begin "x."

The standard also suggests that multiple parameters of the same type can be used by appending ".1", ".2" etc. to the parameter name, e.g.

magnet:?xt.1=urn:sha1:YNCKHTQCWBTRNJIV4WNAE52SJUQCZO5C&xt.2=urn:sha1:TXGCZQTH26NL6OUQAJJPFALHG2LTGBC7

[edit] Description

Magnet links can contain one or more parameters, separated from each other by '&'. The order of parameters is not documented. For some values of the parameter is important for the proper parsing client MAGNET links.

    magnet:? xl = [Size in Bytes] & dn = [file name (URL encoded)] & xt = urn: tree: tiger: [ TTH hash (Base32) ]

[edit] Parameters

dn (Display Name) - Filename
xl (eXact Length) - Size in bytes
xt (eXact Topic) - URN containing file hash
as (Acceptable Source) - Web link to the file online
xs (eXact Source) - P2P link.
kt (Keyword Topic) - Key words for search
mt (Manifest Topic) - link to the metafile that contains a list of magneto (MAGMA - MAGnet MAnifest)
tr (address TRacker) - Tracker URL for BitTorrent downloads

[edit] URN, containing hash (xt)

This part of Magnet links is the most important one. It is used to find and verify files included in the Magnet link.

TTH (Tiger Tree Hash)

TigerTree hashes are used in several networks including Direct Connect and Gnutella2.

   xt=urn:tree:tiger:[ TTH Hash (Base32) ]

SHA-1 (Secure Hash Algorithm 1)

Hash sum used on Gnutella and Gnutella2.

   xt=urn:sha1:[ SHA-1 Hash (Base32) ]

BitPrint

This hash code consists of an SHA-1 Hash followed by a TTH Hash split by a point. Hash sum used on Gnutella and Gnutella2.

   xt=urn:bitprint:[ SHA-1 Hash (Base32) ].[ TTH Hash (Base32) ]

ED2K (eDonkey2000) Hash

Hash sum used on eDonkey2000.

   xt=urn:ed2k:[ ED2K Hash (Hex) ]

AICH (Advanced Intelligent Corruption Handler)

No formal URN for Magnet links. Hash sum used on eDonkey2000 to restore and control the integrity of downloaded/downloading files.

   xt=urn:aich:[ aich Hash (Base32) ]

Kazaa Hash

Hash sum used on FastTrack.

   xt=urn:kzhash:[ Kazaa Hash (Hex) ]

BTIH (BitTorrent Info Hash)

Hash sum used on BitTorrent.

   xt=urn:btih:[ BitTorrent Info Hash (Hex) ]

MD5 (Message Digest 5)

Hash sum supported by Gnutella2.

   xt=urn:md5:[ MD5 Hash (Hex) ]

CRC-32 (Cyclic Redundancy Check)

Not a formal URN for Magnet links. Not used in any known P2P network.

   xt=urn:crc32:[ CRC-32 (Base10) ]

[edit] Web links to the file

There are two types of download links that can be inserted in a Magnet link as a direct or backup source.

[edit] Normal (as)

"as" stands for "acceptable source". This type of source refers to a direct download from a web server. It is thought to be only contacted after a certain timeout in order to avoid overloading the server by giving the client some time to locate the file in P2P networks before sending a download query to the server in question.

   as=[ a web link to the file(URL encoded) ]

[edit] P2P (xs)

This link is either an HTTP (SHTTP, FTP, SFTP, etc.) download source for the file linked to by the Magnet link, the address of a P2P source for the file or the address of a hub (in the case of DC + +). For this link a client tries to connect directly and asks for the file and/or its sources. This field is commonly used P2P clients to store the source. The reference may include the file hash.

Content-Addressable Web URL

This type of link is used by Gnutella as well G2 applications and based on RFC 2168.

   xs=http://[Client Address]:[Port of client]/uri-res/N2R?[ URN containing a file hash ]

Example:

   xs=http://192.0.2.0.27:6346/uri-res/N2R?urn:sha1:FINYVGHENTHSMNDSQQYDNLPONVBZTICF

Link to a DirectConnect hub to find sources for a file

This link connects a DirectConnect client immediately to the hub in question.

   xs=dchub://[hub address]:[hub port]

Reference to a web-based source cache for a file on Gnutella2

In this case, the link included points not to a client IP or direct source, but to a source cache. Such a cache doesn't have the file itself, but it stores the IPs of other clients contacting it to download the same file. Once a client connects to the cache to get other IPs for alternate sources, its own IP is stored inside the cache and forwarded to the next one asking for alternate sources. This system operates similar to a BitTorrent tracker.

   xs=http://cache.freebase.be/[ SHA-1 hash ]

Reference to an ED2K source

   xs=ed2kftp://[client address]:[client port]/[ed2k hash]/[file size]/

[edit] Manifest (mt)

This is a link to a list of links (see list). Perhaps as a web link...

   mt=http://weblog.foo/all-my-favorites.rss

...or an URN

   mt=urn:sha1:3I42H3S6NNFQ2MSVX7XZKYAYSCX5QBYJ

[edit] Keywords (kt)

This field specifies a string of search keywords to search for in P2P networks.

   kt=martin+luther+king+mp3

[edit] Address tracker (tr)

Tracker URL. Used to obtain resources for BitTorrent downloads without a need for DHT support.

   tr=http://example.com/announce

[edit] Supplement format (x.)

For experimental and self-complementing informal options, the prefix x followed by a chosen second letter can be used

   x.[name of the new parameter]=[data of the new parameter (URL encoded)]

[edit] Group settings

Allows to include several files and their URNs, names and hashes in the Magnet link by adding a count number preceded by a dot (".") to each link parameter.

   magnet:?xt.1=[ URN of the first file]&xt.2=[ URN of the second file]

[edit] Note

Some programs create Magnet links while not respecting URL encoding for the link parameters. These programs have around 20% market share and can create errors when used on web pages.^{[citation needed]}

[edit] Example

Link to a file of zero bytes length.

   magnet:?xt=urn:ed2k:31D6CFE0D16AE931B73C59D7E0C089C0&xl=0&dn=zero_len.fil&xt=urn:bitprint:3I42H3S6NNFQ2MSVX7XZKYAYSCX5QBYJ.   LWPNACQDBZRYXW3VHJVCJ64QBZNGHOHHHZWCLNQ&xt=urn:md5:D41D8CD98F00B204E9800998ECF8427E

[edit] Features

Client	dn	xl	xt	tr	xs	as	kt	mt	Interception^[1]	Box^[2]
ApexDC++	Yes	Yes	Urn: tree: tiger: urn: bitprint:	No	Dchub://[hubaddress]:[hubport]	Dchub://[hubaddress]:[hubport]	No	?	Yes	No
Shareaza	Yes	Yes	urn: sha1: urn: tree: tiger: urn: bitprint: urn: ed2k: urn: md5: urn: btih:	Yes ^[3]	http: ftp:	http: ftp: (Same priority as xs)	Yes	No	Yes	Yes
Azureus	?	?	urn: btih:	?	?	?	?	?	?	?
AMule	Yes	Yes	urn: ed2k:	No	?	?	?	?	No	Yes
µTorrent	Yes	No	urn: btih:	Yes	No	No	No	No	Yes	Yes

[edit] DC + + clients

Can intercept Magnet links from your browser. Therefore the Magnet link text can be inserted into the address bar of your browser. For links included in web pages, just click on the link.

[edit] Shareaza

Able to intercept links from within the web browser and has a possibility to directly insert Magnet links to the client by pasting them into the search area or the "Download File or Torrent" dialog.

[edit] aMule 2.2

"sees" only if it MAGNET insert line eD2k Link at the bottom of the client. Therefore MAGNET link must "build", copy, paste into the box and click add.

ED2K hash, size, file name should be first and in that order. The client divides the link. Data on the size of the file and its hash may be in different parts. Because of this link may not be suitable for downloading.

[edit] See also

Metalink

[edit] References

^ Ability to intercept Magnet links directly from within the web browser.^{[clarification needed]}
^ Possibility to inject the link directly into the application in question.
^ Since v2.5.1.0

[edit] External links

MAGNET-URI Project Web-site
Bitzi, a Magnet search engine / directory.
Freebase a website that uses magnet links to index freeware.

[0] Ability to intercept Magnet links directly from within the web browser.^{[clarification needed]}

[1] Possibility to inject the link directly into the application in question.

[2] Since v2.5.1.0

[1]

[2]

[3]

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