Magnet URI scheme

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Rounded magnet icon used on The Pirate Bay TPB Magnet Icon.gif
Rounded magnet icon used on The Pirate Bay

Magnet is a URI scheme that defines the format of magnet links, a de facto standard for identifying files (URN) by their content, via cryptographic hash value rather than by their location.

Contents

Although magnet links can be used in a number of contexts, they are particularly useful in peer-to-peer file sharing networks because they allow resources to be referred to without the need for a continuously available host, and can be generated by anyone who already has the file, without the need for 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.

History

The standard for Magnet URIs was developed by Bitzi 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. BitTorrent introduced the btmh: protocol in 2020 as part of its BitTorrent v2 changes. [1]

Format

Magnet URIs consist of a series of one or more parameters, the order of which is not significant, formatted in the same way as query strings that ordinarily terminate HTTP URLs.

The following parameters are supported: [2] [3]

ParameterNameDescription
xtExact Topic URN containing file hash. This is the most crucial part of the magnet link, and is used to find and verify the specified file. The URN is specific to the protocol, so a file hash URN under btih (BitTorrent) would be completely different from the file hash URN for ed2k
xt=urn:btih:c12fe1c06bba254a9dc9f519b335aa7c1367a88a
dnDisplay NameA filename to display to the user, for convenience.
xleXact LengthThe file size, in bytes
trAddress TRackerTracker URL; used to obtain resources for BitTorrent downloads without a need for DHT support. [3] The value must be URL encoded.
tr=http%3A%2F%2Fexample.org%2Fannounce
wsWeb SeedThe payload data served over HTTP(S)
as[ citation needed ]Acceptable SourceRefers to a direct download from a web server. Regarded as only a fall-back source in case a client is unable to locate and/or download the linked-to file in its supported P2P network(s)
as=[web link to file(URL encoded)]
xs[ citation needed ]eXact SourceEither an HTTP (or HTTPS, FTP, FTPS, etc.) download source for the file pointed 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++), by which a client tries to connect directly, asking for the file and/or its sources. This field is commonly used by P2P clients to store the source, and may include the file hash.
xs=http://[Client Address]:[Port of client]/uri-res/N2R?[ URN containing a file hash ]
xs=http://192.0.2.27:6346/uri-res/N2R?urn:sha1:FINYVGHENTHSMNDSQQYDNLPONVBZTICF
kt[ citation needed ]Keyword TopicSpecifies a string of search keywords to search for in P2P networks, rather than a particular file
kt=martin+luther+king+mp3
mt[ citation needed ]Manifest TopicLink to the metafile that contains a list of magneto (MAGMA  MAGnet MAnifest); i.e. a link to a list of links
mt=http://example.org/all-my-favorites.rss
mt=urn:sha1:3I42H3S6NNFQ2MSVX7XZKYAYSCX5QBYJ
so [4] Select OnlyLists specific files torrent clients should download, [5] indicated as individual or ranges (inclusive) of file indexes.
so=0,2,4,6-8
x.pePEerSpecifies fixed peer addresses to connect to. Used to bootstrap discovery of peers in the absence of (e.g.) trackers or DHT. [3]
x.pe=hostname:port
x.pe=ipv4-literal:port
x.pe=[ipv6-literal]:port

The standard also allows for application-specific experimental parameters, which must begin with "x".[ citation needed ]

Exact Topic (xt)

The xt parameter specifies the URN for a given p2p protocol. Its purpose is to provide a search parameter for finding the metadata to the torrent. This effectively acts as a replacement to a .torrent file, which itself contains the torrent metadata, by instead searching the p2p network (using the URN) for that metadata. Each protocol handles a URN uniquely; for example, xt=urn:btih:FFC7E738EAA4CD4ECF51EC6FD669C6CDE2C281A8 uses the btih (BitTorrent v1 protocol), so a BitTorrent client can take the hash and lookup the torrent's metadata in the BitTorrent DHT. [6] In the case of DHT the client searches through a set of pre-known nodes and requests the metadata for an infohash; those nodes will make the same request to other known nodes until eventually a swarm is found and returned.

xt also allows for a group setting. Multiple files can be included by adding a count number preceded by a dot (".") to each link parameter.[ citation needed ]

magnet:?xt.1=[ URN of the first file]&xt.2=[ URN of the second file]
Tiger Tree Hash (TTH)
These hashes are used on Direct Connect and G2 (Gnutella2), among others.
xt=urn:tree:tiger:[ TTH Hash (Base32) ]
Secure Hash Algorithm 1 (SHA-1)
These hash sums are used on gnutella and G2 (Gnutella2).
xt=urn:sha1:[ SHA-1 Hash (Base32) ]
BitPrint
Such hash sums consist of an SHA-1 Hash, followed by a TTH Hash, delimited by a point; they are used on gnutella and G2 (Gnutella2).
xt=urn:bitprint:[ SHA-1 Hash (Base32) ].[ TTH Hash (Base32) ]
ED2K (eDonkey2000) hash
These hash sums are used on eDonkey2000.
xt=urn:ed2k:[ ED2K Hash (Hex) ]
Advanced Intelligent Corruption Handler (AICH)
Not formal URNs for Magnet links, such hash sums are used by eDonkey2000 to restore and control the integrity of downloading and already downloaded files.
xt=urn:aich:[ aich Hash (Base32) ]
Kazaa hash
Used on FastTrack, these hash sums are vulnerable to hash collision attacks.
xt=urn:kzhash:[ Kazaa Hash (Hex) ]
BitTorrent info hash (BTIH)
These are hex-encoded SHA-1 hash sums of the "info" sections of BitTorrent metafiles as used by BitTorrent to identify downloadable files or sets of files. For backwards compatibility with existing links, clients should also support the Base32 encoded version of the hash. [3]
xt=urn:btih:[ BitTorrent Info Hash (Hex) ]
Some clients require Base32 of info_hash (e.g., Vuze).
BitTorrent info hash v2 (BTMH)
BitTorrent v2 replaces the obsolete SHA-1 hash with a SHA-256 info hash. The v2 info-hash is given a new prefix (btmh) to allow for torrents that can participate in both v1 and v2 swarms [7]
xt=urn:btmh:[1220: (v2 prefix) BitTorrent Info Hash (Hex) ]
Message Digest 5 (MD5)
Supported by G2 (Gnutella2), such hashes are vulnerable to hash collision attacks.
xt=urn:md5:[ MD5 Hash (Hex) ]

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

"as" ("acceptable source")
Most clients treat "as" as equal to the "xs" token when it comes to priority, and ignore the timeout before contacting "as" sources denoted by the specs.
Content-Addressable Web URL
This type of RFC   2168-based link is used by gnutella as well as G2 applications. [8]
xs=http://[Client Address]:[Port of client]/uri-res/N2R?[ URN containing a file hash ]
xs=http://192.0.2.27:6346/uri-res/N2R?urn:sha1:FINYVGHENTHSMNDSQQYDNLPONVBZTICF
Link to a DirectConnect hub to find sources for a file
This type of 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 included link points, not to a client IP or direct source, but to a source cache which stores the IPs of other clients contacting it to download the same file. Once a client connects to the cache, it is served IPs for alternate sources, while its own IP is stored within the cache and forwarded to the next one connecting to the cache. 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]/

Supplement format (x.)

For experimental and self-complementing informal options, the prefix x. followed by a chosen suffix letter can be used. These names are guaranteed to never be standardized.

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

Clients

Client dn xl xt tr xs as kt mt ws
AMule YesYesurn:ed2k:NoUn­knownUn­knownUn­knownUn­knownUn­known
ApexDC++ YesYesurn:bitprint:
urn:tree:tiger:
Nodchub: [Note 1] dchub: [Note 1] NoNoUn­known
BitComet YesYesurn:btih:YesYes1.76NoNoNoYes1.74 [9]
Bitflu YesNourn:btih:YesNoNoNoNoUn­known
Deluge YesNourn:btih:YesNoNoNoNoUn­known
EiskaltDC++YesYesurn:tree:tiger:
urn:bitprint:
urn:btih: [Note 2]
urn:btmh: [Note 2]
Nodchub: [Note 1]
adc: [Note 3]
adcs: [Note 4]
dchub: [Note 1] YesNoUn­known
FlylinkDC++ YesYesurn:tree:tiger:
urn:bitprint:
urn:btih:
Nodchub: [Note 1]
adc: [Note 3]
adcs: [Note 4]
dchub: [Note 1] YesNoUn­known
gtk-gnutella YesYesurn:sha1:Nohttp:
push:
YesYesNoUn­known
KTorrent YesNourn:btih:YesNoNoNoNoUn­known
LimeWire YesYesurn:sha1:Nohttp:
urn:guid:
Un­knownNoNoUn­known
MonoTorrent YesYesurn:btih:YesNoYesNoNoUn­known
μTorrent YesNourn:btih:YesNoNoNoNoYes
qBittorrent YesNourn:btih:
urn:btmh:
YesUn­knownUn­knownNoNoUn­known
Shareaza YesYesurn:bitprint:
urn:btih:
urn:ed2k:
urn:md5:
urn:sha1:
urn:tree:tiger:
Yes [Note 5] http:
ftp:
http:
ftp:
(Same priority as xs)
YesNoUn­known
Tixati YesYesurn:btih:YesYesYesUn­knownUn­knownYes
Transmission [2] [10] YesNourn:btih:YesNoNoNoNoYes [11]
Vuze YesYesurn:btih:
urn:sha1:
YesYes5.7.5.0Yes5.7.5.0NoNoYes

See also

Explanatory notes

  1. 1 2 3 4 5 6 dchub://[hubaddress]:[hubport]
  2. 1 2 Passes link to external software
  3. 1 2 adc://[hubaddress]:[hubport]
  4. 1 2 adcs://[hubaddress]:[hubport]
  5. Since v2.5.1.0

Related Research Articles

Gnutella is a peer-to-peer network protocol. Founded in 2000, it was the first decentralized peer-to-peer network of its kind, leading to other, later networks adopting the model.

<span class="mw-page-title-main">Shareaza</span> Peer-to-peer file sharing application

Shareaza is a peer-to-peer file sharing client running under Microsoft Windows which supports the Gnutella, Gnutella2 (G2), eDonkey, BitTorrent, FTP, HTTP and HTTPS network protocols and handles magnet links, ed2k links, and the now deprecated gnutella and Piolet links. It is available in 30 languages.

eDonkey2000

eDonkey2000 was a peer-to-peer file sharing application developed by US company MetaMachine, using the Multisource File Transfer Protocol. It supported both the eDonkey2000 network and the Overnet network.

BitTorrent, also referred to as simply torrent, is a communication protocol for peer-to-peer file sharing (P2P), which enables users to distribute data and electronic files over the Internet in a decentralized manner. The protocol is developed and maintained by Rainberry, Inc., and was first released in 2001.

gtk-gnutella

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<span class="mw-page-title-main">Gnutella2</span>

Gnutella2, often referred to as G2, is a peer-to-peer protocol developed mainly by Michael Stokes and released in 2002.

In cryptography, Tiger is a cryptographic hash function designed by Ross Anderson and Eli Biham in 1995 for efficiency on 64-bit platforms. The size of a Tiger hash value is 192 bits. Truncated versions can be used for compatibility with protocols assuming a particular hash size. Unlike the SHA-2 family, no distinguishing initialization values are defined; they are simply prefixes of the full Tiger/192 hash value.

In cryptography, PBKDF1 and PBKDF2 are key derivation functions with a sliding computational cost, used to reduce vulnerability to brute-force attacks.

The eDonkey Network is a decentralized, mostly server-based, peer-to-peer file sharing network created in 2000 by US developers Jed McCaleb and Sam Yagan that is best suited to share big files among users, and to provide long term availability of files. Like most sharing networks, it is decentralized, as there is no central hub for the network; also, files are not stored on a central server but are exchanged directly between users based on the peer-to-peer principle.

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<span class="mw-page-title-main">Merkle tree</span> Type of data structure

In cryptography and computer science, a hash tree or Merkle tree is a tree in which every "leaf" node is labelled with the cryptographic hash of a data block, and every node that is not a leaf is labelled with the cryptographic hash of the labels of its child nodes. A hash tree allows efficient and secure verification of the contents of a large data structure. A hash tree is a generalization of a hash list and a hash chain.

<span class="mw-page-title-main">FrostWire</span> Free and open-source BitTorrent client

FrostWire is a free and open-source BitTorrent client first released in September 2004, as a fork of LimeWire. It was initially very similar to LimeWire in appearance and functionality, but over time developers added more features, including support for the BitTorrent protocol. In version 5, support for the Gnutella network was dropped entirely, and FrostWire became a BitTorrent-only client.

<span class="mw-page-title-main">Metalink</span> File format that describes one or more computer files available for download

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Peer-to-peer file sharing (P2P) systems like Gnutella, KaZaA, and eDonkey/eMule, have become extremely popular in recent years, with the estimated user population in the millions. An academic research paper analyzed Gnutella and eMule protocols and found weaknesses in the protocol; many of the issues found in these networks are fundamental and probably common on other P2P networks. Users of file sharing networks, such as eMule and Gnutella, are subject to monitoring of their activity. Clients may be tracked by IP address, DNS name, software version they use, files they share, queries they initiate, and queries they answer to. Clients may also share their private files to the network without notice due to inappropriate settings.

<span class="mw-page-title-main">Phex</span> Peer to peer file sharing client

Phex is a peer-to-peer file sharing client for the gnutella network, released under the terms of the GNU General Public License, so Phex is free software. Phex is based on Java SE 5.0 or later.

libtorrent

libtorrent is an open-source implementation of the BitTorrent protocol. It is written in and has its main library interface in C++. Its most notable features are support for Mainline DHT, IPv6, HTTP seeds and μTorrent's peer exchange. libtorrent uses Boost, specifically Boost.Asio to gain its platform independence. It is known to build on Windows and most Unix-like operating systems.

In the BitTorrent file distribution system, a torrent file or meta-info file is a computer file that contains metadata about files and folders to be distributed, and usually also a list of the network locations of trackers, which are computers that help participants in the system find each other and form efficient distribution groups called swarms. Torrent files are normally named with the extension .torrent.

References

  1. "BitTorrent v2". BitTorrent. Archived from the original on 30 October 2020. Retrieved 7 September 2020.
  2. 1 2 "magnet-test.c in trunk/libtransmission; Revision 9531". Transmission. Archived from the original on 2012-02-17. Retrieved 2012-02-04.
  3. 1 2 3 4 "BitTorrent Enhancement Proposal 9: Extension for Peers to Send Metadata Files". bittorrent.org (published 2008-01-31). 2017-03-26. Archived from the original on 2022-10-10. Retrieved 2022-11-04.
  4. "libtorrent/magnet_uri.cpp at 64817e0e8793d0875fc10245de52ffb2540a223d · arvidn/libtorrent". libtorrent. Archived from the original on 2022-11-04. Retrieved 2022-11-04 via GitHub.
  5. "BitTorrent Enhancement Proposal 53: Magnet URI extension - Select specific file indices for download". BitTorrent.org. 2017-06-06. Archived from the original on 2022-10-10. Retrieved 2022-11-04.
  6. "bep_0005.rst_post". bittorrent.org. Retrieved 2022-05-12.
  7. "BitTorrent v2". libbittorrent.org. libbittorrent. 2020-09-07. Archived from the original on 2022-10-22. Retrieved 2022-11-05.
  8. Chapweske, Justin (November 29, 2001). "HTTP Extensions for a Content-Addressable Web". www-talk. W3C. Archived from the original on July 28, 2011. Retrieved November 7, 2010.
  9. "v1.74 Core Improve: support ws parameter in Magnet URI, to add web seed". bitcomet. Archived from the original on 2021-04-10. Retrieved 2021-04-07.
  10. "magnet.c in trunk/libtransmission; Revision 9979". Transmission. Archived from the original on 2012-02-17. Retrieved 2012-02-04.
  11. "magnet.c in libtransmission: Commit 5c3fd1b5ccc3a8c4ab68e2c56861df31dd1c720a". Transmission. Archived from the original on 2021-09-04. Retrieved 2021-09-04.