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== What's an ed2k hash? ==
In short, a hash is a checksum. It is used to detect errors in data by checking the integrity of the message/file. There are various different hash algorithms used for differing purposes, some that are focused more on security and some on speed. AniDB sports both kinds; CRC is not particularly secure at all, while MD5, SHA-1 and the MD4/ed2k hashes are much more secure from a cryptographic standpoint. They are not fail-safe though, but having more than one hash makes it exponentially harder to counterfeit a file. You might be able to fool one of the hashes, but generally not two, or as is the case with most of the files found in AniDB: four hashes!
In shortThe ed2k hash is based on the ''md4 algorithm'', but rather than providing a single hash is a checksum. It is used to detect errors in data by checking the integrity of the message/entire file. There are various different hash algorithms used for differing purposes, some that are focused more on security it breaks the file up into 9500kb ''chunks'' and some produces a final hash based on speedthe md4 sums of the chunks. AniDB sports both kinds; CRC While md4 is not particularly secure at all, while MD5, SHA-1 and the MD4/ed2k hashes are much more no longer considered secure from a cryptographic standpoint. They are not failsafe thoughperspective, but having for the purpose of uniquely identifying files it's more than one hash makes it exponentially harder to counterfeit a fileadequate. You might be able to fool one It is often listed as part of the hashesan ''ed2k link'', but generally not twowhich also includes a size in bytes, or as is the case with most of the files found in AniDB: four hashes!and a name.
The ed2k hash is based on the ''md4 algorithm'', but rather than providing a single hash of the entire file, it breaks the file up into 9500kb ''chunks'' and produces a final hash based on the md4 sums of the chunks. While md4 longer considered secure from a cryptographic perspective, for the purpose of uniquely identifying files it's more than adequate. It is often listed as part of an ''ed2k link'', which also includes a size in bytes, and a name. == Why does anidb AniDB require ed2k-hashes? == The main reason for this is that it avoids adding of double db database entries. AniDB will not allow you to add a file with the same ed2k-hash as an existing one.
The file size and ed2k-hash of a file is used to identify it globally.
== Why use ed2k instead of another type of hash? ==
 
* The combination of ed2k-hash and file size makes ed2k effective for uniquely identifying files.
* Since ed2k-hashes can be passed back and forth within a URI with both the hash and file size in a widely recognized format it is a convenient method for adding or checking files.
== Which software can be used to generate them? ==
 
If you have the file(s) on your hard disk or on CD you can use all kinds of tools to generate the ed2k-hash and other additional info:
* [[AvdumpAvdump2]] is the preferred tool as it can automatically creq files.* [[AniDB_OAniDB O'Matic]] by BennieB/PetriW can generate ed2k-hashes. It generates ed2k-hashes, md5, sha-1, crc32 in one go and also lists stuff like codec, resolution, bitrates, ...* [http://ed2k-tools.sourceforge.net/projects/ed2k-tools/ index.shtml ed2k_hash] another tool which is commandline based (current Windows and OSX versions have a GUI as well) and also available for Unix operating systems (Linux/BSD/etc).* [http://malich.content.no-ip.org/filehash/filehash-0.5.3.zip Filehash] a little java Java program written by Malich. for For further info on it read [http://forum.anidb.net/viewtopic.php?t={{OldThreadLink|77 |here]}}
* [http://www.slavasoft.com/hashcalc/ Hashcalc] can create md5, sha-1, crc32, ed2k-hashes and various other hashes in 1 go.
* [http://rhash.anz.ru/ RHash] multiplatform open source console utility for computing md5/sha1/crc32 hashes, EDonkey and Magnet links for a directory tree.
== How is an ed2k hash calculated exactly? ==
 
A file is hashed in 9728000 byte ''chunks'', using the md4 algorithm, and produces a 128 bit hash for each chunk. For files with only one chunk, the ed2k hash ''is'' the md4 of the file, however for hashes with 2 or more chunks the the hash of each chunk is appended to those before it, and an further md4 of the hashes themselves provides the ed2k hash of the file. Pseudo code is given below:
:if filesize is less than <font color="{{colour|blue">|or equal to</font> }} 9728000:
:: return md4 of file
:for chunk of size upto 9728000 in file:
:: append md4 of chunk to hashlist
:<font color="{{colour|red">|if filesize is a multiple of 9728000:}}::{{colour|red|append md4 of null to hashlist</font>}}
:return md4 of hashlist
Note that there are two different ways in practice that implimentations implementations treat the 9728000 byte boundary, given as either the red code or the blue code above, black is common to both. In practice this difference only affects a tiny number of files, however is the one case where two 'valid' ed2k hashes might be produced from one file. See forum topic [http://forum.anidb.net/viewtopic.php?t=1187 1] on this issue as well.
=== List of which clients use which method ===
[[Avdump2]] uses both methods. It will creq files from blue to red and store blue in file description ({{AniDBShortLink|f7047|Alternative ed2k}}).*<font color="{{colour|blue">|edonkey2000 v0.5.0 to v1.4.3</font>}}*<font color="{{colour|blue">|mldonkey (2.5.30.17 tested)</font>}}*<font color="{{colour|blue">|shareaza (1.8 tested)</font>}}*<font color="{{colour|blue">|HashCalc Version (2.01 tested)</font>}}*<font color="{{colour|blue">|edonkey-tool-hash (0.4.0 tested)</font>}}*<font color="{{colour|blue">|fsum (2.51 tested)</font>}}*<font color="{{colour|blue">|ed2k_hash (0.4.0 tested)</font>}}*<font color="{{colour|blue">|hashgen (0.0.6 tested)</font>}}*<font color="{{colour|red">|edonkey2000 until v0.5.0</font>}}*<font color="{{colour|red">|emule (0.46c tested)</font>}}*<font color="{{colour|red">|AOM (0.5.5.239 tested)</font>}}*<font color="{{colour|red">|webaom (v1.13 tested)</font>}}*<font color="{{colour|red">|ed2k code by Stephane D'Alu (1.4 tested)</font>}}*{{colour|red|jacksum (1.7.0 tested)}}*{{colour|red|rhash (1.1.9 tested)}}
=== List of affected files, by fileID ===
 
{| style="font-family: monospace; text-align: right; margin: auto;"
! style="font-family: sans-serif; text-align: center;" | File
|File of zeros || 19456000 || 194ee9e4fa79b2ee9f8829284c466051 || 114b21c63a74b6ca922291a11177dd5c
|- style="background-color: #eee;"
|http://anidb.infonet/f7047 || 145920000 || 1c2b1a6b142955d84af5d3210d3ece6f || 4f79548623c6099896a489257163764e
|-
|http://anidb.infonet/f24359 || 136192000 || f869547f07275eda0067694540c9dc93 || df294338b38a29f81ad84f1f364b4504
|- style="background-color: #eee;"
|http://anidb.infonet/f31383 || 136192000 || f869547f07275eda0067694540c9dc93 || df294338b38a29f81ad84f1f364b4504
|-
|http://anidb.infonet/f48530 || 175104000 || a641926fa474fafe3f2c12676ea66b8e || c110c2b684aaa391a980bde4e6ee9f1f
|- style="background-color: #eee;"
|http://anidb.infonet/f51131 || 107008000 || 5911beead79e0fa9043baee70683ef56 || aa399ff3a0ab9f8eb939dbcd7b7d0ec3
|-
|http://anidb.infonet/f51330 || 175104000 || fa7fbadaed151b003032985eae5c3420 || 148b2cf54cb4d66f70939ec5224d7961
|- style="background-color: #eee;"
|http://anidb.infonet/f55744 || 97280000 || 4c8a9540fe5aa2f4d9f8cac835a071a6 || 2fcd55bdeae2a92cc99d70763a64f048
|-
|http://anidb.infonet/f56411 || 165376000 || b7b2f5eaea94bf89f5e03a775d9d9478 || f498072c0849cee180e4a1a7d34a26d2
|- style="background-color: #eee;"
|http://anidb.infonet/f57766 || 145920000 || 7a54eda5d89ed525974487aa94515701 || 85d995b678284e7db5d52df1375971a9
|-
|http://anidb.infonet/f73921 || 184832000 || f8fdbb017cd74ff66882a7c6f33fae24 || fc9210c307f99ed7339556d5f05f3d59
|- style="background-color: #eee;"
|http://anidb.infonet/f78552 || 194560000 || 8f1fb4062cd1e8f578013e9b7719d05a || f93db3a2ed31e7f48fe35945e4c5c6e8
|-
|http://anidb.infonet/f80216 || 165376000 || d61b705c59199666e164a274e7f91bec || ddcec8fdcddd43276a2c173498345789
|- style="background-color: #eee;"
|http://anidb.infonet/f92884 || 68096000 || c310997efade26c107e44036c1fd0dc3 || b83bdad42c5ae5204bea3a25959e2180
|-
|http://anidb.infonet/f123554 || 243200000 || 822fc0f338fe8e43d96b9a99fe9632ce || ee3557fe68ccd056302710a185f4445f
|- style="background-color: #eee;"
|http://anidb.infonet/f126410 || 184832000 || e19581a5518a11fbd50c1f23f9c21b95 || 87ac7a62de204473d3f5448214f4207c
|-
|http://anidb.infonet/f130233 || 184832000 || 91ae6f6b3bb42e0792c63efb9f1aa81e || 8ad09e1b46b695ebae0243b1856e801c
|- style="background-color: #eee;"
|http://anidb.infonet/f142402 || 155648000 || || 4538e1fded9d7661e1ad7d56e7406054
|-
|http://anidb.infonet/f165143 || 165376000 || 0ced631bb9010d3ccd331689a2fb02de || 6a092c056bc46e7a08d63408f918ba52
|- style="background-color: #eee;"
|http://anidb.infonet/f166304 || 184832000 || aab2ce19d5b786af20d6e4a15f63552f || aa9930ccd300a2feac30b0e49830c321
|-
|http://anidb.infonet/f174421 || 223744000 || cd87540a7b48e87e78e7c714fbf7581e || a7c9a857b6d584bae0568495b92ea609|- style="background-color: #eee;"|http://anidb.net/f200233 || 58368000 || cfff67163f6ca9bbed26211e140b10e1 || 0943c164b8a076c88551f0b2c1757436
|-
|http://anidb.info/f200233 || 58368000 || cfff67163f6ca9bbed26211e140b10e1 || 0943c164b8a076c88551f0b2c1757436|-|http://anidb.infonet/f220069 || 389120000 || a182915f5cd114937f760246da92234b || 43324839e08afca1d83a890468f87f5e|-style="background-color: #eee;"|http://anidb.infonet/f240925 || 126464000 || bae493f413037066ce5a597be4d97e8f || 725a209cf70715b3fdfb03348bb040c6
|-
|http://anidb.infonet/f243620 || 311296000 || 8d81479f7b5ba92c3094630899b5ec7a || 1cc497d5f73d9365e88dcdaa4207559e
|}
==See also==*[[Export ED2K Links]][[Category: Definitions]][[Category: Guidelines]]

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