Ed2k-hash

What's an ed2k hash?

A hash is a <insert non-laziness here>

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 no 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 require ed2k-hashes?

The main reason for this is that it avoids adding of double db 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.

You are allowed to add files without ed2k-hashes to AniDB, however you should edit those files later and add the missing ed2k-hashes. Once you added a certain number of files without ed2k-hashes you may no longer add new files without ed2k-hashes until you edit your old files first.

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 URL with both the hash and file size in a widely recognized format it is a convenient method for adding or checking files.
Other hashes are good for validating if a file is corrupt if you already know what file you are comparing it against, but cannot necessarily globally identify a file in the system like the ed2k.
AniDB was designed around ed2k, although other hashes have been added to the file records for validation, the internal structure is based on ed2k. If the site goes through a complete redesign then maybe another hash will be made the primary hash, but at this point, this is not likely to change.

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:

AniDB_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, ...
ed2k_hash another tool which is commandline based and also available for Linux.
Filehash a little java program written by Malich. for further info on it read here
Hashcalc can create md5, sha-1, crc32, ed2k-hashes and various other hashes in 1 go. though at least 1 case is known in which it created a wrong ed2k!

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 or equal to 9728000:

return md4 of file

for chunk of size upto 9728000 in file:

append md4 of chunk to hashlist

if filesize is a multiple of 9728000:

append md4 of null to hashlist

return md4 of hashlist

Note that there are two different ways in practice that implimentations 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.

edonkey2000 v1.4.3
mldonkey-2.5.30.17
HashCalc Version 2.01
edonkey-tool-hash-0.4.0
fsum 2.51
ed2k_hash 0.4.0
emule 0.46c
AOM 0.5.5.239
webaom v1.13
ed2k (Stephane D'Alu) 1.4

File	Size (bytes)	Blue method	Red method
File of zeros	9728000	d7def262a127cd79096a108e7a9fc138	fc21d9af828f92a8df64beac3357425d
File of zeros	19456000	194ee9e4fa79b2ee9f8829284c466051	114b21c63a74b6ca922291a11177dd5c
http://anidb.info/f7047	145920000	1c2b1a6b142955d84af5d3210d3ece6f	4f79548623c6099896a489257163764e
http://anidb.info/f24359	136192000	f869547f07275eda0067694540c9dc93	df294338b38a29f81ad84f1f364b4504
http://anidb.info/f31383	136192000	f869547f07275eda0067694540c9dc93	df294338b38a29f81ad84f1f364b4504
http://anidb.info/f48530	175104000	a641926fa474fafe3f2c12676ea66b8e	c110c2b684aaa391a980bde4e6ee9f1f
http://anidb.info/f51131	107008000		aa399ff3a0ab9f8eb939dbcd7b7d0ec3
http://anidb.info/f51330	175104000	fa7fbadaed151b003032985eae5c3420	148b2cf54cb4d66f70939ec5224d7961
http://anidb.info/f55744	97280000	4c8a9540fe5aa2f4d9f8cac835a071a6	2fcd55bdeae2a92cc99d70763a64f048
http://anidb.info/f56411	165376000	b7b2f5eaea94bf89f5e03a775d9d9478	f498072c0849cee180e4a1a7d34a26d2
http://anidb.info/f57766	145920000	7a54eda5d89ed525974487aa94515701	85d995b678284e7db5d52df1375971a9
http://anidb.info/f73921	184832000	f8fdbb017cd74ff66882a7c6f33fae24	fc9210c307f99ed7339556d5f05f3d59
http://anidb.info/f78552	194560000	8f1fb4062cd1e8f578013e9b7719d05a	f93db3a2ed31e7f48fe35945e4c5c6e8
http://anidb.info/f80216	165376000	d61b705c59199666e164a274e7f91bec	ddcec8fdcddd43276a2c173498345789
http://anidb.info/f92884	68096000	c310997efade26c107e44036c1fd0dc3	b83bdad42c5ae5204bea3a25959e2180
http://anidb.info/f123554	243200000	822fc0f338fe8e43d96b9a99fe9632ce	ee3557fe68ccd056302710a185f4445f
http://anidb.info/f126410	184832000	e19581a5518a11fbd50c1f23f9c21b95	87ac7a62de204473d3f5448214f4207c
http://anidb.info/f130233	184832000	91ae6f6b3bb42e0792c63efb9f1aa81e	8ad09e1b46b695ebae0243b1856e801c
http://anidb.info/f142402	155648000		4538e1fded9d7661e1ad7d56e7406054
http://anidb.info/f165143	165376000	0ced631bb9010d3ccd331689a2fb02de	6a092c056bc46e7a08d63408f918ba52
http://anidb.info/f166304	184832000	aab2ce19d5b786af20d6e4a15f63552f	aa9930ccd300a2feac30b0e49830c321
http://anidb.info/f174421	223744000	cd87540a7b48e87e78e7c714fbf7581e	a7c9a857b6d584bae0568495b92ea609