what kind of hash is the `filehash` in torrent file?

[CHNan]

I've found some torrents with 'filehash' property on each file. No idea what hash is that?

[The UnUsual Suspect]

from the most recent published bittorrent specifications

info_hash The 20 byte sha1 hash of the bencoded form of the info value from the metainfo file. Note that this is a substring of the metainfo file. The info-hash must be the hash of the encoded form as found in the .torrent file, regardless of it being invalid. This value will almost certainly have to be escaped.

More info on SHA-1 hash can be found Here

[CHNan]

from the most recent published bittorrent specifications

info_hash The 20 byte sha1 hash of the bencoded form of the info value from the metainfo file. Note that this is a substring of the metainfo file. The info-hash must be the hash of the encoded form as found in the .torrent file, regardless of it being invalid. This value will almost certainly have to be escaped.

More info on SHA-1 hash can be found Here

It is not the usual infohash of a torrent file. It`s some kind of hash of the file that will be uploaded. If the file is less than 10M, the filehash`s value is the same as the file`s sha1 hash. While the file is lager than 10M, it`s otherwise.

[The UnUsual Suspect]

ok, that sounds like the LTseed hash, it's used to look for that file from alternate sources such as other torrents, http/ftp servers or eMule sources. If the torrent is authored with bitcomet and LTseed is enabled, each file will have this hash, otherwise it will be uploaded by the first bitcomet peer that completes the download (assuming LTseed option is enabled).

This can be very helpful not only to other bitcomet peers but the entire swarm in cases where some of the data isn't available from the bittorrent swarm, then the bitcomet peer can download the data elsewhere, complete the download and become a seeder to help the rest of the bittorrent swarm to complete the download.

[CHNan]

ok, that sounds like the LTseed hash, it's used to look for that file from alternate sources such as other torrents, http/ftp servers or eMule sources. If the torrent is authored with bitcomet and LTseed is enabled, each file will have this hash, otherwise it will be uploaded by the first bitcomet peer that completes the download (assuming LTseed option is enabled).

This can be very helpful not only to other bitcomet peers but the entire swarm in cases where some of the data isn't available from the bittorrent swarm, then the bitcomet peer can download the data elsewhere, complete the download and become a seeder to help the rest of the bittorrent swarm to complete the download.

Thanks. I found what you illuminated in http://wiki.bitcomet.com/long-term_seeding.

I just wonder what kind of hash this LT-hash is, and how it is calculated.

[The UnUsual Suspect]

LTseeding protocol is proprietary property belonging to the BitComet Development team. We've published the basics on how it works and what it does as part of bitcomet's documentation, but anything further could only be provided by the development team directly.