CODEWITHSUNDEEP
bittorrentmonotorrent
LOST
LOST

Reputation: 3284

Is it possible to get hashes of individual 16KB blocks from a v2 torrent file? v1?

I want to cache torrent blocks based on their content hash. In v2 instead of simple block hashes there's a merkle tree, whose exact composition I can't quite comprehend.

I am working with MonoTorrent library, and it has IPieceHashes.GetHash(hashIndex) function where hashIndex varies from from 0 to piece count - 1. But there's no similar function to get hash of individual blocks (in case piece consists of multiple blocks).

Upvotes: 0

Views: 105

Answers (1)

the8472
the8472

Reputation: 43125

In v2 the easiest way to obtain them is to download a whole piece instead of a chunk, compute the leaf hashes from the data you have received and then verify the leaf hashes against the piece layers in the .torrent metadata file.
Alternatively you can hash request the leaf hashes while downloading chunks from a peer and verify them against the file root.
Both approaches involve merkle tree verification.

In v1 you're limited to downloading a whole piece and verifying its hash against the pieces list in the metadata file.

Upvotes: -1

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