Swarm Integrity: Chunk-Hash Verification in P2P File Sharing

Swarm Composition

Malicious peer share 25%

Quarantine threshold (bad chunks) 2

Request rate 3/s

Download Status

0 / 32 chunks0%

Peers quarantined

Chunks rejected

Corrupted & accepted

Swarm trust score

100%

How it works

A shared file is split into fixed-size chunks. Whoever publishes it also publishes a trusted manifest: one cryptographic hash per chunk, computed once from the genuine data (this is exactly what a BitTorrent .torrent piece-hash list or an IPFS/Merkle-DAG CID does).

hash = H(chunk_bytes)
accept chunk  ⟺  H(received_bytes) == manifest[i]

This simulator runs a real 32-bit FNV-1a hash over each chunk's simulated content. A malicious or faulty peer serves tampered bytes; because a cryptographic-style hash has the avalanche property, a single changed byte produces a completely different digest — there is no partial match to exploit.

Verification ON — every incoming chunk is hashed and compared against the manifest before being accepted into the file. A mismatch is rejected, logged, and counted against that peer.
Quarantine threshold — once a peer's rejected-chunk count reaches this value, the swarm blacklists it: no further requests are routed there, exactly like a real client's peer-banning logic.
Verification OFF — chunks are accepted on receipt with no check, showing why an unverified transfer lets a single bad peer silently corrupt the reassembled file.
Swarm trust score — the share of currently-active peers that have never failed a check, a simple proxy for the reputation systems real swarms use to prefer known-good sources.

Real-world relevance: this is the defensive backbone of every content-addressed or piece-verified distribution system — BitTorrent, IPFS, package-manager mirrors, and CDN edge caches all reject bytes whose hash doesn't match a signed manifest before trusting them.

You (downloader) Trusted peer Malicious (undetected) Quarantined

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