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Authors:
James F. Kurose, Keith W. Ross
Chapter:
Security In Computer Networks
Exercise:
Problems
Question:13 | ISBN:9780132856201 | Edition: 6

Question

In the BitTorrent P2P file distribution protocol (see Chapter 2), the seed breaks the file into blocks, and the peers redistribute the blocks to each other. Without any protection, an attacker can easily wreak havoc in a torrent by masquerading as a benevolent peer and sending bogus blocks to a small sub- set of peers in the torrent. These unsuspecting peers then redistribute the bogus blocks to other peers, which in turn redistribute the bogus blocks to even more peers. Thus, it is critical for BitTorrent to have a mechanism that allows a peer to verify the integrity of a block, so that it doesn’t redistribute bogus blocks. Assume that when a peer joins a torrent, it initially gets a .torrent file from a fully trusted source. Describe a simple scheme that allows peers to verify the integrity of blocks.

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Answer

Refer the itTorrent P2P file distribution protocol (see Chapter 2) in the text book. Assume that when a peer joins a torrent, it initially gets a .torrent file from a fully trusted source.

The following a simple scheme that allows peers to verify the integrity of blocks:

  1. The MAC(Message Authentication Code) is used to each peer have the secret key‘s’ and compute the hash H (m+s)
  2. Assume a transmitting a block (m) and sent the message (m, h) to another peer. Then, hash h = H (m + s)
  3. If a peer receives a message (m, h), it should compute the hash H (m + s) and compare it with h=H (m+s).
    1. If the two hashes are same, then the peer accepts the blocks.
    2. If the two hashes are not same, then the peer rejects the blocks.
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