Hash list

Before downloading a file on a p2p network, in most cases the top hash is acquired from a trusted source, for instance a friend or a web site that is known to have good recommendations of files to download.

Hash lists can be used to protect any kind of data stored, handled and transferred in and between computers.

An important use of hash lists is to make sure that data blocks received from other peers in a peer-to-peer network are received undamaged and unaltered, and to check that the other peers do not "lie" and send fake blocks.

If the hash list only needs to protect against unintentional damage unsecured checksums such as CRCs can be used.

[citation needed] Hash lists are better than a simple hash of the entire file since, in the case of a data block being damaged, this is noticed, and only the damaged block needs to be redownloaded.