Election Glossary

We provide explanations and background information on elections, voting rights and digital democracy

Block Checksums

Block checksums are used to check the integrity of data as it is transmitted or stored.

Use of block checksums in POLYAS online voting systems 

In online voting a block checksum is used to check ballots which have been cast. The input ballots are sorted into blocks and have their own block checksum. Each new block is built on the basis of the previous block. The ballots inside each single block are sorted according to random classifications. These classifications ensure that no individual ballot can be linked back to the time at which it was cast, nor can the identity of the voter be deduced.  Block checksums are built on the basis of a single, collective checksum for the election as a whole.

Checking online ballot box vote-count with the help of block checksums

Block checksums serve the additional purpose of helping to verify the accuracy of vote-counting. They do this alongside the checksum for the election as a whole. Any recount of the ballot box data must match the block checksums in order and value. If they do, then the election result is verified.

Click here for further information on verifying online election results using an independent tool.

See also: Online voting, data security, IT security

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