Often it is necessary to verify that data, once it has been sent, it has got through to its destination intact. A good way of ensuring data security protocols and tactical communication is to calculate a ‘hash’ of the data that is sent, then to calculate a hash of what is received, and make sure that the hashes are the same. 

​

A hash is a single number or string of characters, of a fixed length, that is a unique function of the document contents. For example, imagine a document painted onto a pane of glass, with each letter of the alphabet having its own colour – then washing the paint off the glass into a bucket and mixing the colours together. The colour you’d get is exactly like a hash: you cannot reconstruct the document from it, yet it is unique to the document – changing one letter of the document would cause the final colour to be subtly different.

​

A blockchain is an extreme version of a hash to ensure secure data transfer – in fact a table of hashes which are themselves hashed together and the results copied widely to everyone who has an interest in the data. No link in the chain of hashes can be altered without disrupting the whole chain, giving an extremely secure, auditable and immutable record of all the data transfers.