A way for separate companies to match their data sets without either side being able to access the other’s data. A ‘hashing algorithm’ is a one-way mathematical function that creates a non-reversible fingerprint for a piece of text. If the same hashing algorithm is used against a piece of text, it will always produce the same “message digest” – basically a fingerprint of the original data. No mathematical function or “key” exists to reverse this fingerprint back to the original value. So, for example, if two computers both hash ‘firstname.lastname@example.org’, both will end up with a fingerprint like 7f759ccc0f730cbdb4e297010b8ec5e5’. However, given the fingerprint ‘7f759ccc0f730cbdb4e297010b8ec5e5’, there is no mathematical function to reverse that back to ‘email@example.com’.