Hashing

Hashing is a basic tool of computer security

Any amount of data goes in; a fixed-size checksum (*'hash'*) comes out

The algorithm is very carefully designed:

Different inputs produce different outputs

If inputs match, checksums match, if checksums differ, inputs differ (obvious)

If inputs differ, checksums differ, if checksums match, inputs match (not obvious)

Very difficult to produce two inputs with the same output

Very difficult to produce a desired target checksum

Small changes in the input produce drastic changes in the output