It’s a cryptographic hash function, it basically assigns a unique but seemingly random number to anything you give the function
so for example you can take the sha 256 of a program and if someone has the same number it means they have the same program without sending everything
SHA 1 the secure hash algorithm version 1, generated a 160 bit number, however it’s pretty old and people have figured out that it is possible to trick it and forge a file that has the same sha1 as another file, which means it’s not as secure
SHA 256 generates a 256 bit number and it’s considered very secure and basically impossible to tamper with
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