Learn in the textbookFundamentals of Encryption and Cipher Methods
DefinitionA hash function (ハッシュ関数) derives a fixed-length value, the hash value (ハッシュ値), from data of any length, and the original data cannot be worked out from the hash value.
ExplanationEven a tiny change in the input changes the hash value drastically. Thanks to this, you can check whether two pieces of data are identical by comparing their short hash values instead of the data itself. SHA-256 is a typical example.
AnalogyIt is like taking a fingerprint of a document. The same document always leaves the same print, but the print cannot tell you what the document says.
Memory hookThe English word hash means to chop finely, as in hash browns. Once chopped, nothing goes back to its original shape.