Compression nearly suffices as a sort of crude (not secure) cryptography. Compression algorithms use mathematical formulas along with a table (or crosswalk/dictionary) to substitute for characters and their positions throughout an original text.

When you decompress a file, the computer uses that table in combination with the generated formulas in reverse to restore an originfal text.

-- ---- 

When you decompress a file, the computer uses that table in combination with the generated formulas in reverse to restore an original text.