I take it you haven’t studied encryption.
I don’t think any encryption algorithm is safe against a multi-million dollar supercomputer array system designed to crack encrypted files.
I don’t know what the dollar value is of the most advance technology the government current employs, but I know there are massively arrayed super-fast computers dedicated to breaking encryption. I doubt anything this guy used would be safe. Especially, since the story says he handed the key out to several people. There is no such thing as a secret if two if more than one person knows.