For when you need to e-mail a sensitive information or safely store a file somewhere, use encryption.
Most encryption/decryption requires dedicated tools, for which the source code may or may not be available, which may be available on Microsoft, but not Apple, or vice versa.
There is a simple solution: OpenSSL. Trusted open source, available on almost all architectures.
openssl enc -aes-256-cbc -e -base64 -salt -in FILENAME -out FILENAME_CRYPTED.asc
openssl enc -aes-256-cbc -d -base64 -salt -in FILENAME_CRYPTED.asc -out ORIGINAL_FILENAME
If you are working with text, i.e. secrets in e-mails/chat, you need “base64”. It’ll make the file bigger, but safe to copy-and-paste.
If you are simply storing files on disk, they can stay binary and file size may matter more, so leave out the “base64”.