making an encryption, decryption key in max

Hello
I write a journal in apple textedit, and I was hoping to create a simple homemade encryption/decryption key for it using max.
It's not terribly sensitive, I don't need military grade encryption but I thought it would fun to play with.
Ideally I'd like to make a patch that takes my .rtf file, scrambles it, saves it as an unopenable corrupted file, then imports it, and puts the data back in the right place.

I see that I can use the filein object to read my rtf file as binary data. Is there any way I could re export that binary data and change the file extension to rtf to have a readable rtf file thats identical to my original? If this were possible, I could scramble and unscramble the binary data to do my encryption

I've tried putting the binary data into a very long itable then saving from that, but that doesnt seem to work

thanks very much!