I don't have a handy place to stash 5MB of data publicly, but you can run the following in SBCL (or the equivalent in whatever language you prefer): (in-pa

I don't have a handy place to stash 5MB of data publicly, but you can run the following in SBCL (or the equivalent in whatever language you prefer): (in-package :cl-user) (use-package :ironclad) (let ((data (make-array (* 5 1024 1024) :element-type '(unsigned-byte 8) :initial-element (char-code #\X)))) (encrypt-in-place (make-cipher :aes :key (sb-ext:string-to-octets "YELLOW SUBMARINE") :mode :ctr :initialization-vector (make-array 16 :element-type '(unsigned-byte 8))) data) (with-open-file (tmp "/tmp/data" :direction :output :element-type '(unsigned-byte 8)) (write-sequence data tmp))) That's a file of 5,242,880 'X' characters, encrypted with the key 'YELLOW SUBMARINE' and an all-zero initialization vector. You will not be able to compress it.