One (hopefully helpful) piece of information is that this tool didn't take long to encrypt plethora of files in one data holding partition on my hard drive. No matter if the files were large or small, it successfully encrypted all of them. It kept only one CPU core busy on my machine. Perhaps this can help identify the cipher or method used for encryption
This also suggests that a relatively small length key pair was used to do encryption. Meaning around or under 2K bit key. I wonder if this info helps.
The speed with which files were encrypted suggests use of a simpler method. Just that finding or guessing or brute forcing RSA key pair is the pickle.