Entropi Designed to securely encrypt small to medium sized text files, with a lower bound estimate, of approximately 200,000 characters. Much larger amounts of data can probably still be encrypted with impunity, although it is not clear to me whether a longer encryption will be any easier to crack. If anything: it will probably make analysis attempts more tedious. Employing a larger substitution alphabet would increase the lower bound exponentially, but then the process will take a bit longer