inKey

inKey - small encryption utility with big encryption block (> 800 000 bit).

This program can protect very sensitive data, such e-mail, which has size up to 100 kilobytes, but processing speed might be too small with the bigger size of source data.

ProcessingTime(data) = O(data ^ 2);
USE IT ONLY TO PROTECT SMALL FILES (~ 100 Kb or a bit bigger).

You can use "PaperBack" to print your 100 Kb encrypted *.iK file to A4 paper and get strong encrypted digital letter.
https://sourceforge.net/projects/paperback

P.S. "inKey 6.0" encryption used in http://sourceforge.net/projects/absolutelysafechat/