We have a program that encrypts files in some unknown way. A good first step is to give it a repeated pattern and see what it outputs:
> python -c 'print "A" * 50' > /tmp/abc
> ./encrypt6 /tmp/abc /tmp/out
> cat /tmp/out
EICTDGYIYZKTHNSIRFXYCPFUEOCKRNEICTDGYIYZKTHNSIRFXY