It sounds to me to be an obvious difference between your invention and the prior art. I am of ordinary skill in the arts of programming and encryption and ASCII vs. Hexadecimal is an obvious difference:
These are the examiners guidelines in regard to obviousness:
A quote from this reference:
(a) A patent may not be obtained though the invention is not identically disclosed or described as set forth in section 102, if the differences between the subject matter sought to be patented and the prior art are such that the subject matter as a whole would have been obvious at the time the invention was made to a person having ordinary skill in the art to which said subject matter pertains. Patentability shall not be negatived by the manner in which the invention was made.
A patent would not be issued and even if it was not considered obvious by an examiner you would have freedom to operate problems from the previous cited patent. You would likely have to license the previous patent to practice your hypothetical patent.
However your listed patent only mentions encryption as one of the dozens of non-patent references. So it seems to be a moot question.