REM *** By changing the key and pattern, an encryption system that is difficult to break can be achieved. ***

text$ = "You are encouraged to solve this task according to the task description, using any language you may know."
key$ = "desoxirribonucleic acid" // With a single character you get a Caesar encryption. With more characters the key is much more difficult to discover.
CIPHER = 1 : DECIPHER = -1

print text$ : print
encrypted$ = criptex$(text$, key$, CIPHER)
a = open("cryptedText.txt", "w") : if a then print #a encrypted$ : close #a end if
print encrypted$ : print
print criptex$(encrypted$, key$, DECIPHER)

sub criptex$(text$, key$, mode)
	local i, k, delta, longtext, longPattern, longkey, pattern$, res$
	
	pattern$ = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890 .,;:()-"
	
	longPattern = len(pattern$)
	longtext = len(text$)
	longkey = len(key$)
	
	for i = 1 to longtext
		k = k + 1 : if k > longkey k = 1
		delta = instr(pattern$, mid$(text$, i, 1))
		delta = delta + (mode * instr(pattern$, mid$(key$, k, 1)))
		if delta > longPattern then
			delta = delta - longPattern
		elseif delta < 1 then
			delta = longPattern + delta
		end if
		res$ = res$ + mid$(pattern$, delta, 1)
	next i

	return res$
end sub