密钥可以通过给定参数更改，且该参数随加密了的信息一起发送，并在阅读（需要权限）时自动插入“锁孔”。需要说明的是，密钥由参数唯一确定，但只截获参数，即使在理论上也无法算出密钥！故收发信息的双方自始至终无人知道真正的密钥是什么。


[em12]


REM code and uncode
choice: PRINT "to code, press 1"
PRINT "to uncode, press 2"
PRINT "to clear the screen, type CLS"
PRINT "to exit, type sy"
PRINT
INPUT "i want to ", c$
IF c$ = "sy" THEN END
IF c$ = "cls" THEN CLS
IF c$ = "1" THEN GOTO code
IF c$ = "2" THEN GOTO uncode ELSE GOTO choice

code: FOR x = 1 TO 2 STEP 0
PRINT
INPUT "text to be code:", text$
LET cd = LEN(text$)
IF text$ = "sy" THEN END
IF text$ = "ws" THEN GOTO choice
q = 1
FOR i = 1 TO cd STEP 1
LET zm$ = MID$(text$, i, 1)
LET zmasc = ASC(zm$)
zmasc = zmasc + q
LET zmhy$ = CHR$(zmasc)
PRINT zmhy$;
q = q + 1
IF q = 4 THEN q = 1
NEXT i
NEXT x
END


uncode: FOR x = 1 TO 2 STEP 0
PRINT
INPUT "text to be uncode:", text$
LET cd = LEN(text$)
IF text$ = "sy" THEN END
IF text$ = "ws" THEN GOTO choice
q = 1
FOR i = 1 TO cd STEP 1
LET zm$ = MID$(text$, i, 1)
LET zmasc = ASC(zm$)
zmasc = zmasc - q
LET zmhy$ = CHR$(zmasc)
PRINT zmhy$;
q = q + 1
IF q = 4 THEN q = 1
NEXT i
NEXT x
END

以上是简略版，不含对密钥的更改，但只需再加入一个input 语句就可解决问题。