Программа шифровки:
DATA "ауоыэяюёие"
DATA "бвгджзклмнпрстфхцчшщ"
DATA "ъйь"
DIM s10 AS STRING, s20 AS STRING, s3 AS STRING
DIM i AS INTEGER
DIM s AS STRING, t AS STRING
CLS
READ s10, s20, s3
RANDOMIZE TIMER
INPUT "Введите фразу: ", s
t = ""
FOR i = 1 TO LEN(s)
   t = t + MID$(s, i, 1)
   t = t + MID$(s10, INT(10 * RND + 1), 1)
   t = t + MID$(s20, INT(20 * RND + 1), 1)
   t = t + MID$(s3, INT(3 * RND + 1), 1)
NEXT i
PRINT t
END

Программа дешифровки:
DIM s AS STRING, t AS STRING, i AS INTEGER
CLS
INPUT "Введите фразу: ", s
t = ""
FOR i = 1 TO LEN(s) STEP 4
   t = t + MID$(s, i, 1)
NEXT i
PRINT t
END