Procedure.s CC_encrypt(plainText.s, key, reverse = 0)
  ;if reverse <> 0 then reverse the encryption (decrypt)
  If reverse: reverse = 26: key = 26 - key: EndIf

  Static alphabet$ = "ABCEFGHIJKLMNOPQRSTUVWXYZABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyz"

  Protected result.s, i, length = Len(plainText), letter.s, legal
  If key < 1 Or key > 25: ProcedureReturn: EndIf  ;keep key in range

  For i = 1 To length
    letter = Mid(plainText, i, 1)
    legal = FindString(alphabet$, letter, 1 + reverse)
    If legal
      result + Mid(alphabet$, legal + key, 1)
    Else
      result + letter
    EndIf
  Next
  ProcedureReturn result
EndProcedure

Procedure.s CC_decrypt(cypherText.s, key)
  ProcedureReturn CC_encrypt(cypherText, key, 1)
EndProcedure

If OpenConsole()
  Define key, plainText.s, encryptedText.s, decryptedText.s

  key = Random(24) + 1 ;get a random key in the range 1 -> 25

  plainText = "The quick brown fox jumped over the lazy dogs.": PrintN(RSet("Plain text = ", 17) + #DQUOTE$ + plainText + #DQUOTE$)
  encryptedText = CC_encrypt(plainText, key): PrintN(RSet("Encrypted text = ", 17) + #DQUOTE$ + encryptedText + #DQUOTE$)
  decryptedText = CC_decrypt(encryptedText, key): PrintN(RSet("Decrypted text = ", 17) + #DQUOTE$ + decryptedText + #DQUOTE$)

  Print(#CRLF$ + #CRLF$ + "Press ENTER to exit"): Input()
  CloseConsole()
EndIf