/*
**  Usage:
**      out = cipher(in, key, mode);
**
**  Arguments:
**      in      input, string
**      key     enciphering key, string
**      mode    0 = decipher, 1 = encipher
**
**  Returns:
**      out     a string, deciphered or enciphered using
**              a simple Vigenere style cipher
**
**  copyright (c) 2006, John Leffingwell
**  www.planetxot.com
*/
var in, key, mode, out;
in = argument0;
key = argument1;
mode = argument2;
out = "";
var inLen, keyLen, pos, inChar, keyChar, outChar;
var inVal, keyVal, outVal;
inLen = string_length(in);
keyLen = string_length(key);
for (pos = 0; pos < inLen; pos += 1) {
    inChar = string_char_at(in, pos + 1);
    keyChar = string_char_at(key, (pos mod keyLen) + 1);
    inVal = ord(inChar);
    keyVal = ord(keyChar);
    if (mode) {
        outVal = (inVal + keyVal) mod 256;
    }else{
        outVal = (256 + inVal - keyVal) mod 256;
    }
    outChar = chr(outVal);
    out = out + outChar;
}
return out;