Okay, taken this about as far as I can without revealing some work-related
stuff. This is realted to the 'mHash' thread elsewhere.

A little string substitution cipher called 'mCrypt' (Mike's Crypt) below...

Couple of quick additional notes:

.. substitution ciphers have a surface area of attack that are prone to
frequency analysis, so the astute user will use a long password, or better
yet a 'passphrase'. Song lyrics are easy to remember, eg:

passphrase: 'We all live in a yellow Subm@rine321"

.. error-checking is your baby, here's its handled in advance, be sure to look
at the length of input strings and password length.

.. the line containing the string 'BASE' may wrap in your newsreader, so watch
for that issue, it needs to on a single line...

Have fun =)

# init_map(password): Initializes and returns the substitution map based on
# the provided password. The password influences the ordering of characters
# in the map.
# # sanitize_password(password): Sanitizes the provided password by removing
# any character not present in the BASE character set. It also ensures that
# each character is unique in the sanitized password.
# # mCrypt(str, password, mode): Depending on the mode, it either encodes or
# decodes the input string str using the substitution cipher. Mode 1 is for
# encoding, and Mode 0 is for decoding. The function returns the transformed
# string.
# # The string variable 'BASE' contains all printable ASCII characters except
# newline ('\n'), which are in the range 32 to 126 inclusive.

BEGIN {

BASE = " !\"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|}~"

e = mCrypt("Obladi Oblada Life Goes On Brah!", "P@ssw0rd", 1)
d = mCrypt(e, "P@ssw0rd", 0)

printf("Encoded: %s\n", e)
printf("Decoded: %s\n", d)

}

# ---------------------------------------------------------------------------

function init_map(password, x, y, p, c, map) {

map = ""
password = sanitize_password(password, BASE)
p = password
x = length(BASE)

while(length(map) < x) {
for(y = 1; y <= length(p); y++) {
c = substr(p, y, 1)
if(index(map, c) == 0) map = map c
}
p = BASE
}

return map

}

# ---------------------------------------------------------------------------

function sanitize_password(password, x, y, c, tmp) {

tmp = ""
y = length(password)

while(++x <= y) {
c = substr(password, x, 1)
if(index(BASE, c) != 0 && index(tmp, c) == 0) tmp = tmp c
}

return tmp
}

# ---------------------------------------------------------------------------

function mCrypt(str, password, mode, x, y, z, c, s, map, buf) {

map = init_map(password)
buf = ""
y = length(str)

while(++x <= y) {
c = substr(str, x, 1)
z = (mode == 1 ? index(BASE, c) : index(map, c))
s = (z == 0 ? c : substr(mode == 1 ? map : BASE, z, 1))
buf = buf s
}

return buf
}

# eof

--
:wq
Mike Sanders