AutoKey Cipher in AWK

One more! Meant to post this awhile back. Nifty little cipher
(hopfully post does not suffer from wordwrap)...


# AutoKey Cipher in AWK: Michael Sanders - 2024
#
# https://en.wikipedia.org/wiki/Autokey_cipher
#
# encryption example:
#
# echo "secret message?" | awk -f autokey.awk -v password=hunkyDory68 -v mode=1
#
# decryption example:
#
# echo "ae@beTv?egumIe4" | awk -f autokey.awk -v password=hunkyDory68 -v mode=0

BEGIN {

if (length(password) < 1) exit

if (mode != 1 && mode != 0) exit # 1 encrypt, 0 decrypt

# base character set: beware chars & groupings of chars that require or produce
# escaped values, also throughly randomize/shuffle the string for your own BASE
# if a given char is not included in BASE it will be rendered as is...

BASE = "5KVn?.PB 3iMhqgdxsClJ!7AcLrz@Ra=fTj2w9yIHFkYO8DEmoU0Wp1XZtv#SG4u-*N6Qb%"

}

{ print autokeyCipher($0, password, mode) }

function autokeyCipher(input, key, mode, ak, ic, oc, kc, ix, ox, kx, li, lb, x, buf) {

  li = length(input)
  lb = length(BASE)
  ak = key

  for(x = 1; x <= li; x++) {
    ic = substr(input, x, 1)
    ix = index(BASE, ic)

    if(ix == 0) {
      buf = buf ic
      continue
    }

    kc = substr(ak, (x - 1) % length(ak) + 1, 1)
    kx = index(BASE, kc)

    if(mode == 1) { # encryption mode
      ox = (ix + kx - 1) % lb + 1
      oc = substr(BASE, ox, 1)
      ak = ak ic # append ic to autokey
    } else { # decryption mode
      ox = (ix + lb - kx) % lb
      if(ox == 0) ox = lb
      oc = substr(BASE, ox, 1)
      ak = ak oc # append oc to autokey
    }

    buf = buf oc
  }

  return buf
}

# eof

--
:wq
Mike Sanders