bitwise XOR a string in Bash

Question

I am trying to accomplish a work in Bash scripting. I have a string which i want to XOR with my key.

#!/bin/sh
PATH=/bin:/usr/bin:/sbin:/usr/sbin export PATH

teststring="abcdefghijklmnopqr"

Now how do i XOR the value of teststring and store it in a variable using bash?

Any help will be appreciated.

Basically i am trying to duplicate the result of follwing VB Script:

Function XOREncryption(CodeKey, DataIn)

Dim lonDataPtr
Dim strDataOut
Dim temp
Dim tempstring
Dim intXOrValue1
Dim intXOrValue2


For lonDataPtr = 1 To Len(DataIn) Step 1
    'The first value to be XOr-ed comes from the data to be encrypted
    intXOrValue1 = Asc(Mid(DataIn, lonDataPtr, 1))
    'The second value comes from the code key
    intXOrValue2 = Asc(Mid(CodeKey, ((lonDataPtr Mod Len(CodeKey)) + 1), 1))

    temp = (intXOrValue1 Xor intXOrValue2)
    tempstring = Hex(temp)
    If Len(tempstring) = 1 Then tempstring = "0" & tempstring

    strDataOut = strDataOut + tempstring
Next
XOREncryption = strDataOut
End Function

Answer 1

With the help of these hints i wrote this quickly script to complete Pedro's answer:

#!/bin/bash

function ascii2dec
{
  RES=""
  for i in `echo $1 | sed "s/./& /g"`
  do 
    RES="$RES `printf \"%d\" \"'$i\"`"
  done 
  echo $RES
}

function dec2ascii
{
  RES=""
  for i in $*
  do 
    RES="$RES`printf \\\\$(printf '%03o' $i)`"
  done 
  echo $RES
}

function xor
{
  KEY=$1
  shift
  RES=""
  for i in $*
  do
    RES="$RES $(($i ^$KEY))"
  done

  echo $RES
}


KEY=127
TESTSTRING="abcdefghijklmnopqr"

echo "Original String: $TESTSTRING"
STR_DATA=`ascii2dec "$TESTSTRING"`
echo "Original String Data: $STR_DATA"
XORED_DATA=`xor $KEY $STR_DATA`
echo "XOR-ed Data: $XORED_DATA"
RESTORED_DATA=`xor $KEY $XORED_DATA`
echo "Restored Data: $RESTORED_DATA"
RESTORED_STR=`dec2ascii $RESTORED_DATA`
echo "Restored String: $RESTORED_STR"

Result:

iMac:Desktop fer$ bash test.sh
Original String: abcdefghijklmnopqr
Original String Data: 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 
XOR-ed Data: 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13
Restored Data: 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 
Restored String: abcdefghijklmnopqr