UNIX for Dummies Questions & Answers

#!/usr/bin/env bash

# @(#) s1	Demonstrate bit-string XOR, perl, with base64 encoding.

pe() { for _i;do printf "%s" "$_i";done; printf "\n"; }
pl() { pe;pe "-----" ;pe "$*"; }
db() { ( printf " db, ";for _i;do printf "%s" "$_i";done;printf "\n" ) >&2 ; }
db() { : ; }
C=$HOME/bin/context && [ -f $C ] && . $C perl base64

PASS=${1-"Password1"}

pl " Results, expecting \"Dz4sLCgwLTtu\" for \"Password1\":"

perl -e 'print '"$PASS"' ^ ( "_" x length('"$PASS"'));' |
base64

exit 0

% ./s1

Environment: LC_ALL = C, LANG = C
(Versions displayed with local utility "version")
OS, ker|rel, machine: Linux, 2.6.26-2-amd64, x86_64
Distribution        : Debian GNU/Linux 5.0.8 (lenny) 
bash GNU bash 3.2.39
perl 5.10.0
base64 (GNU coreutils) 6.10

-----
 Results, expecting "Dz4sLCgwLTtu" for "Password1":
Dz4sLCgwLTtu

% ./s1 snazzy

Environment: LC_ALL = C, LANG = C
(Versions displayed with local utility "version")
OS, ker|rel, machine: Linux, 2.6.26-2-amd64, x86_64
Distribution        : Debian GNU/Linux 5.0.8 (lenny) 
bash GNU bash 3.2.39
perl 5.10.0
base64 (GNU coreutils) 6.10

-----
 Results, expecting "Dz4sLCgwLTtu" for "Password1":
LDE+JSUm

plaintext="abcdefg"

echo "Plaintext: $plaintext"

cyphertext=""
for ((i=0; i < ${#plaintext}; i++ ))
do
   ord=$(printf "%d" "'${plaintext:$i:1}")
   tmp=$(printf \\$(printf '%03o' $((ord ^ 95)) ))
   ciphertext="${ciphertext}${tmp}"
done

echo "Ciphertext: $ciphertext"

plaintext=""
for ((i=0; i < ${#ciphertext}; i++ ))
do
   ord=$(printf "%d" "'${ciphertext:$i:1}")
   tmp=$(printf \\$(printf '%03o' $((ord ^ 95)) ))
   plaintext="${plaintext}${tmp}"
done

echo "Plaintext: $plaintext"

Plaintext: abcdefg
Ciphertext: >=<;:98
Plaintext: abcdefg