#!/bin/bash
# Count the number of bits that in ciphertext when changing one bit
# of input key

# STEP 1. INITIALISE VARIABLES
# ============================

# The plaintext to encrypt
plaintext="stevengo"

# Keys. The original key, and then set of modified keys, differing
# from the original key by 1 bit.
key="0000000000000001"
modkeys="0000000000000002 0000000000000004 0000000000000008 0000000000000010 0000000000000020"

# IV
iv="0000000000000000"

# Base of the filename. filebase.txt is plaintext, filebase.enc is 
# ciphertext.
filebase="name"

# STEP 2. ENCRYPT THE PLAINTEXT
# =============================

# Create the plaintext file. The -n option for echo means a newline
# will NOT be added to the end, so the file is exactly 8 bytes (since
# the input string is 8 characters). That is, 64 bits or 1 block.
echo -n ${plaintext} > ${filebase}.txt

# Encrypt the plaintext to get the original ciphertext
openssl enc -des-ecb -e -in ${filebase}.txt -out ${filebase}.enc -iv ${iv} -K ${key} -nopad


# STEP 3. CONVERT CIPHERTEXT TO BINARY STRING
# ===========================================

# Later we will compare the binary ciphertext with the original key 
# against the binary ciphertexts for the modified keys. To do so,
# we will save the binary value as a set of 0's and 1's in a text file
# then compare the text files. 

# xxd is used to get the binary form of the ciphertext, then cut
# is used to select the binary value from the output of xxd. The
# result, a string of 64 0's or 1's, is saved in a .bin file.
xxd -b -c 8 -g 8 ${filebase}.enc | head -1 | cut -d " " -f 2 > ${filebase}.bin

# Display the binary ciphertext
cat ${filebase}.bin

echo " "

# STEP 4. ENCRYPT USING MODIFIED KEYS
# ===================================

# For each key in the list of modified keys
for k in $modkeys
do
	# Encrypt using the modified key
	openssl enc -des-ecb -e -in ${filebase}.txt -out ${filebase}-${k}.enc -iv ${iv} -K ${k} -nopad

	# Convert the ciphertext to a binary string in a file
	xxd -b -c 8 -g 8 ${filebase}-${k}.enc | head -1 | cut -d " " -f 2 > ${filebase}-${k}.bin

	# Display the binary ciphertext
	cat ${filebase}-${k}.bin

	# About the count the bits different ...
	echo -n "Bits different from original ciphertext: "

	# Compare the binary string with the original, counting the
	# number of values that differ
	cmp -l ${filebase}.bin ${filebase}-${k}.bin | wc -l

	echo " "
done