#!/bin/bash
# Show the impact of errors in ciphertext on the different modes of operation

# List of ciphers/modes to use (using format of OpenSSL)
modes="des-ecb des-cbc des-cfb des-ofb"

# Base of plaintext file
plaintext="repeated"

# Key
key="0000000000000013"

# IV
iv="0000000000000000"

# For each cipher/mode ...
for m in ${modes}
do
	echo "Mode: $m"

	# Encrypt the plaintext
	openssl enc -${m} -e -in ${plaintext}.txt -out ${plaintext}-$m.enc -iv ${iv} -K ${key}
	
	echo "Original ciphertext:"
	xxd  ${plaintext}-$m.enc

	# Find the first word of ciphertext
	firstword=`xxd ${plaintext}-$m.enc | head -1 | cut -d " " -f 2 | cut -c 1`
	# Find the second word of ciphertext
	secondword=`xxd ${plaintext}-$m.enc | head -1 | cut -d " " -f 2 | cut -c 2`

	# We are going to change the second word, incrementing by 1
		if [ "${secondword}" = "0" ]
		then	
			newbyte="1";
		elif [ "${secondword}" = "1" ]
		then
			newbyte="2";
		elif [ "${secondword}" = "2" ]
		then
			newbyte="3";
		elif [ "${secondword}" = "3" ]
		then
			newbyte="4";
		elif [ "${secondword}" = "4" ]
		then
			newbyte="5";
		elif [ "${secondword}" = "5" ]
		then
			newbyte="6";
		elif [ "${secondword}" = "6" ]
		then
			newbyte="7";
		elif [ "${secondword}" = "7" ]
		then
			newbyte="8";
		elif [ "${secondword}" = "8" ]
		then
			newbyte="9";
		elif [ "${secondword}" = "9" ]
		then
			newbyte="a";
		elif [ "${secondword}" = "a" ]
		then
			newbyte="b";
		elif [ "${secondword}" = "b" ]
		then
			newbyte="c";
		elif [ "${secondword}" = "c" ]
		then
			newbyte="d";
		elif [ "${secondword}" = "d" ]
		then
			newbyte="e";
		elif [ "${secondword}" = "e" ]
		then
			newbyte="f";
		else
			newbyte="0";
		fi

	# Replace the first byte with the modified byte
	sed 's/\x'${firstword}${secondword}'/\x'${firstword}${newbyte}'/' ${plaintext}-$m.enc > ${plaintext}-$m-mod.enc

	echo "Modified ciphertext"
	xxd ${plaintext}-$m-mod.enc

	# Decrypt the original ciphertext
	openssl enc -${m} -d -in ${plaintext}-$m.enc -out decrypt-$m.txt -iv ${iv} -K ${key}

	# Decrypt the modified ciphertext
	openssl enc -${m} -d -in ${plaintext}-$m-mod.enc -out decrypt-$m-mod.txt -iv ${iv} -K ${key}

	echo "Original decrypted plaintext"
	xxd decrypt-$m.txt
	echo "Modified decrypted plaintext"
	xxd decrypt-$m-mod.txt

	echo " "

done