Steganography

decToChar () {

# converts single-byte decimal value to equivalent character

# arg: decimal number from 0-255

# out: one character

echo -n -e "\x$(printf %02X "$1")"

}

readDecimal() {

# Read the n'th decimal from a file. This function looks at the 2 least significant bits of 4 consecutive bytes in

# the given file and pastes them together to decode the decimal.

# arg1: decimal offset

# arg2: filename from which the given decimal should be read and decoded.

readcharDec () {

# read one character from file & convert to equivalent decimal value

# arg1: offset (# of bytes to skip before reading)

# arg2: filename

# out: decimal value from 0-255

VAL=$(xxd -p -l1 -s $1 $2)

printf %d "0x$VAL"

}

readLSB2 () {

# read the 2 LSB's from the byte at the given position in the given file.

# arg1: byte offset

# arg2: filename

READ_BYTE=$(readcharDec $1 $2)

echo $(( READ_BYTE & 3 ))

}

CURRENT_DECIMAL=0

IDX=$1

FILE=$2

for ((j = 3; j > 0; j--)); do

CURRENT_VAL=$(readLSB2 $(( IDX * 4 + j )) $FILE)