Fourier transformation of binaries

decode.py

#!/usr/bin/python
from scipy.fftpack import rfft, irfft
from scipy import array
import struct
from sys import argv

if len(argv) < 2:
    print "Usage: ./encode.py SOURCEFILE"
    exit()

try:
    filename = argv[1]
    code = open(filename, 'rb').read()
except:
    print "Couldn't open the target file, aborting"
    exit()

# Acquire data discrepancies
misses = struct.unpack('I', code[:4])[0]
fix = code[4:4+5*misses]

# Interpret the binary as an array of floats
code = code[4+5*misses:]
coefs = []
for i in range(0, len(code), 4):
    coefs.append(struct.unpack('f', code[i:i+4]))
coefs=array(coefs)

y2 = irfft(coefs)
code2 = ""
for i in range(len(y2)):
    code2 += struct.pack('f', y2[i])

# Extract fixes
fixmap = {}
for i in range(0, len(fix), 5):
    addr, val = struct.unpack('I', fix[i:i+4])[0], fix[i+4:i+5]
    fixmap[addr] = val

# Build the reverse FFT-transformed binary and apply the fixes
f = open(argv[1].replace(".fft", ""), 'wb')
for i in range(len(code2)):
    if not i in fixmap.keys():
        f.write(code2[i])
    else:
        f.write(fixmap[i])
f.close()

encode.py

#!/usr/bin/python
from scipy.fftpack import rfft, irfft
from scipy import array
import struct
from sys import argv

if len(argv) < 2:
    print "Usage: ./encode.py SOURCEFILE"
    exit()

try:
    filename = argv[1]
    code = open(filename, 'rb').read()
except:
    print "Couldn't open the target file, aborting"
    exit()

# Interpret the binary as an array of floats
y = []
for i in range(0, len(code), 4):
    y.append(struct.unpack('f', code[i:i+4]))
y = array(y)

# FFT/BFFT
coefs = rfft(y)

# Decode for verification
y2 = irfft(coefs)
code2 = ""
for v in range(len(y2)):
    code2 += struct.pack('f', y2[v])

# Check for discrepancies between the original and the encoded-decoded copy
misses, fix = 0, ""
for i in range(len(code)):
    if code[i] != code2[i]:
        misses += 1
        fix += struct.pack("I", i) + code[i]
        print i


# Build the FFT-transformed binary
compressed = struct.pack("I", misses) + fix
for i in range(len(coefs)):
    compressed += struct.pack('f', coefs[i])

f = open(argv[1] + ".fft", 'wb')
f.write(compressed)
f.close()