#!/usr/bin/env python

import re, os
from sys import byteorder
from hashlib import sha256

# match this many hexadigits
# must be corroborated within the script
depth = 6
# bytes per message
message_size = 1

internal_sram_hash = input("Internal SRAM Hash: ").lower()

target = re.sub(r'\s+', '', input("Encoded Target: ")).lower()

# calculate LUT for given parameters
all_hashes = {}
for i in range (0, 1<<(8*message_size)):
    key = sha256(i.to_bytes(length=message_size, byteorder='big', signed=False)).hexdigest()[:depth]
    all_hashes[key] = i
dedup = list(dict.fromkeys(all_hashes.keys()))
print(f"distinct values in all_hashes: {len(dedup)}\n")

sram: bytearray = bytearray()

# decode
print("Decoded:")
for loc in range (0, len(target), depth*message_size):
    key = target[loc:loc+depth]
    try:
        value = all_hashes[key]
        if value:
            print(f"{value:x}", end="")

    except KeyError:
        value = 0x00
    sram.append(value)

# write to file
with open("carfax.bin", 'wb') as output:
    output.write(sram)

print("")
# hexdump file
os.system("xxd carfax.bin")

# check hash against provided value
while len(sram) < 0x1000:
    sram.append (0)
print (f"{sha256(sram).hexdigest()}\n{internal_sram_hash}")

if (sha256(sram).hexdigest().lower() == internal_sram_hash.lower()):
    print("Hash match!")