findbytes.py

TARGET = b"\xDE\xAD\xBE\xEF"

import random

def generateTestFile():
    with open("test.bin", "wb") as f:
        randData = bytes(random.getrandbits(8) for _ in range(1024))
        f.write(randData)
        # Grab a random number and place the bytes 0xDEADBEEF in that location
        randOffset = random.randint(0, 1024)
        f.seek(randOffset)
        f.write(b"\xDE\xAD\xBE\xEF")
        print(f"Wrote 0xDEADBEEF at offset: {hex(randOffset)}")

def find():
    foundBytes = 0
    offset = 0

    with open("test.bin", "rb") as f:
        chunk = f.read(512)
        while chunk:
            for byte in chunk:
                offset += 1
                if byte == TARGET[foundBytes]:
                    # print(f"Found byte: {hex(byte)} matching {TARGET[foundBytes]} at offset: {hex(offset)}")
                    foundBytes += 1
                else:
                    # Avoid ignoring a byte if it's the first byte of the target
                    if byte == TARGET[0]:
                        foundBytes = 1
                        continue
                    # if foundBytes > 0:
                    #     print(f"Byte: {hex(byte)} does not match target byte: {hex(TARGET[foundBytes])}, resetting")
                    foundBytes = 0
                if foundBytes == len(TARGET):
                    print(f"Found the 4 bytes at offset: {hex(offset-4)}")
                    return True

            chunk = f.read(512)
        # print(f"Reached end of file at offset: {hex(offset)}")
        return False

# Run find until it fails
generateTestFile()
while find():
    generateTestFile()

print("Failed to find the bytes")