Convert hex string to usably hex

Question

I want to convert a hex string I read from a file "0xbffffe43" to a value written in little endian "\x43\xfe\xff\xbf".

I've tried using struct.pack but it requires a valid integer. Everytime I try to cast hex functions it will convert the 43. I need this for an assignment around memory exploits.

I have access to python 2.7

a = "0xbffffe43"
...
out = "\x43\xfe\xff\xbf"

Is what I want to achieve

score 1 · Answer 1 · answered Nov 23 '19 at 16:09

1

You can try doing:

my_hex = 0xbffffe43
my_little_endian = my_hex.to_bytes(4, 'little')
print(my_little_endian)

answered Nov 23 '19 at 16:09

Magofoco

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this doesn't work with python 2. Covered in the duplicate (for python 3) – Jean-François Fabre Nov 23 '19 at 16:11
Thanks, I did not know – Magofoco Nov 23 '19 at 16:11
1

besides OP has probably input defined as string. – Jean-François Fabre Nov 23 '19 at 16:12

score 1 · Accepted Answer · answered Nov 23 '19 at 16:15

You have a string in input. You can convert it to an integer using int and a base.

>>> a = "0xbffffe43"
>>> import struct
>>> out = struct.pack("<I",int(a,16))
>>> out
b'C\xfe\xff\xbf'

The b prefix is there because solution was tested with python 3. But it works as python 2 as well.

C is printed like this because python interprets printable characters. But

>>> b'C\xfe\xff\xbf' == b'\x43\xfe\xff\xbf'
True

see:

Convert hex string to usably hex

2 Answers2