Python - counting up in hex

Question

What is a good way to count up in hex and append the result to the end of a larger hex string? I am trying to format a string to be used in a padding oracle attack. The strings will be concatenated together to form an HTTP request.

I have a two 32 character hex strings. 'g' is a guess, pad is the padding oracle. Basically what I need to do is have the last byte of g count up in hex from 0x00 to 0xff.The code I have so far is:

split = [value[x:x+32] for x in range (0, len(value), 32)] #Split the CT into 16 byte chunks IV = unhexlify(split[0]) c0 = unhexlify(split[1]) c1 = unhexlify(split[2]) c2 = unhexlify(split[3]) g = unhexlify("00000000000000000000000000000000") pad = unhexlify("00000000000000000000000000000001") pad_xor_guess = xorb(g, pad) c1_prime = xorb(pad_xor_guess, c1) attack = str(hexlify(c1_prime + c2).decode())

'attack' will be passed into the query method that will append the attack string to the web address. Now the part I am stuck on is that I have to basically send up to 256 HTTP requests to guess one byte of the plaintext. How can I use a for loop to "count up" from 00 to ff, appending the result to g in such a way that it can be xor'd with the pad and the chosen ciphertext block? SO far I have been going down this path, but I am stuck on how to make this work with the hex strings.

for i in range(0, 20): #g = bytes([i]) print(bytes([i]),end=' ') #print(g, end=' ')

for i in range(255): hex(i)

user2097159
– user2097159

2015-02-10 13:29:11 +00:00
Commented Feb 10, 2015 at 13:29 — user2097159
– user2097159, Commented Feb 10, 2015 at 13:29

Tim Hopper · Accepted Answer · 2020-03-10 22:49:52Z

For given int value, hex function will give you the hex string preceded with 0x, so hex(i)[2:] gives you the hex number itself, zfill will make sure you get two digits for the single digits numbers

for i in range(256): print(hex(i)[2:].zfill(2))

You might also want to consider making it all caps, since some parsers rely on hex being written in capital letters, so the example will be:

for i in range(256): print(hex(i)[2:].zfill(2).upper())

And if you just need the full string, you don't need to append them one by one, you can create the string in one go:

hex_str = "".join([hex(i)[2:].zfill(2).upper() for i in range(256)])

jonrsharpe · Accepted Answer · 2015-02-10 13:42:37Z

I guess you mean something like:

>>> for i in range(256): print "{:02x}".format(i) # or X for uppercase 00 01 02 ... fd fe ff

Collectives™ on Stack Overflow

Python - counting up in hex

2 Answers 2

Comments

Comments

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Related