59 lines
1.5 KiB
Python
59 lines
1.5 KiB
Python
'''
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This file reverse engineers and reconstructs the original
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"bcrypt" hash function for the CTF (stored in bcrypt/hash.py).
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This reconstructs implements, namely, precomputation of tables
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of values in the hashing. Allowing bulk computation of hashes
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to be significantly faster.
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'''
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from array import array
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from typing import Optional
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# Constants
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H = 18446744073709551614
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K = 59275109328752
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M = 2**64
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def Rjb(j: int, b: int) -> int:
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return b << j**2
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def Rb(b: int) -> int:
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Rb = 0
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for j in range(8):
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Rb ^= Rjb(j, b)
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return Rb
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'''
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Reconstructed implementation of the "bcrypt" hash function by bpaul.
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NOTE: An optional precomputed R_table is permitted as an arguement.
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'''
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def bcrypt(x: bytes, R_table: Optional[dict[int, int]] = None) -> int:
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h = -2
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for i, b in enumerate(x):
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R = R_table[b] if R_table is not None else Rb(b)
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h = h**2 * (b+1) + ((K * (i+1)) ^ R)
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h %= M
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return h % M
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'''
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Returns a hashmap (python dictionary) of b -> R(b)
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for all b such that: min <= b <= max
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'''
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def calc_R_map(min: int = 0,
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max: int = 255) -> dict[int, int]:
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R_map = {}
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# b from min to max (inclusive)
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for b in range(min, max+1):
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R_map[b] = Rb(b)
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return R_map
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'''
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Same as calc_R_map() but using an array not a hashmap.
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'''
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def calc_R_array(min: int = 0,
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max: int = 255) -> array.array[int]:
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R_array = array('i', [0]*(max-min))
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# b from min to max (inclusive)
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for b in range(min, max+1):
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R_array[b-min] = Rb(b)
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return R_array
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