'''
This file reverse engineers and reconstructs the original 
"bcrypt" hash function for the CTF (stored in bcrypt/hash.py).
This reconstructs implements, namely, precomputation of tables
of values in the hashing. Allowing bulk computation of hashes
to be significantly faster.
'''

from array import array
from typing import Optional

# Constants
H = 18446744073709551614
K = 59275109328752
M = 2**64

def Rjb(j: int, b: int) -> int:
    return b << j**2

def Rb(b: int) -> int:
    Rb = 0
    for j in range(8):
        Rb ^= Rjb(j, b) 
    return Rb

'''
Reconstructed implementation of the "bcrypt" hash function by bpaul.
NOTE: An optional precomputed R_table is permitted as an arguement.
'''
def bcrypt(x: bytes, R_table: Optional[dict[int, int]] = None) -> int:
    h = -2
    for i, b in enumerate(x):
        R = R_table[b] if R_table is not None else Rb(b)
        h = h**2 * (b+1) + ((K * (i+1)) ^ R)
        h %= M
    return h % M

'''
Returns a hashmap (python dictionary) of b -> R(b)
for all b such that: min <= b <= max
'''
def calc_R_map(min: int = 0,
               max: int = 255) -> dict[int, int]:
    R_map = {}
    # b from min to max (inclusive)
    for b in range(min, max+1):
        R_map[b] = Rb(b)
    return R_map

'''
Same as calc_R_map() but using an array not a hashmap.
'''
def calc_R_array(min: int = 0,
                 max: int = 255) -> array.array[int]:
    R_array = array('i', [0]*(max-min))
    # b from min to max (inclusive)
    for b in range(min, max+1):
        R_array[b-min] = Rb(b)
    return R_array