union-ctf-2021-exah-final.py

# Warning: This is highly unannotated and thus not readable.

A = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789_-'
K = [
    "0000000008258240093",
    "00000032059146620",
    "0000059424680571",
    "00000016501626909",
    "000000010391056299",
    "00000000039819521706",
    "000063129310438"
]

K = list(map(lambda x: int(x), K))

def revert(q):
    u = 0
    for c in q:
        u = 26*u + A.index(c)
    return u

def revert2(q):
    u, _ = q
    return ''.join([A[(u>>(6*i+6)) & 0x3f] for i in range(5)][::-1])


candidates = \
    'bcwtdes dqoagnv hqxmvkq jfntbvq nanqyku pqeytpx pruxdbh sipootq'.split(' ')

results = []

for candidate in candidates:
    k = revert(candidate)
    for i in range(k, 2**36, 26**7):
        results.append(i)

# union
for i in range(5):
    # res = [(u_before_xors, u_after_xors), ...]
    res = sorted([(fu ^ 1763 ^ K[i], fu) for fu in results])
    res = filter(lambda u: ((u[0]>>0)&0x3f) == 0,                   res)
    res = filter(lambda u: ((u[0]>>6)&0x3f) == A.index('union'[i]), res)
    res = list(res)

    print(i, list(map(revert2, res)))
'''
0 ['h4shu']
1 ['C0lln']
2 ['1zioi']
3 ['n_m4o']
4 ['ke5_n']

union{h4shC0ll1zion_m4ke5_????????}
'''

# {
for i in range(5, 6):
    # res = [(u_before_xors, u_after_xors), ...]
    res = sorted([(fu ^ 1763 ^ K[i], fu) for fu in results])
    res = filter(lambda u: ((u[0]>>0)&0x3f) == 0,    res)
    res = filter(lambda u: ((u[0]>>6)&0x3f) == 0x3f, res)
    # In hexa, A.indexOf('{') == -1.
    # This may cause rounding issue and the fourth character should be increased by one.
    res = list(res)

    print(i, list(map(revert2, res)))
'''
5 ['HAXD-']
       ^--- This should be an E as line 63 suggests
        
union{h4shC0ll1zion_m4ke5_HAXE????}
'''

# h
for i in range(6, 7):
    # res = [(u_before_xors, u_after_xors), ...]
    res = sorted([(fu ^ 1763 ^ K[i], fu) for fu in results])
    res = filter(lambda u: ((u[0]>>0)&0x3f) == 0,            res)
    res = filter(lambda u: ((u[0]>>6)&0x3f) == A.index('h'), res)
    res = list(res)

    print(i, list(map(revert2, res)))
'''
6 ['_sadh']

union{h4shC0ll1zion_m4ke5_HAXE_sad}
'''