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hellman/lacucara.py

Last active June 6, 2024 20:15
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  1. hellman revised this gist Jun 6, 2024. 1 changed file with 5 additions and 0 deletions.
    5 changes: 5 additions & 0 deletions lacucara.py
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    Original file line number Diff line number Diff line change
    @@ -1,7 +1,12 @@
    '''
    Turns out that the output.txt contains images of the 8-byte chunks of the flag under a fixed affine map.
    We can interpolate the map from a bunch of samples and then simply invert the real flag's output.
    '''
    from sage.all import *
    import re
    from binteger import Bin # pip install binteger

    # need to use script log, since the program requires a console
    '''
    script -aq logRANDOM.txt <<EOF
    bash -c 'for i in {1..300}; do head -c 64 /dev/urandom >flag.txt; echo -n "FLAG: 0x"; xxd -ps flag.txt | tr -d "\n"; wine encryptor.exe; done'
  2. hellman revised this gist Jun 2, 2024. No changes.
  3. hellman created this gist Jun 1, 2024.
    50 changes: 50 additions & 0 deletions lacucara.py
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    Original file line number Diff line number Diff line change
    @@ -0,0 +1,50 @@
    from sage.all import *
    import re
    from binteger import Bin # pip install binteger

    '''
    script -aq logRANDOM.txt <<EOF
    bash -c 'for i in {1..300}; do head -c 64 /dev/urandom >flag.txt; echo -n "FLAG: 0x"; xxd -ps flag.txt | tr -d "\n"; wine encryptor.exe; done'
    EOF
    '''
    s = open("logRANDOM.txt").read()
    words = re.findall(r"0x(\w+)\b", s)
    blocks = [[int(w, 16) for w in words[i:i+33]] for i in range(0, len(words), 33)]

    rows = []
    tab = {}
    for block in blocks:
    assert len(block) == 33, len(blocks)
    inp, *block = block
    inp = Bin(inp, 8 * 64).bytes
    assert len(inp) == 64
    a, b, c, d = block[:4]
    # same encryption for all chunks
    # 1 for affine constant
    rows.append(Bin.concat(inp[:8], Bin.concat(a, b, c, d, n=32), 1))

    mat = matrix(GF(2), rows)
    print("rank", mat.rank(), mat.ncols())

    rk = mat.right_kernel().matrix()
    for row in rk:
    print("".join(map(str, row[:64])), end=" ")
    print("".join(map(str, row[64:])))

    assert rk[:64,:64] == 1 # identity matrix
    dec = rk[:, 64:]

    s = open("output.txt").read()
    words = re.findall(r"0x(\w+)\b", s)

    flag = b""
    for i in range(0, len(words), 4):
    print(i, words[i:i+4])
    a, b, c, d = [int(w, 16) for w in words[i:i+4]]
    ct = Bin.concat(Bin.concat(a, b, c, d, n=32), 1).vector
    pt = dec * ct
    print(Bin(pt).bytes)
    flag += Bin(pt).bytes
    print(flag)

    # b'codegate2024{B45IC_i5_n07_d34d_4nd_n3v3r_wi11_b3_2024_MQCJAb4Wr}'