舔到最后应有尽有WP

Problem: [LitCTF 2024]舔到最后应有尽有

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思路

*base64隐写

EXP

  def get_base64_diff_value(s1, s2):
    base64chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/'
    res = 0
    for i in xrange(len(s1)):
        if s1[i] != s2[i]:
            return abs(base64chars.index(s1[i]) - base64chars.index(s2[i]))
    return res

def solve_stego():

    with open('stego.txt', 'rb') as f:
        file_lines = f.readlines()

    bin_str = ''
    for line in file_lines:
        steg_line = line.replace('\n', '')
        norm_line = line.replace('\n', '').decode('base64').encode('base64').replace('\n', '')
        diff = get_base64_diff_value(steg_line, norm_line)

        pads_num = steg_line.count('=')
        if diff:
            bin_str += bin(diff)[2:].zfill(pads_num * 2)

        else:
            bin_str += '0' * pads_num * 2

    res_str = ''

    for i in xrange(0, len(bin_str), 8):

        res_str += chr(int(bin_str[i:i+8], 2))
    print res_str

solve_stego()
​

总结

• 对该题的考点总结