[ACTF新生赛2020]base64隐写

[ACTF新生赛2020]base64隐写

有一个txt文件，看着很想base64加密，直接解密，发现不能直接解出来

根据网上搜索的做法是base64隐写，用脚本直接能跑出来

#encoding:utf-8
def get_base64_diff_value(s1, s2):
    base64chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/'
    res = 0
    for i in xrange(len(s2)):
        if s1[i] != s2[i]:
            return abs(base64chars.index(s1[i]) - base64chars.index(s2[i]))
    return res

def solve_stego():
    with open('/home/kali/桌面/ComeOn!.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)
            print diff
            pads_num = steg_line.count('=')
            if diff:
                bin_str += bin(diff)[2:].zfill(pads_num * 2)
            else:
                bin_str += '0' * pads_num * 2
            print goflag(bin_str)

res_str = ''
def goflag(bin_str):
    res_str = ''
    for i in xrange(0, len(bin_str), 8):
        res_str += chr(int(bin_str[i:i + 8], 2))
    return res_str
print(res_str)

if __name__ == '__main__':
    solve_stego()

要注意的是这个只能用python2运行，而且网上的代码可能会有那个res_str未定义的问题，以及路径，编码问题，注意加上#encoding:utf-8,以及自己的文件所在的路径。并且定义那个res_str变量

标签：bin,隐写,res,base64,2020,str,diff,line
来源： https://www.cnblogs.com/Jinx8823/p/16533510.html