02.base64隐写.py

#coding=UTF-8
#python2下运行，适用于很多base64且解密base64得不到有用的信息的情况

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('./test.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:
            #print bin(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()