base64隐写

迈不过友情╰ 2022-05-28 11:39 304阅读 0赞

# 详情看这个 #

[https://tr0y.wang/2017/06/14/Base64steg/][https_tr0y.wang_2017_06_14_Base64steg]

# 题目参考这个 #

bWFpbigpe2ludCBpLG5bXT17KCgoMSA8PDEpPDwgKDE8PDEpPDwoMTw8Cm==  
ICAgICAgIDEpPDwoMTw8KDE+PjEpKSkrKCgxPDwxKTw8KDE8PDEpKSksKCgoMQp=  
ICAgICAgIDw8ICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAxKQq=  
ICAgICAgIDw8ICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAoMQp=  
ICAgICAgIDw8MSk8PCgxPDwxKTw8ICAgICAgICAgKDE8PDEpKS0oKDE8PDEpPDwoCr==  
ICAgIAkxPDwxKTw8KDE8PDEpKSsgICAgICAgICgoMTw8MSk8PCgxPDwoMT4+Ch==  
ICAgICAgIDEpKSkrKDE8PCgxPj4xKSkpICAgICAgICAgICAgICAgICAgICAgICAgLAq=  
ICAgICAgICgoKDE8PDEpPDwoMTw8MSkgICAgICAgICAgICAgICAgICAgICAgICA8PAo=  
ICAgICAgICgxPDwxKTw8KDE8PDEpKS0oKDEgPDwxKTw8KDE8PDEpIDw8KDE8PCgxCl==  
ICAgICAgID4+MSkpKS0oKDE8PDEpPDwoMTw8KDE+PjEpKSkpLCgoKDE8PDEpCp==  
ICAgICAgIDw8KCAgICAxPDwgICAgICAgICAgICAgICAgICAgICAgICAgIDEpCt==  
ICAgICAgIDw8KCAgICAxPDwgICAgICAgICAgICAgICAgICAgICAgICAgIDEpCu==  
ICAgICAgIDw8KCAxPDwxKSktKCgxIDw8MSk8PCAoMSA8PDEpPDwoMSA8PAr=  
ICAgICAgICgxPj4xKSkpLSgoMTw8MSk8PCgxPDwoMT4+MSkpKSksKCgoMTw8MSk8PAo=  
ICAgICAgICgxPDwxKTw8KDE8PDEpPDwoMTw8MSkpLSgoMTw8MSk8PCgxPDwxKTw8KAr=  
ICAgICAgIDE8PCgxPj4xKSkpLSgxPDwoMT4+ICAgICAgICAgIDEpKSksKCgoMTw8MSk8PAq=  
ICAgICAgICgxPDwxKTw8KDE8PDEpKSsgICAgKCgxPDwxKSAgICA8PCgxPDwxKTw8Ch==  
ICAgICAgICgxPDwoMT4+MSkpKS0oKCAgICAgMTw8MSk8PCggICAgICAxPDwoMT4+Co==  
ICAgICAgIDEpKSkpLCgoMTw8MSk8PCAgICAgICgxPDwxKSAgICAgICAgPDwoMTw8MSkpCl==  
ICAgICAgICwoKCgxPDwxKTw8KDE8PCAgICAgIDEpPDwoICAgICAgIDE8PDEpPDwoMTw8MSkpLQr=  
ICAgICAgICgoMTw8MSk8PCgxPDwxKSAgICAgKS0oMTw8KDE+PjEpICAgICAgKSksKCgoCj==  
ICAgICAgIDE8PDEpPDwoMTw8MSk8PCggICAgMTw8MSk8PCgxPDwxKSktICAgICgoMQp=  
ICAgICAgIDw8ICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgMQq=  
ICAgICAgICkgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICA8PAp=  
ICAgICAgICgxPDwxKTw8KDE8PCgxPj4xKSkpLSgxPDwoMT4+MSkpKSwgKCgoMTw8MQp=  
ICAgICAgICk8PCgxPDwxKTw8KDE8PDEpPDwoMTw8MSkpLSgoMTw8MSk8PCAoMSAgCk==  
ICAgICAgIDw8ICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAxCp==  
ICAgICAgICkgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgIDw8Cn==  
ICAgICAgICggICAgIDE8PCgxPj4xKSkpKyAgICAoMTw8MSkpLCgoKDEgICAgIDw8Cj==  
ICAgICAgIDEpICAgIDw8KDE8PDEpPDwgICAgICAoMTw8MSk8PCgxICAgICAgIDw8Ck==  
ICAgICAgIDEgICAgICkpLSgoMTw8MSk8PCAgICAoMTw8MSk8PCgxICAgICAgIDw8Cj==  
ICAgICAgICggICAgIDE+PjEpKSktKCgxICAgICAgPDwxKTw8KDE8PCAgICAgICAoCj==  
ICAgICAgIDEgICAgID4+MSkpKSksKCgoMSAgICAgPDwxKTw8KDEgICAgICAgIDw8Cg==  
ICAgICAgIDEgICAgICk8PCgxPDwxKTw8KCAgICAgMTw8MSkpLSgoMSAgICAgIDw8Cm==  
ICAgICAgIDEgICAgICk8PCgxPDwxKTw8ICAgICAoMTw8MSkpKygoICAgICAgICAxCv==  
ICAgICAgIDw8MSk8PCgxPDwoMT4+MSkpKSksKCgoMTw8MSk8PCgxPDwxKSA8PCgxCm==  
ICAgICAgIDw8MSkpKygxPDwoMT4+MSkpKSwoKCgxPDwxKTw8KDE8PDEpKSArKCgxCs==  
ICAgICAgIDw8MSk8PCAoMTw8KDE+PjEpKSkgKyAoMTw8ICgxPj4xKSkpfSA7Zm9yCn==  
ICAgICAgIChpPSgxPj4xKTtpPCgoKDE8PDEpPDwoMSA8PDEpKSsoKDEgPDwxKTw8KAr=  
ICAgICAgIDE8PCgxPj4xKSkpKygxPDwxKSk7aSsrKSAgcHJpbnRmKCIlYyIsbltpXSk7fQp=

解出来是:flag\{8aseIsC0ol\}

# 加密脚本 #

# -*- coding: cp936 -*-
    import base64
    
    flag = 'Tr0y{Base64isF4n}'  # flag
    bin_str = ''.join([bin(ord(c)).replace('0b', '').zfill(8) for c in flag])
    
    base64chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/'
    
    with open('0.txt', 'rb') as f0, open('1.txt', 'wb') as f1:  # '0.txt'是明文, '1.txt'用于存放隐写后的base64
        for line in f0.readlines():
            rowstr = base64.b64encode(line.replace('\n', ''))
            equalnum = rowstr.count('=')
    
            if equalnum and len(bin_str):
                offset = int('0b' + bin_str[:equalnum * 2], 2)
                char = rowstr[len(rowstr) - equalnum - 1]
                rowstr = rowstr.replace(char, base64chars[base64chars.index(char) + offset])
                bin_str = bin_str[equalnum * 2:]
    
            f1.write(rowstr + '\n')

# 解密脚本 #

# -*- coding: cp936 -*-
    b64chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/'
    #https://tr0y.wang/2017/06/14/Base64steg/
    with open('1.txt', 'rb') as f:
        bin_str = ''
        for line in f.readlines():
            stegb64 = ''.join(line.split())
            rowb64 = ''.join(stegb64.decode('base64').encode('base64').split())
    
            offset = abs(b64chars.index(stegb64.replace('=', '')[-1]) - b64chars.index(rowb64.replace('=', '')[-1]))
            equalnum = stegb64.count('=')  # no equalnum no offset
    
            if equalnum:
                bin_str += bin(offset)[2:].zfill(equalnum * 2)
    
            print ''.join([chr(int(bin_str[i:i + 8], 2)) for i in xrange(0, len(bin_str), 8)])  # 8位一组

[https_tr0y.wang_2017_06_14_Base64steg]: https://tr0y.wang/2017/06/14/Base64steg/