本题压缩包解压后得到一个txt文件。里面全是base64密码。
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SSwgZXNwaW9uYWdlIGFnZW50cyB1c2VkIHBob3RvZ3JhcGhpY2FsbHkgcO==cm9kdWNlZCBtaWNyb2RvdHMgdG8gc2VuZCBpbmZvcm1hdGlvbiBiYWNrIGFuZH==IGZvcnRoLiBNaWNyb2RvdHMgd2VyZSB0eXBpY2FsbHkgbWludXRlLCBhcHByb3hpbWF0ZWx5IGxlc3MgdGhhbiB0aGUgc2l6ZSBvZiB0aGUgcGVyaW9kIHByb2R=dWNlZCBieSBhIHR5cGV3cml0ZXIuIFdXSUkgbWljcm9kb3RzIG5lZWRlZCB0byBiZSBlbWJlZGRlZB==IGluIHRoZSBwYXBlciBhbmQgY292ZXJlZCB3aXRoIGFuIGFkaGVzaXZlIChzdWNoIGFzIGNvbGxvZGlvbikuIFR=aGlzIHdhcyByZWZsZWN0aXZlIGFuZCB0aHVzIGRldGVjdGFibGUgYnkgdmlld2luZyBhZ2FpbnN0IGdsYW5jaW5nIGxpZ2h0LiBBbHRlcm5hdGl2ZSB0ZWNobmlxdWVzIGluY2x1ZGVkIGluc2VydGluZyBtaWNyb2RvdHMgaW50byBzbGl0cyBjdXQgaW50byB0aGUgZWRnZSBvZv==IHBvc3QgY2FyZHMuDQoqIER1cmluZyBXb3JsZCBXYXIgSUksIGEgc3B5IGZvciB=SmFwYW4gaW4gTmV3IFlvcmsgQ2l0eSwgVmVsdmFsZWW=IERpY2tpbnNvbiwgc2VudCBpbmZvcm1hdGlvbiB0byBhY2NvbW1vZGF0aW9=biBhZGRyZXNzZXMgaW4gbmV1dHJhbCBTb3V0aCBBbWVyaWO=YS4gU2hlIHdhcyBhIGRlYWxlciBpbiBkb2xscywgYW5kIG==aGVyIGxldHRlcnMgZGlzY3Vzc2VkIGhvdyBtYW55IG9mIHRoaXMgb3IgdGhhdCBkb2xsIHRvIHNoaXAuIFRoZSBzdGVnb3RleHQgd2FzIHRoZSBkb2xsIG9yZGVycywgd2hpbGUgdGhlIGNvbmNlYWxlZCAicGxhaW50ZXh0IiB3YXMgaXRzZWxmIGVuY2+=ZGVkIGFuZCBnYXZlIGluZm9ybWF0aW9uIGFib3V0IHNoaXAgbW92ZW1lbnRzLF==IGV0Yy4gSGVyIGNhc2UgYmVjYW1lIHNvbWV3aGF0IGZhbW91cyBhbmQgc2hlIGJlY2FtZSBrbm93biBhcyB0aGX=IERvbGwgV29tYW4uDQoqIENvbGQgV2FyIGNvdW50ZXItcHJvcGFnYW5kYS4gSW4gMTk2OCwgY3JldyBtZW1iZW==cnMgb2YgdGhlIFVTUyBQdWVibG8gKEFHRVItMikgaW50ZWxsaWdlbmNlIHNoaXAgaGVsZCBhcyBwcm==aXNvbmVycyBieSBOb3J0aCBLb3JlYSwgY29tbXVuaWNhdGVkIGluIHNpZ25=IGxhbmd1YWdlIGR1cmluZyBzdGFnZWQgcGhvdG8gb3Bwb3J0dW5pdGllcywgaW5mb3JtaW5nIHRoZSBVbml0ZWQgU3RhdGVzIHRoZXkgd2VyZSBub3QgZGVmZWN0b3JzIGJ1dCByYXRoZXIgd2VyZSBiZWluZyBoZWxkIGNhcHRpdmUgYnkgdGhlIE5vcnRoIEtvcmVhbnMuIEluIG90aGVyIHBob3RvcyBwcmVzZW50ZWQgdG8gdGhlIFVTLCBjcmV3IG1lbWJlcnMgZ2F2ZSAidGhlIGZpbmdlciIgdG8gdGhlIHVuc3VzcGVjdGluZyBOb3J0aCBLb3JlYW5zLCBpbiBhbiBhdHRlbXB0IHRvIE==ZGlzY3JlZGl0IHBob3RvcyB0aGF0IHNob3dlZCB0aGVtIHNtaQ==bGluZyBhbmQgY29tZm9ydGFibGUuDQoNCi0tDQpodHRwOi8vZW4ud2lraXBlZGlhLm9yZw==L3dpa2kvU3RlZ2Fub2dyYXBoeQ0K
base64隐写效率很低，每个语句最多只有2*2个隐写位。
所以使用大佬的Python2代码
def get_base64_diff_value(s1, s2):base64chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/'res = 0for i in xrange(len(s1)):if s1[i] != s2[i]:return abs(base64chars.index(s1[i]) - base64chars.index(s2[i]))return resdef solve_stego():with open('/Users/dapao/Desktop/XCTF/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 * 2res_str = ''for i in xrange(0, len(bin_str), 8):res_str += chr(int(bin_str[i:i+8], 2))print res_strsolve_stego()
运行后得到：
Base_sixty_four_point_five
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