1. Capture The Fun: Cyber Sea Game 2017

    Wed 29 November 2017 · 5 min read

    This post is part 2 of the "Capture The Fun" series:

    1. Capture The Fun: Cyber Jawara 2017
    2. Capture The Fun: Cyber Sea Game 2017
    3. Capture The Fun: SECCON 2017 Final International Competition

    After Cyber Jawara

    Me and my team are fortunate enough to be selected to represent Indonesia in Cyber Sea Game 2017 as part of the 1st place prize. It's a CTF event held by partnership between Japan and ASEAN countries (I think, I'm not sure). The winner of the event …

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  2. Cyber Sea Game 2017: addcrypto (50)

    Wed 29 November 2017 · < 1 min read

    We are given a file, encrypt.py, which looks as follows.

    import os
from flag import flag

message = os.urandom(8) + flag

cipher = ''
for i in range(0, len(message) - 1):
    cipher += chr((ord(message[i]) + ord(message[i+1]) + ord(message[i+1])) & 0xff)

print cipher.encode('hex')
# 4c8f7236c7b259b4e9b792929f2d59534437394530392a2547645958522d3d3b4e3e412c2f2a47314b604d483849342534413e516673 …
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  3. Cyber Sea Game 2017: rsa-8192 (200)

    Wed 29 November 2017 · < 1 min read

    We are given a file, encrypted.txt, which looks as follows.

    encrypted = flag^e mod N

N=929412161736416785602626791790087761924898902195151595398647919800777946023488971853180598176692598583294061182260536041579346366926172653588840221567273437362595402878942949261351013183228816076787208298761416393920642857987212821185440640229264390419503134199675174977584782229111062529809687171117150001744486594819183472678424697917104835410391461624730889726473874533632011783818612095039231758588125644714046393001791112810853913402405581873909038522129835207451007166051445611924869493431837474285007276641743601868212445343248507996492168302629410158793171095836266438216336450410161777445930018295413880788397817212920901086111768107584700273194248624078825784962833148389339669672770486880797307481695588172832838731072379885756990402094668632885608688308703281839275920814948615941253077843879626529478150269189961487485485588639730236538541375331823636862137530268960752698621771461443704327244021041422495986281380147586211470392418121029373841474934960486004859939618776068437679091746000882065500417603392927878932556252121339876316869065207294672799230304843433288112308586240048684735313520164083326788976779830776801482533953926103609143333554819874985879730182046630820535196380040115825136940584589556785820159343472924511678054586101279599213597041601780382296431834866858061507446104315668473990065085836000677940559666983863740858655209448321924892616633958276590031999377342119486934203280802950550853609192641981061152748812514091191340011124311081998324364749868579702401217654561296975509502208974088057282185982036347055436781944503659441121489871215835821003778237875885585700465817962525400543288824177317817062453958271388228532199292458847881512536878190894921450789438099744648090308652667907702590059579778875658483803814963849425246348271265297992326326941649385344794434378497144236903691683724320406798550633839076630007346411875416248546336032185298058900521975982336237334536607755792300625619630545602773119916582573302060747209289533363253570250473519076096695447047922887567718357635771477087257951066557774977631702031440524698209045937363875790679216746249380353174688379191327766840638039388162445662493445777856792810700198251083685207125399710828301628160312264601730356710220261724123846339093165967118971272821247106002282782902865842552867964918068336459439425481643750939492002728297110520672697512136349144736715821664013325546531282992945883469394942896186838909299361507395054625609900948608639067118377943217351
e=65537
encrypted=920588809098419925304898815996779959024923992725236480766957762101020068092418642972569896909288446822625160018245995852395637010359546968987469161375560974732331888587499575726726591661288086170102991231536351472553667136912003817645761994113867006023358064959804334508836786614546373318854185561928539181380849135202589436399469446278977853873976388512625983066695071220448389094452382204859072246204132607199499483725325567718766144169704838594296010882715656390868083309425868664311629487870655537301587586264593373623106904074718645449224372238734853263892364592224060906009118410260996474851170094609808378917112241913945371712277407646776651895736210620267993703347840913541477388590431559378925211730392071715903857032396752409447351784452479847357247902830713107054131920974381233928620873147787352397722780557371121588138822734422526916591197108637109219278170352817301806094020568558870258047526598307845757398567950006581582539714075107753798978096510308355532420719999999220855138247162168113460577910905929588333387729891130789423649360964154825883032891254447994769161274294764104742371937868945566163338795266034258979330588673875819190729858101607459440752551327488554472157318363257082223209451608433992248074386159317605908434880514654833712622074369971266584704933749205856068601008066620986626613108276972360189307015131946572931252688986331609366041663453234811061216223134001974803179901785278084643248758399580372104073097458529704426905971473072151381373448553361414418342456280135383419519503028786544292302907897461141075166092520323444990854104372309393440260002551733596011221728567186544196673107818614484776574487330137101004134890658956591489639306529923386792687879390716232617992555567785121188340568023697639047632424964759610425447619800320974777755083401005364154241941027256239760103909197224362499684459388821532418774937557650857921765385859799914470867641296667037230734819015690775890840326939101061216700887599083952915657512483532308094437422732323767769158944259841802993244806549824743056280460644331001819024060314281381987785996895717885719094296415336981352928519848848055894963780262847910621421107636554884980968204334872719316159028387134320156378724268116858255133532724522370999208549105477046537264757515852756867521989580046767357180880003025052171778061564683996167899012373574038101166777008676727628024284803295629377550189159115681868387149280045459828574367106610925183390170585407262031209717446921115630

    Since there's no gimmick in the encryption process, let's try factorize N. Factoring N with Fermat's factorization included in Yafu yield p and q used to create N …

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