[CRYPTO] DeFUNct Ransomware - 50 pts
Challenge Description:
We are given with the following files:
memos.enc content:
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
public content:
n: 795569463642685540507503580717531982215679866156448758181874864294322245115046429295501396806569726084791213843313411985306755767933614251017259685360119715465741448841742926933764058184678978561438979554324014291467144646477238464467422645352253054043072408503415623126059018449111807300294890437634529289983603557882115343971407081044050231310858245171002149317227947666679143716043142141154344524386085333349328691743473103727587822968025700198172293605188589348169121979328380110985341428872278372426313622759225108517531628814853640680656657769539723198346005032762702856464738405070059566116940640592020837592563966093405895649052241416909627641069000138027201809936286028443581259045590752809132011594533609186039058798304319124598876514669458750171121861029071117458575853963148168447032328126766812085206373608016609150982512467597800331177524543178311636877811255184421602626713179220562081413985985692847372669113031244726086691179028200044542399429299315486513734144695492816493025225952668485937918985944213972980220480476191347009337324778384697829597183756976186825413917475597248616769321954150777672675555280228376126308362907381766363071890237458517881243184612898247096962136202978853341989193954815333784856612689
e: 13337
Since we have the value of n, maybe it can be factored even though it’s very large. Let’s go to this large number factorization website.
We actually have an answer but we’re only concerned with Euler’s totient:
euler_tot = 795569463642685540507503580717531982215679866156448758181874864294322245115046429295501396806569726084791213843313411985306755767933614251017259685360119715465741448841742926933764058184678978561438979554324014291467144646477238464467422645352253054043072408503415623126059018449111807300294890437634529289974129444571536738052570355117041655957194797795932221088165512417385741652358788534138109677638428769384923912855674834081924263955235117285222418082095493531450824685078351263802277062074247864049889090769102738157321783125317563334972475927126639159045005010465255142270934345377339994304284391870997274086299657145887645914183207352738211747434113585868854466417725818033061437465667753585246998223876165557439167293956794262865991380668462719740982987724541500400391567701961940918159642386316128764963374724640309606761513868077290881541455948690259950121789131017262290159942490351322990758776243445625723997047941366665514450305070398888439416362632425588719735162357397479016945380129467671413842072119104000322860831477225418789147099598909139373946098302763513794437681341662578817402330966245646491800413245804870825457441490580402787793311420882850111520005066977852056917452397335125352731022949725920358513273392
decrypt_key = modinv(e, euler_tot) = 97947443900524080191446418200358964894514983896595100917345619492485351014389010789773809219193783476885894363853986839609634323382094519020045017872183892389199029691695425209960304681655760875600420216555449611351057322449998167403127238784464235940520723908120900740270593708738216059614921653939858820884570784133348078569567408195409942197024357650215243834952970787234564579228696916327118249282619782509563249974433386635864110475706385437679778847626962613679407222981079161367874254774380669773556113596975833849765492081560428806779995911549969370859406030380441549344595800788002719550696181409025832199872837747135601303973069391407073831392878046636924273364167788348975547748266210646095491571088300505759549576117346943062604622258200178886908155195598496187856561008219352702078288430556428239639338779175180953310520039842761612618360251012177164137360557331509685869582782421599486453168672995255112754229040993031774366604253249979366988203302275085602294754186912098713790531166873053644862314045105253694994187994721761839377636465577626666568155763150460347189523338307711960573939225206219655060079369394286413391401284211818353269597162262100913482480941739344161165063870167524617918897779369420501512993545
original_message = pow(memos.enc, decrypt_key, n)
Original Message:
544f444f0a2d2d2d2d0a0a2a2053746f7020646f776e6c6f6164696e672052414d20666f722074686520696e7465726e65742e0a2a2052656d6f76652079616b756869746f2066726f6d20746865206e617567687479206b696473206c6973742e0a2a204472696e6b20616c6c20746865206d696c6b3b2065617420616c6c2074686520636f6f6b6965730a2a20446f206e6f7420666f726765742074686520666c61673a20582d4d41537b79616b756869746f5f73686f756c645f6e30745f62335f306e5f7468335f6e4075676874795f6c3173745f393431323832613735643839653038307d0a
Original Message Ascii: TODO ----
- Stop downloading RAM for the internet.
- Remove yakuhito from the naughty kids list.
- Drink all the milk; eat all the cookies
- Do not forget the flag: X-MAS{yakuhito_should_n0t_b3_0n_th3_n@ughty_l1st_941282a75d89e080}
Flag is : X-MAS{yakuhito_should_n0t_b3_0n_th3_n@ughty_l1st_941282a75d89e080}
:D Thank you for reading!