Italian Trulli
Clear the mind

b01lers [ crypto ] Oct 3, 2020

As most blogs look empty in the beginning, here a (kind of) useless blogpost to fill the void!

Given information

They’ve gotten into your mind, but haven’t managed to dive that deep yet. Root them out before it becomes an issue.

$ cat ciphertext-bb416c708f242b0c70d6f2c07d646d9f.txt
Modulus: 98570307780590287344989641660271563150943084591122129236101184963953890610515286342182643236514124325672053304374355281945455993001454145469449640602102808287018619896494144221889411960418829067000944408910977857246549239617540588105788633268030690222998939690024329717050066864773464183557939988832150357227
One factor of N:  9695477612097814143634685975895486365012211256067236988184151482923787800058653259439240377630508988251817608592320391742708529901158658812320088090921919
Public key: 65537
Ciphertext: 75665489286663825011389014693118717144564492910496517817351278852753259053052732535663285501814281678158913989615919776491777945945627147232073116295758400365665526264438202825171012874266519752207522580833300789271016065464767771248100896706714555420620455039240658817899104768781122292162714745754316687483

First steps

The challenge is distributed as a file containing some information that may be used to decipher the given ciphertext

One Shot Solve

As this is an introductory challenge, we can solve it in a fairly strait-foward way, in this case using the RsaCtfTool:

$ ./RsaCtfTool.py -n 102346477809188164149666237875831487276093753138581452189150581288274762371458335130208782251999067431416740623801548745068435494069196452555130488551392351521104832433338347876647247145940791496418976816678614449219476252610877509106424219285651012126290668046420434492850711642394317803367090778362049205437 --uncipher 4458558515804625757984145622008292910146092770232527464448604606202639682157127059968851563875246010604577447368616002300477986613082254856311395681221546841526780960776842385163089662821 -e 3

...

Results for /tmp/tmpxi7twzzn:

Unciphered data :
HEX : 0x666c61677b77335f6e6565645f376f5f67305f6433657033727d
INT (big endian) : 164587995846552213349276905669580061809447554828318448024777341
INT (little endian) : 201584106411901694616549114265403818352500570162482437244939366
STR : b'flag{w3_need_7o_g0_d3ep3r}'

...

As you can see, the ciphertext could be unciphered pretty much the same way as in the Dream Stealing challenge.

Flag

flag{w3_need_7o_g0_d3ep3r}