Problem Statment:

Now that you know about RSA can you help us decrypt this ciphertext? We don't have the decryption key but something about those values looks funky..

Solution :

In ciphertext file we were given :

N: 374159235470172130988938196520880526947952521620932362050308663243595788308583992120881359365258949723819911758198013202644666489247987314025169670926273213367237020188587742716017314320191350666762541039238241984934473188656610615918474673963331992408750047451253205158436452814354564283003696666945950908549197175404580533132142111356931324330631843602412540295482841975783884766801266552337129105407869020730226041538750535628619717708838029286366761470986056335230171148734027536820544543251801093230809186222940806718221638845816521738601843083746103374974120575519418797642878012234163709518203946599836959811

e: 3

ciphertext (c): 2205316413931134031046440767620541984801091216351222789180582564557328762455422721368029531360076729972211412236072921577317264715424950823091382203435489460522094689149595951010342662368347987862878338851038892082799389023900415351164773

It is Low public exponent attack.You can find the python script here.

After running python file flag recieved :
picoCTF{e_w4y_t00_sm411_81b6559f}

Original writeup (https://github.com/d4rkvaibhav/PICOCTF-2018/blob/master/Cryptography/SAFERSA/README.md).