Deep Cover

Description

As the Viking ship sailed across the vast North Sea, its crew encountered unexpected turbulence in the form of a message. Amidst the rugged expanse of the waters, a messenger bird descended, bearing a weather report inscribed in Cyrillic script. With furrowed brows, the Norsemen deciphered the ominous tidings, seeking the hidden meaning within.

ciphertext.txt

ciphertext.txt

** Vfyhrfz Zftkzh: Skqmkv **

Qkdzmf: ZFNYMHFN

------------------------

Qdanyx: Tfzbknq kg qakv fanbao pfgkzf skzabao hrfa mlkdnx vbhr 30 tfzmfah mryamf kg gldzzbfq. Yskdah 2 hk 4 ms. Vban dt hk 15 us/r. Lkv sbadq 9. Vban mrbll afyz sbadq 14.

Skanyx: Mlkdnx vbhr 30 tfzmfah mryamf kg gldzzbfq fyzlx ba hrf skzabao. Mlfyzbao ba hrf skzabao. Vban dt hk 15 us/r. Rbor sbadq 5. Vban mrbll sbadq 14 ba hrf skzabao yan sbadq 9 ba hrf yghfzakka.

Hdfqnyx: Qdaax. Rbor tldq 2.

Vfnafqnyx: Qdaax. Rbor tldq 4.

Hrdzqnyx: Y gfv mlkdnq. Vban pfmksbao qkdhr 30 us/r yghfz sbnaborh. Lkv sbadq 18. Vban mrbll sbadq 19 hrbq fcfabao yan sbadq 30 kcfzaborh. Zbqu kg gzkqhpbhf.

Gzbnyx: Mlkdnx. 60 tfzmfah mryamf kg lborh qakv ba hrf yghfzakka. Vban qkdhr 40 us/r odqhbao hk 60. Rbor sbadq 7. Vban mrbll sbadq 26 ba hrf skzabao yan sbadq 18 ba hrf yghfzakka.

Qyhdznyx: Rfycx qakv pfobaabao ba hrf skzabao. Yskdah 40 hk 45 ms. Vban akzhrfyqh 30 us/r cbufMHG{6d5hbao_7k_50_US_t3z_r0dz}. Hfstfzyhdzf zbqbao hk sbadq 10 px fcfabao. Vban mrbll afyz sbadq 21.

Solution

We kind of see the flag in the last sentence, but its in incorrect format. Rot ciphers like ROT13, ROT47 didnt work, nor vigenere nor atbash. The given cipher is really big, so the next idea was Frequency Analysis

There's a great tool called quipqiup for this kind of task.

decoded.txt

Flsx isoyvl aows isoyvl vpajwvodv suvoj. Krs Whg.
** Weather Report: Moscow ** 
Source: REDACTED 
------------------------ 
Sunday: Periods of snow ending before morning then cloudy with 30 percent chance of flurries. Amount 2 to 4 cm. Wind up to 15 km/h. Low minus 9. Wind chill near minus 14. 
Monday: Cloudy with 30 percent chance of flurries early in the morning. Clearing in the morning. Wind up to 15 km/h. High minus 5. Wind chill minus 14 in the morning and minus 9 in the afternoon. 
Tuesday: Sunny. High plus 2. 
Wednesday: Sunny. High plus 4. 
Thursday: A few clouds. Wind becoming south 30 km/h after midnight. Low minus 18. Wind chill minus 19 this evening and minus 30 overnight. Risk of frostbite. 
Friday: Cloudy. 60 percent chance of light snow in the afternoon. Wind south 40 km/h gusting to 60. High minus 7. Wind chill minus 26 in the morning and minus 18 in the afternoon. 
Saturday: Heavy snow beginning in the morning. Amount 40 to 45 cm. Wind northeast 30 km/h vikeCTF{6u5ting_7o_50_KM_p3r_h0ur}. Temperature rising to minus 10 by evening. Wind chill near minus 21.

Flag: vikeCTF{6u5ting_7o_50_KM_p3r_h0ur}