Title : [writeups] CSAW 2015 - Crypto 50 - whiter0se
Released : 2015-09-25 17:29:24 -0400
Viewed : 1072

Hi halo there, this is my first article that didn't use my native language. So if the language is less precise, please be advised.

This challenge is about cryptography. When i open it, i got this task

Note: The flag is the entire thing decrypted

eps1.7_wh1ter0se_2b007cf0ba9881d954e85eb475d0d5e4.m4v

I download the decrypted file from the link, and i got this hash:

EOY XF, AY VMU M UKFNY TOY YF UFWHYKAXZ EAZZHN. UFWHYKAXZ ZNMXPHN. UFWHYKAXZ EHMOYACOI. VH'JH EHHX CFTOUHP FX VKMY'U AX CNFXY FC OU. EOY VH KMJHX'Y EHHX IFFQAXZ MY VKMY'U MEFJH OU.

i try to decrypt this hash using some rotation but certainly not as easy as it :p

So I tried to figure it manually

The method I use is to consider "if there is one letter alone, surely it is a word suffix as an "A", and we get our first character subsitution.

M UKFNY = A UKFNY

first try, all hash looks like this

EOY XF, AY VAU A UKFNY TOY YF UFWHYKAXZ EAZZHN. UFWHYKAXZ ZNAXPHN. UFWHYKAXZ EHAOYACOI. VH'JH EHHX CFTOUHP FX VKAY'U AX CNFXY FC OU. EOY VH KAJHX'Y EHHX IFFQAXZ AY VKAY'U AEFJH OU.

but still not readable :p

Second charater. Now let's look at the word "EHHX", it could be "LOOK" "SEEN" or "DEEP" . But, let's assume it's a vowel. And for the second try, we substitute "H" to "E".

EOY XF, AY VAU A UKFNY TOY YF UFWEYKAXZ EAZZEN. UFWEYKAXZ ZNAXPEN. UFWEYKAXZ EEAOYACOI. VE'JE EEEX CFTOUEP FX VKAY'U AX CNFXY FC OU. EOY VE KAJEX'Y EEEX IFFQAXZ AY VKAY'U AEFJE OU.

still not readable :)

Now, let's looking for this word "VE'JE" and i am absolutely sure this word are "WE'VE" :)

so, lets substitute V to W, and J to V

EOY XF, AY WAU A UKFNY TOY YF UFWEYKAXZ EAZZEN. UFWEYKAXZ ZNAXPEN. UFWEYKAXZ EEAOYACOI. WE'VE EEEX CFTOUEP FX WKAY'U AX CNFXY FC OU. EOY WE KAVEX'Y EEEX IFFQAXZ AY WKAY'U AEFVE OU.

and the word "WAU" looks like "WAS", then substitute it again, U=S

EOY XF, AY WAS A SKFNY TOY YF SFWEYKAXZ EAZZEN. SFWEYKAXZ ZNAXPEN. SFWEYKAXZ EEAOYACOI. WE'VE EEEX CFTOSEP FX WKAY'S AX CNFXY FC OS. EOY WE KAVEX'Y EEEX IFFQAXZ AY WKAY'S AEFVE OS.

i think i;m on the right track. Next, i'll guess OS as US. So, O=U

EUY XF, AY WAS A SKFNY TUY YF SFWEYKAXZ EAZZEN. SFWEYKAXZ ZNAXPEN. SFWEYKAXZ EEAUYACUI. WE'VE EEEX CFTUSEP FX WKAY'S AX CNFXY FC US. EUY WE KAVEX'Y EEEX IFFQAXZ AY WKAY'S AEFVE US.

still, now looks at this word "EEAUYACUI" it's looks like "BEAUTIFUL". One more right track :)

But for this challenge, I do not really do it manually. Because it is really a waste of time. So, i coding it. Yarp. I made my own decryptor for this kind of Manual Substitution Challenges.

csaw2015-crypto50.png

and after all, i got the flag

BUT NO, IT WAS A SHORT CUT TO SOMETHING BIGGER. SOMETHING GRANDER. SOMETHING BEAUTIFUL. WE'VE BEEN FOCUSED ON WHAT'S IN FRONT OF US. BUT WE HAVEN'T BEEN LOOKING AT WHAT'S ABOVE US.

:)