2015, CTF, Cybercamp

English [Cybercamp 2015] Back on the event

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Hey guys… Cybercamp has just finished! 🙂

There were a lot of challenges, some were really nice, but a good part of them were just full guessing which is really annoying :/

After an entire week (July, 17th to 26th) we ranked 9 out of 879..not so bad isn’t it?
And…we are the 1st non-Spanish team! The second one is only 49th.
Moreover we are proud for having resolved Web 4, only flagged by us!

Our results are:
Crypto: 16/20
Exploit: 2/5
Forensic: 19/27
Reverse: 5/5
Web: 17/18 (there were 20 challenges initially, but two were cancelled)

Write-ups (coming soon):
Crypto: 1 –2 – 3 – 4 – 5 – 6 – 7 – 9  – 11  – 13 – 14 – 15 – 16 – 17 – 19 – 20
Exploit: 1 – 2
Forensic: 1.1 – 1.2 – 1.3 | 2.1 – 2.2 – 2.3 – 2.4 – 2.5 | 3.1 – 3.2 – 3.3 – 3.5 | 4.1 – 4.2 – 4.4 | 5.1 | 7.2 – 7.3 | 8.1
Reverse: 1 – 2 – 3 – 4 – 5
Web: 1  – 2 – 3 – 4 – 5 – 6 – 7 – 8 – 9 – 11 – 12 – 13 – 15 – 16 – 17 – 18 – 19 – 20  (Bonus: 10 cancelled)

See you for next CTF folks !

0x90r00t.

2015, CTF, Cybercamp

English [Cybercamp 2015] [Crypto 1-9] Write Up

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Hi guys, since the first crypto challenges were quite easy, I’ll wrap the first of them in this write-up.

Crypto 1

Ciphered message : DWDFDUIORWDHHXX

This was a really simple Caesar cipher. All letters were shifted 3 times. A became D, W became A and so on.

Deciphered message : ATACARFLOTAEEUU

Crypto 2

Ciphered message : VCXRKFRQLCDLCKZTFCFI

With a Caesar deciphering with a shift of 17 letters :
Deciphered message : ELGATOAZULMULTICOLOR

Crypto 3

Ciphered message : BZHUBTLYVZPTWHYLZFXWLTL

First, we found a custom Caesar cipher, with a shift of 7 letters, giving :

USANUMEROSIMPARESYQPEME

Meaning : Use odd numbers YQPEME

I didn’t understand why they talked about odd numbers, because the last word was a progressive Caesar cipher : Q was shifted by 20 letters, then the shift was increased by 2 for each letter.

Deciphered message : USA NUMEROS IMPARES EUREKA

Crypto 4

Some criminals use a text as a seed for their ciphering keys. Can we find the keys using the following text ? The key words are in bold :

Plantilla: El texto dramático, por lo tanto, es aquel que representa
algún conflicto de la vida a partir del diálogo entre los personajes. La
noción de drama permite nombrar, en forma genérica, a cualquier obra escrita
por un dramaturgo donde los hechos tienen lugar en un espacio y tiempo
determinados.

By looking at their position in the text, we find :

2 3 5 7 11

These are the first prime numbers. If we keep following this logic, we then have :

2 3 5 7 11 13 17 19 23 29 31 37 41 43 47

And by concatenation of the corresponding words, we have the key :

Deciphered key : textodramaticoloesalgundepartirdialogolaengenericaunhechoslugary

Crypto 5

Ciphered message : YUc5c1lXMTFibVJ2

After a double base 64 decode, we get the answer

Deciphered message : holamundo

Crypto 6

a XOR b = 0x35
b XOR C = 0x15

a XOR c = ?

This is some easy XOR calculation.

(a XOR b) XOR (b XOR c) = 0x35 XOR 0x15

a XOR (b XOR b) XOR c = 0x20

a XOR c = 0x20

Crypto 7

Ciphered message : CHECO VERMO ORAAH

These were some basic anagrams.

Deciphered message : COCHE MOVER AHORA

(Move car now)

Crypto 9

Find the following row :
RO: 0000 1000 0100 1010 (Initial seed)
R1: 0001 0000 1001 0100
R2: 0100 0010 0101 0000
R3: 0001 0010 1000 00-0
R4: 0101 0000 0100 0010
R5: 0100 0010 0101 0000
R6: ?

We notice that each row is like the first one, but shifted.

R1 is shifted by 2 on the left

R2 is shifted by 3 on the left

then 5, 8. This is Fibonacci. So next line will be shifted by 13

0000 1000 0100 1010