Crypto 11

s=not(t)
s= a xor b
t= b xor c
a=1010

c = ?

This was some easy XOR calculation too :

s xor t = a xor (b xor b) xor c
s xor t = a xor c
s xor t = 1010 xor c
s xor t = c xor 1010

But since s = not(t)
s xor t = 1111

We then have

1111 = c xor 1010

So

c = 0101
Continue reading [Cybercamp 2015] [Crypto 11-19] Write Up →

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