picoCTF (Cryptography) - Writeup

A writeup for picoGym’s cryptography challenges.

Crypto

The Numbers

Flag: picoCTF{thenumbersmason}

The numbers… what do they mean?

Input

16 9 3 15 3 20 6 20 8 5 14 21 13 2 5 18 19 13 1 19 15 14

CyberChef’s Recipe

A1Z26_Cipher_Decode('Space')

Output

picoctfthenumbersmason

13

Flag: picoCTF{not_too_bad_of_a_problem}

Cryptography can be easy, do you know what ROT13 is? cvpbPGS{abg_gbb_onq_bs_n_ceboyrz}

CyberChef’s Recipe

ROT13(true,true,false,13)

Mod 26

Flag: picoCTF{next_time_I'll_try_2_rounds_of_rot13_TLcKBUdK}

Cryptography can be easy, do you know what ROT13 is? cvpbPGS{arkg_gvzr_V’yy_gel_2_ebhaqf_bs_ebg13_GYpXOHqX}

CyberChef’s Recipe

ROT13(true,true,false,13)

interencdec

Flag: picoCTF{caesar_d3cr9pt3d_86de32d2}

Can you get the real meaning from this file.

$ cat enc_flag
YidkM0JxZGtwQlRYdHFhR3g2YUhsZmF6TnFlVGwzWVROclh6ZzJhMnd6TW1zeWZRPT0nCg==

From_Base64('A-Za-z0-9+/=',true,false)
Find_/_Replace({'option':'Regex','string':'b\''},'',true,false,true,false)
Find_/_Replace({'option':'Regex','string':'\''},'',true,false,true,false)
From_Base64('A-Za-z0-9+/=',true,false)
ROT13(true,true,false,19)

rotation

Flag: picoCTF{r0tat1on_d3crypt3d_4c71f5b0}

You will find the flag after decrypting this file

Bruteforce rotation using CyberChef, key=18.

Vigenere

Flag: picoCTF{D0NT_US3_V1G3N3R3_C1PH3R_ae82272q}

Can you decrypt this message?

Use dcode to decode the message. By knowing picoCTF as the flag format, we can acquire the key by bruteforcing.

substitution0

Flag: picoCTF{5UB5717U710N_3V0LU710N_03055505}

A message has come in but it seems to be all scrambled. Luckily it seems to have the key at the beginning. Can you crack this substitution cipher?

Use this tool to automatically break the substitution cipher.

substitution1

Flag: picoCTF{FR3QU3NCY_4774CK5_4R3_C001_4871E6FB}

A second message has come in the mail, and it seems almost identical to the first one. Maybe the same thing will work again.

Use CyberChef to manually break the substitution cipher.

substitution2

Flag: picoCTF{N6R4M_4N41Y515_15_73D10U5_8E1BF808}

It seems that another encrypted message has been intercepted. The encryptor seems to have learned their lesson though and now there isn’t any punctuation! Can you still crack the cipher?

Use this tool to automatically break the substitution cipher.

caesar

Flag: picoCTF{crossingtherubiconzaqjsscr}

Decrypt this message.

Use CyberChef to bruteforce the cipher. It turns out the flag is encrypted using key 25.

morse-code

Flag: picoCTF{WH47_H47H_90D_W20U9H7}

Morse code is well known. Can you decrypt this? Download the file here. Wrap your answer with picoCTF{}, put underscores in place of pauses, and use all lowercase.

Use this tool to automatically decode the morse code in the wav file.