picoctf2019-writeup

picoCTF2019 writeup

Project maintained by johantannh Hosted on GitHub Pages — Theme by mattgraham

The-Numbers

Points: 50

Problem

The numbers… what do they mean?

Hint

The flag is in the format PICOCTF{}

Solution

The image show a bunch of number align in the following format

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

The number above is encrypted using a Substitution Cipher based on Letter Number (A1Z26) A=1, B=2, C=3…..

16 9 3 15 3 20 6 => PICOCTF

20 8 5 14 21 13 2 5 18 19 13 1 19 15 14 => THENUMBERSMASON

Flag

PICOCTF{THENUMBERSMASON}

13

Points: 100

Problem

Cryptography can be easy, do you know what ROT13 is?

cvpbPGS{abg_gbb_onq_bs_n_ceboyrz}

Hint

This can be solved online if you don’t want to do it by hand!

Solution

The encrypted code above can be decrypted online here using the ROT13 encryptor & decryptor

cvpbPGS{abg_gbb_onq_bs_n_ceboyrz} => picoCTF{not_too_bad_of_a_problem}

Flag

picoCTF{not_too_bad_of_a_problem}

caesar

Points: 100

Problem

Decrypt this message . You can find the ciphertext in /problems/caesar_0_22aa542fadadcc37b6ec6037c493ec9f on the shell server.

picoCTF{jyvzzpunaolybipjvunfzpthre}

Hint

caesar cipher tutorial

Solution

The encrypted code above can be decrypted online here using the Caesar-Cipher . Brute Force Attack can be applied to guess all possible combination for the shifting of the letter.

picoCTF{jyvzzpunaolybipjvunfzpthre} => picoCTF{crossingtherubicongysimakx}

Flag

picoCTF{crossingtherubicongysimakx}

Flags

Points: 200

Problem

What do the flags mean?

Hint

The flag is in the format PICOCTF{}

Solution

The flag show is encoded in NATO phonetic alphabet, codes & signals. This can be seen below

The Code :

Flag

Encryption Table :

Table

Flag

PICOCTF{F1AG5AND5TUFF}

Mr-Worldwide

Points: 200

Problem

A musician left us a message. What’s it mean?

Hint

Nil

Solution

Arrange the coordinates. put each one into google map

picoCTF{
(35.028309, 135.753082)
(46.469391, 30.740883)
(39.758949, -84.191605)
(41.015137, 28.979530)
(24.466667, 54.366669)
(3.140853, 101.693207)
_
(9.005401, 38.763611)
(-3.989038, -79.203560)
(52.377956, 4.897070)
(41.085651, -73.858467)
(57.790001, -152.407227)
(31.205753, 29.924526)
}

Paste each coordinate in google map. Copy the address for each coordinate and notice the city for each coordinate. Take the first letter of each city and put together it forms the words.

picoCTF{
2QH3+86 Kyoto, Japan
FP9R+Q9 Odesa, Odessa Oblast, Ukraine
QR55+H9 Dayton, Ohio, USA
2X8H+3R Istanbul(Eminönü, Rüstem Paşa, Fatih/İstanbul, Turkey)
F988+MM Abu Dhabi - United Arab Emirates
4MRV+87 Kuala Lumpur, Federal Territory of Kuala Lumpur, Malaysia
_
2Q47+5C Addis Ababa, Ethiopia
2Q6W+9H Loja, Ecuador
9VHW+5R Amsterdam, Netherlands
34PR+7J Sleepy Hollow, New York, USA
QHRV+24 Kodiak, Alaska, USA
6W4F+8R Alexandria, Egypt
}

Flag

picoCTF{KODIAK_ALASKA}

Tapping

Points: 200

Problem

Theres tapping coming in from the wires. What’s it saying nc 2019shell1.picoctf.com 37920.

Hint

What kind of encoding uses dashes and dots? The flag is in the format PICOCTF{}

Solution

  1. Run nc 2019shell1.picoctf.com 37920
  2. Get the flag and use an online morse code decoder to decode the flag.

Flag

PICOCTF{M0RS3C0D31SFUN3960854397}

la-cifra-de

Points: 200

Problem

I found this cipher in an old book. Can you figure out what it says? Connect with nc 2019shell1.picoctf.com 60147

Hint

There are tools that make this easy.

Perhaps looking at history will help

Solution

Ciphertext given is shown below. Apparently it is encoded by Vigenere cipher encryption. To solve this it can be easily brute-force by using online tools such as this.

Cipher Text

Ne iy nytkwpsznyg nth it mtsztcy vjzprj zfzjy rkhpibj nrkitt ltc tnnygy ysee itd tte cxjltk

Ifrosr tnj noawde uk siyyzre, yse Bnretèwp Cousex mls hjpn xjtnbjytki xatd eisjd

Iz bls lfwskqj azycihzeej yz Brftsk ip Volpnèxj ls oy hay tcimnyarqj dkxnrogpd os 1553 my Mnzvgs Mazytszf Merqlsu ny hox moup Wa inqrg ipl. Ynr. Gotgat Gltzndtg Gplrfdo 

Ltc tnj tmvqpmkseaznzn uk ehox nivmpr g ylbrj ts ltcmki my yqtdosr tnj wocjc hgqq ol fy oxitngwj arusahje fuw ln guaaxjytrd catizm tzxbkw zf vqlckx hizm ceyupcz yz tnj fpvjc hgqqpohzCZK{m311a50_0x_a1rn3x3_h1ah3xfmel1g3m}

Tnj qixxe wkqw-duhfmkseej ipsiwtpznzn uk l puqjarusahjeii htpnjc hubpvkw, hay rldk fcoaso 1467 be Qpot Gltzndtg Fwbkwei.

Zmp Volpnèxj Nivmpr ox ehkwpfuwp surptorps ifwlki ehk Fwbkwei Jndc uw Llhjcto Htpnjc.

It 1508, Ozhgsyey Ycizmpmozd itapnzjo tnj do-ifwlki eahzwa xjntg (f xazwtx uk dhokeej fwpnfmezx) ehgy
hoaqo lgypr hj l cxneiifw curaotjyt uk ehk Atgksèce Inahkw.

Merqlsu’x deityd htzkrje avupaxjo it 1555 fd a itytosfaznzn uk ehk ktryy. Ehk qzwkw saraps uk ehk fwpnfmezx lrk szw ymtfzjo rklflgwwy,
hze tnj llvmlbkyd ati ehk nydkc wezypry fce sniej gj mkfys uk l mtjxotnn kkd ahxfde, cmtcn hln hj oilkprkse woys eghs cuwceyuznjjyt.

Encryption Key Brute-Force

flag(Key)

Plain Text

It is interesting how in history people often receive credit for things they did not create

During the course of history, the Vigenère Cipher has been reinvented many times

It was falsely attributed to Blaise de Vigenère as it was originally described in 1553 by Giovan Battista Bellaso in his book La cifra del. Sig. Giovan Battista Bellaso 

For the implementation of this cipher a table is formed by sliding the lower half of an ordinary alphabet for an apparently random number of places with respect to the upper halfpicoCTF{b311a50_0r_v1gn3r3_c1ph3rabef1b3b}

The first well-documented description of a polyalphabetic cipher however, was made around 1467 by Leon Battista Alberti.

The Vigenère Cipher is therefore sometimes called the Alberti Disc or Alberti Cipher.

In 1508, Johannes Trithemius invented the so-called tabula recta (a matrix of shifted alphabets) that would later be a critical
component of the Vigenère Cipher.

Bellaso’s second booklet appeared in 1555 as a continuation of the first. The lower halves of the alphabets are now shifted regularly,
but the alphabets and the index letters are mixed by means of a mnemonic key phrase, which can be different with each correspondent.

Flag

picoCTF{b311a50_0r_v1gn3r3_c1ph3rabef1b3b}

rsa-pop-quiz

Points: 200

Problem

Class, take your seats! It’s PRIME-time for a quiz… nc 2019shell1.picoctf.com 48028

Hint

RSA Info

Solution

  1. rsa-calculator
  2. toitient-calculator

Steps to encode/decode RSA

  1. Find N as a product of two prime numbers p and q. N = p*q

Concepts

  1. Euler’s totient function ϕ(n) - positive integers up to n that are relatively prime to n. Simply put it, no GCD between 2 numbers(except 1) means they are relatively prime.
    • if n = 9, ϕ(9) = { 1, 2, 4, 5, 7, 8 } = 6
    • if n = 16, ϕ(16) = { 1, 3, 5, 7, 9, 11, 13, 15 } = 9 2.

      Flag

      Flag

waves over lambda

Points: 300

Problem

We made alot of substitutions to encrypt this. Can you decrypt it? Connect with nc 2019shell1.picoctf.com 21903.

Hint

Flag is not in the usual flag format

Solution

Ciphertext given is shown below. Apparently it is encoded by substitution cipher encryption. To solve this it can be easily brute-force by using online tools such as this or this.

Cipher Text

-------------------------------------------------------------------------------
vhweytfl bjyj ql ghxy sote - syjrxjwvg_ql_v_hpjy_otikmt_powbwtllfi 
-------------------------------------------------------------------------------
nj njyj whf ixvb ihyj fbtw t rxtyfjy hs tw bhxy hxf hs hxy lbqu fqoo nj ltn bjy lqwa, 
twm fbjw q xwmjylfhhm shy fbj sqylf fqij nbtf ntl ijtwf kg t lbqu shxwmjyqwe qw fbj ljt.  
q ixlf tvawhnojmej q btm btymog jgjl fh ohha xu nbjw fbj ljtijw fhom ij lbj ntl lqwaqwe; 
shy syhi fbj ihijwf fbtf fbjg ytfbjy uxf ij qwfh fbj khtf fbtw fbtf q iqebf kj ltqm fh eh qw, 
ig bjtyf ntl, tl qf njyj, mjtm nqfbqw ij, utyfog nqfb syqebf, utyfog nqfb bhyyhy hs iqwm, 
twm fbj fbhxebfl hs nbtf ntl gjf kjshyj ij.

Encryption Key Brute-Force

This clear text … abcdefghijklmnopqrstuvwxyz

maps to this cipher text… tkvmjsebqcaoiwhurylfxpnzgd(Key)

Plain Text

-------------------------------------------------------------------------------
congrats here is your flag - frequency_is_c_over_lambda_vlnhnasstm 
-------------------------------------------------------------------------------
we were not much more than a quarter of an hour out of our ship till we saw her sink, 
and then i understood for the first time what was meant by a ship foundering in the sea.  
i must acknowledge i had hardly eyes to look up when the seamen told me she was sinking; 
for from the moment that they rather put me into the boat than that i might be said to go in, 
my heart was, as it were, dead within me, partly with fright, partly with horror of mind, 
and the thoughts of what was yet before me.

Flag

picoCTF{frequency_is_c_over_lambda_vlnhnasstm}