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DragonSector Crypto 100

In this task we have to win a lottery game: Basically each coupon costs $5 and we have $100 to spend. If we try to withdraw our money we get the amount of money we need to get our flag: To show they are playing fairly, the give you a verification id that its the value you have to guess concatenated with a random salt to reach the AES 16 bytes block that is used to encrypt the string.

NuitDuHack 2014 Crypto Write Ups

Carbonara We are given the following ciphertext: %96 7=28 [email protected] E9:D 492= :D iQx>[email protected] xF=:FD r26D2C s:GFDQ] A simple shift shows interesting results: ciphertext = "%96 7=28 [email protected] E9:D 492= :D iQx>[email protected] xF=:FD r26D2C s:GFDQ]" size = len(ciphertext) for i in range(0,100): result="" for c in ciphertext: if ord(c) > 126 or ord(c) < 33: result += c else: first = ord(c)+i if first > 90: first = 64 + (first - 90) result += chr(first) print(result) Here is were the history classes prove valuable, flag is:

#hackyou2014 Crypto400 write-up

In this level we are said that: We have intercepted communication in a private network. It is used a strange protocol based on RSA cryptosystem. Can you still prove that it is not secure enough and get the flag? We are given a pcap file with a bunch of transmissions generated with this script: #!/usr/bin/python import sys import struct import zlib import socket class Client: def __init__(self, ip): #init self.

#hackyou2014 Crypto300 write-up

In this level we are presented with a crypto system based on Matrix operations: #!/usr/bin/python import random from struct import pack def Str2matrix(s): #convert string to 4x4 matrix return [map(lambda x : ord(x), list(s[i:i+4])) for i in xrange(0, len(s), 4)] def Matrix2str(m): #convert matrix to string return ''.join(map(lambda x : ''.join(map(lambda y : pack('!H', y), x)), m)) def Generate(password): #generate key matrix random.seed(password) return [[random.randint(0,64) for i in xrange(4)] for j in xrange(4)] def Multiply(A,B): #multiply two 4x4 matrix C = [[0 for i in xrange(4)] for j in xrange(4)] for i in xrange(4): for j in xrange(4): for k in xrange(4): C[i][j] += A[i][k] * B[k][j] return C def Encrypt(fname): #encrypt file key = Generate('') data = open(fname, 'rb').

#hackyou2014 Crypto200 write-up

In this level we are said that our challange is login with administrator role in a service listening on hackyou2014tasks.ctf.su 7777 We are given the following source code: #!/usr/bin/python from math import sin from urlparse import parse_qs from base64 import b64encode from base64 import b64decode from re import match SALT = '' USERS = set() KEY = ''.decode('hex') def xor(a, b): return ''.join(map(lambda x : chr(ord(x[0]) ^ ord(x[1])), zip(a, b * 100))) def hashme(s): #my secure hash function def F(X,Y,Z): return ((~X & Z) | (~X & Z)) & 0xFFFFFFFF def G(X,Y,Z): return ((X & Z) | (~Z & Y)) & 0xFFFFFFFF def H(X,Y,Z): return (X ^ Y ^ Y) & 0xFFFFFFFF def I(X,Y,Z): return (Y ^ (~Z | X)) & 0xFFFFFFFF def ROL(X,Y): return (X << Y | X >> (32 - Y)) & 0xFFFFFFFF A = 0x67452301 B = 0xEFCDAB89 C = 0x98BADCFE D = 0x10325476 X = [int(0xFFFFFFFF * sin(i)) & 0xFFFFFFFF for i in xrange(256)] for i,ch in enumerate(s): k, l = ord(ch), i & 0x1f A = (B + ROL(A + F(B,C,D) + X[k], l)) & 0xFFFFFFFF B = (C + ROL(B + G(C,D,A) + X[k], l)) & 0xFFFFFFFF C = (D + ROL(C + H(D,A,B) + X[k], l)) & 0xFFFFFFFF D = (A + ROL(D + I(A,B,C) + X[k], l)) & 0xFFFFFFFF return ''.

#hackyou2014 Crypto100 write-up

In this level we are asked to break a code and decrypt msg002.enc. We are given the encryptor code without the key: #include <stdlib.h> #include <stdio.h> #include <string.h> int main(int argc, char **argv) { if (argc != 3) { printf("USAGE: %s INPUT OUTPUT\n", argv[0]); return 0; } FILE* input = fopen(argv[1], "rb"); FILE* output = fopen(argv[2], "wb"); if (!input || !output) { printf("Error\n"); return 0; } char k[] = "CENSORED"; char c, p, t = 0; int i = 0; while ((p = fgetc(input)) !