+ - Solution non-frequency analysis approach

+```Python

+import string

+from collections import Counter

+from itertools import cycle

+

+def xor_mb(message, key):

+        return''.join(chr(ord(m_byte)^ord(k_byte)) for m_byte,k_byte in zip(message, cycle(key)))

+

+printset = set(string.printable)

+messages = open("4.txt", 'r').readlines()

+

+for line in messages:

+    message = line.rstrip().decode('hex')

+    cnt = Counter(message)

+    for vv in cnt.most_common(3):

+            for char in "ETAOINSHRDLU".lower():

+                key = chr(ord(vv[0]) ^ ord(char))

+                temp = xor_mb(message, key)

+                if set(temp).issubset(printset) and temp[-1] == "\n":

+                    print key, temp

+```

+

+

+ - https://dbjergaard.github.io/posts/matasano_set_1.html

+ - [Pearson's chi-squared test](https://en.wikipedia.org/wiki/Pearson%27s_chi-squared_test) 

+ - [Chi-square distribution introduction | Probability and Statistics | Khan Academy](https://www.youtube.com/watch?v=dXB3cUGnaxQ)

+### Reads (no cheats)

+ - https://dbjergaard.github.io/posts/matasano_set_1.html

+

+

+### Challenge 4  - Detect single-character XOR

+```Python 

+from collections import Counter

+message = "1b37373331363f78151b7f2b783431333d78397828372d363c78373e783a393b3736".decode('hex')

+cnt = Counter(message)

+cnt.most_common(3)

+for vv in cnt.most_common(7):

+	for char in "ETAOIN SHRDLU".lower():

+		key = chr(ord(vv[0]) ^ ord(char))

+		print key, xor_mb(message, key)