some small fixes

Cryptography/RotationCiphers/caesarCipher.py

@@ -0,0 +1,85 @@
+#!/usr/bin/env python
+
+
+__author__ = "bt3gl"
+
+
+import string
+
+
+FREQ_ENGLISH = [0.0749, 0.0129, 0.0354, 0.0362, 0.1400, 0.0218, 0.0174, 0.0422, 0.0665, 0.0027, 0.0047, 0.0357,
+           0.0339, 0.0674, 0.0737, 0.0243, 0.0026, 0.0614, 0.0695, 0.0985, 0.0300, 0.0116, 0.0169, 0.0028,
+           0.0164, 0.0004]
+
+
+
+def delta(freq_word, freq_eng):
+    # zip together the value from the text and the value from FREQ_EdiffGlist_freqISH
+    diff = 0.0
+    for a, b in zip(freq_word, freq_eng):
+        diff += abs(a - b)
+    return diff
+
+
+
+def cipher(msg, key):
+    # Make the cipher
+    dec = ''
+    for c in msg.lower():
+        if 'a' <= c <= 'z':
+             dec += chr(ord('a') + (ord(c) - ord('a') + key) % 26)
+        else:
+             dec += c
+    return dec
+
+
+
+def frequency(msg):
+    # Compute the word frequencies
+    dict_freq = dict([(c,0) for c in string.lowercase])
+    diff = 0.0
+    for c in msg:
+        if 'a'<= c <= 'z':
+            diff += 1
+            dict_freq[c] += 1
+    list_freq = dict_freq.items()
+    list_freq.sort()
+    return [b / diff for (a, b) in list_freq]
+
+
+
+def decipher(msg):
+    # Decipher by frequency
+    min_delta = 1000
+    best_rotation = 0
+    freq = frequency(msg)
+    for key in range(26):
+        d = delta(freq, FREQ_ENGLISH)
+        if d < min_delta:
+            min_delta = d
+            best_rotation = key
+    return cipher(msg, -best_rotation)
+
+
+
+def decipher_simple(msg):
+    # very smart way of solving using translate and maketrans methods
+    diff = (ord('t') - ord(s[0])) % 26
+    x = string.ascii_lowercase
+    x = x[diff:] + x[:diff]
+    ans = string.translate(s,string.maketrans(string.ascii_lowercase,x))
+    return ans
+
+
+
+if __name__ == '__main__':
+
+    key = 13
+    text = 'hacker school is awesome!'
+    cip = cipher(text, key)
+    dec = decipher(cip)
+
+    print "Cipher: " + cip
+    print "Decipher: " + dec
+
+    assert(text == dec)