Data commit

Task/Vigen-re-cipher-Cryptanalysis/Python/vigen-re-cipher-cryptanalysis.py

@@ -0,0 +1,106 @@
+from string import uppercase
+from operator import itemgetter
+
+def vigenere_decrypt(target_freqs, input):
+    nchars = len(uppercase)
+    ordA = ord('A')
+    sorted_targets = sorted(target_freqs)
+
+    def frequency(input):
+        result = [[c, 0.0] for c in uppercase]
+        for c in input:
+            result[c - ordA][1] += 1
+        return result
+
+    def correlation(input):
+        result = 0.0
+        freq = frequency(input)
+        freq.sort(key=itemgetter(1))
+
+        for i, f in enumerate(freq):
+            result += f[1] * sorted_targets[i]
+        return result
+
+    cleaned = [ord(c) for c in input.upper() if c.isupper()]
+    best_len = 0
+    best_corr = -100.0
+
+    # Assume that if there are less than 20 characters
+    # per column, the key's too long to guess
+    for i in xrange(2, len(cleaned) // 20):
+        pieces = [[] for _ in xrange(i)]
+        for j, c in enumerate(cleaned):
+            pieces[j % i].append(c)
+
+        # The correlation seems to increase for smaller
+        # pieces/longer keys, so weigh against them a little
+        corr = -0.5 * i + sum(correlation(p) for p in pieces)
+
+        if corr > best_corr:
+            best_len = i
+            best_corr = corr
+
+    if best_len == 0:
+        return ("Text is too short to analyze", "")
+
+    pieces = [[] for _ in xrange(best_len)]
+    for i, c in enumerate(cleaned):
+        pieces[i % best_len].append(c)
+
+    freqs = [frequency(p) for p in pieces]
+
+    key = ""
+    for fr in freqs:
+        fr.sort(key=itemgetter(1), reverse=True)
+
+        m = 0
+        max_corr = 0.0
+        for j in xrange(nchars):
+            corr = 0.0
+            c = ordA + j
+            for frc in fr:
+                d = (ord(frc[0]) - c + nchars) % nchars
+                corr += frc[1] * target_freqs[d]
+
+            if corr > max_corr:
+                m = j
+                max_corr = corr
+
+        key += chr(m + ordA)
+
+    r = (chr((c - ord(key[i % best_len]) + nchars) % nchars + ordA)
+         for i, c in enumerate(cleaned))
+    return (key, "".join(r))
+
+
+def main():
+    encoded = """
+        MOMUD EKAPV TQEFM OEVHP AJMII CDCTI FGYAG JSPXY ALUYM NSMYH
+        VUXJE LEPXJ FXGCM JHKDZ RYICU HYPUS PGIGM OIYHF WHTCQ KMLRD
+        ITLXZ LJFVQ GHOLW CUHLO MDSOE KTALU VYLNZ RFGBX PHVGA LWQIS
+        FGRPH JOOFW GUBYI LAPLA LCAFA AMKLG CETDW VOELJ IKGJB XPHVG
+        ALWQC SNWBU BYHCU HKOCE XJEYK BQKVY KIIEH GRLGH XEOLW AWFOJ
+        ILOVV RHPKD WIHKN ATUHN VRYAQ DIVHX FHRZV QWMWV LGSHN NLVZS
+        JLAKI FHXUF XJLXM TBLQV RXXHR FZXGV LRAJI EXPRV OSMNP KEPDT
+        LPRWM JAZPK LQUZA ALGZX GVLKL GJTUI ITDSU REZXJ ERXZS HMPST
+        MTEOE PAPJH SMFNB YVQUZ AALGA YDNMP AQOWT UHDBV TSMUE UIMVH
+        QGVRW AEFSP EMPVE PKXZY WLKJA GWALT VYYOB YIXOK IHPDS EVLEV
+        RVSGB JOGYW FHKBL GLXYA MVKIS KIEHY IMAPX UOISK PVAGN MZHPW
+        TTZPV XFCCD TUHJH WLAPF YULTB UXJLN SIJVV YOVDJ SOLXG TGRVO
+        SFRII CTMKO JFCQF KTINQ BWVHG TENLH HOGCS PSFPV GJOKM SIFPR
+        ZPAAS ATPTZ FTPPD PORRF TAXZP KALQA WMIUD BWNCT LEFKO ZQDLX
+        BUXJL ASIMR PNMBF ZCYLV WAPVF QRHZV ZGZEF KBYIO OFXYE VOWGB
+        BXVCB XBAWG LQKCM ICRRX MACUO IKHQU AJEGL OIJHH XPVZW JEWBA
+        FWAML ZZRXJ EKAHV FASMU LVVUT TGK"""
+
+    english_frequences = [
+        0.08167, 0.01492, 0.02782, 0.04253, 0.12702, 0.02228, 0.02015,
+        0.06094, 0.06966, 0.00153, 0.00772, 0.04025, 0.02406, 0.06749,
+        0.07507, 0.01929, 0.00095, 0.05987, 0.06327, 0.09056, 0.02758,
+        0.00978, 0.02360, 0.00150, 0.01974, 0.00074]
+
+    (key, decoded) = vigenere_decrypt(english_frequences, encoded)
+    print "Key:", key
+    print "\nText:", decoded
+
+main()