Another update from ingydotnet^djgoku

Task/Vigen-re-cipher-Cryptanalysis/Julia/vigen-re-cipher-cryptanalysis.julia

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+# ciphertext block {{{1
+const ciphertext = filter(isalpha, """
+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
+""")
+# }}}
+
+# character frequencies {{{1
+const letters = Dict{Char, Float32}(
+    'E' => 12.702,
+    'T' => 9.056,
+    'A' => 8.167,
+    'O' => 7.507,
+    'I' => 6.966,
+    'N' => 6.749,
+    'S' => 6.327,
+    'H' => 6.094,
+    'R' => 5.987,
+    'D' => 4.253,
+    'L' => 4.025,
+    'C' => 2.782,
+    'U' => 2.758,
+    'M' => 2.406,
+    'W' => 2.361,
+    'F' => 2.228,
+    'G' => 2.015,
+    'Y' => 1.974,
+    'P' => 1.929,
+    'B' => 1.492,
+    'V' => 0.978,
+    'K' => 0.772,
+    'J' => 0.153,
+    'X' => 0.150,
+    'Q' => 0.095,
+    'Z' => 0.074)
+const digraphs = Dict{String, Float32}(
+    "TH" => 15.2,
+    "HE" => 12.8,
+    "IN" => 9.4,
+    "ER" => 9.4,
+    "AN" => 8.2,
+    "RE" => 6.8,
+    "ND" => 6.3,
+    "AT" => 5.9,
+    "ON" => 5.7,
+    "NT" => 5.6,
+    "HA" => 5.6,
+    "ES" => 5.6,
+    "ST" => 5.5,
+    "EN" => 5.5,
+    "ED" => 5.3,
+    "TO" => 5.2,
+    "IT" => 5.0,
+    "OU" => 5.0,
+    "EA" => 4.7,
+    "HI" => 4.6,
+    "IS" => 4.6,
+    "OR" => 4.3,
+    "TI" => 3.4,
+    "AS" => 3.3,
+    "TE" => 2.7,
+    "ET" => 1.9,
+    "NG" => 1.8,
+    "OF" => 1.6,
+    "AL" => 0.9,
+    "DE" => 0.9,
+    "SE" => 0.8,
+    "LE" => 0.8,
+    "SA" => 0.6,
+    "SI" => 0.5,
+    "AR" => 0.4,
+    "VE" => 0.4,
+    "RA" => 0.4,
+    "LD" => 0.2,
+    "UR" => 0.2)
+const trigraphs = Dict{String, Float32}(
+    "THE" => 18.1,
+    "AND" => 7.3,
+    "ING" => 7.2,
+    "ION" => 4.2,
+    "ENT" => 4.2,
+    "HER" => 3.6,
+    "FOR" => 3.4,
+    "THA" => 3.3,
+    "NTH" => 3.3,
+    "INT" => 3.2,
+    "TIO" => 3.1,
+    "ERE" => 3.1,
+    "TER" => 3.0,
+    "EST" => 2.8,
+    "ERS" => 2.8,
+    "HAT" => 2.6,
+    "ATI" => 2.6,
+    "ATE" => 2.5,
+    "ALL" => 2.5,
+    "VER" => 2.4,
+    "HIS" => 2.4,
+    "HES" => 2.4,
+    "ETH" => 2.4,
+    "OFT" => 2.2,
+    "STH" => 2.1,
+    "RES" => 2.1,
+    "OTH" => 2.1,
+    "ITH" => 2.1,
+    "FTH" => 2.1,
+    "ONT" => 2.0)
+# 1}}}
+
+function decrypt(enc::ASCIIString, key::ASCIIString)
+    const enclen = length(enc)
+    const keylen = length(key)
+
+    if keylen < enclen
+        key = (key^(div(enclen - keylen, keylen) + 2))[1:enclen]
+    end
+
+    msg = Array(Char, enclen)
+
+    for i=1:enclen
+        msg[i] = Char((Int(enc[i]) - Int(key[i]) + 26) % 26 + 65)
+    end
+
+    msg::Array{Char, 1}
+end
+
+function cryptanalyze(enc::ASCIIString; maxkeylen::Integer = 20)
+    const enclen = length(enc)
+    maxkey = ""
+    maxdec = ""
+    maxscore = 0.0
+
+    for keylen=1:maxkeylen
+        key = Array(Char, keylen)
+        idx = filter(x -> x % keylen == 0, 1:enclen) - keylen + 1
+
+        for i=1:keylen
+            maxsubscore = 0.0
+
+            for j='A':'Z'
+                subscore = 0.0
+
+                for k in decrypt(enc[idx], ascii(string(j)))
+                    subscore += get(letters, k, 0.0)
+                end
+
+                if subscore > maxsubscore
+                    maxsubscore = subscore
+                    key[i] = j
+                end
+            end
+
+            idx += 1
+        end
+
+        key = join(key)
+        const dec = decrypt(enc, key)
+        score = 0.0
+
+        for i in dec
+            score += get(letters, i, 0.0)
+        end
+
+        for i=1:enclen - 2
+            const digraph = string(dec[i], dec[i + 1])
+            const trigraph = string(dec[i], dec[i + 1], dec[i + 2])
+
+            if haskey(digraphs, digraph)
+                score += 2 * get(digraphs, digraph, 0.0)
+            end
+
+            if haskey(trigraphs, trigraph)
+                score += 3 * get(trigraphs, trigraph, 0.0)
+            end
+        end
+
+        if score > maxscore
+            maxscore = score
+            maxkey = key
+            maxdec = dec
+        end
+    end
+
+    (maxkey, join(maxdec))::Tuple{ASCIIString, ASCIIString}
+end
+
+key, dec = cryptanalyze(ciphertext)
+println("key: ", key, "\n\n", dec)
+
+# post-compilation profiling run
+gc()
+t = @elapsed cryptanalyze(ciphertext)
+println("\nelapsed time: ", t, " seconds")