102 lines
3.3 KiB
Text
102 lines
3.3 KiB
Text
// version 1.1.3
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val encoded =
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"MOMUD EKAPV TQEFM OEVHP AJMII CDCTI FGYAG JSPXY ALUYM NSMYH" +
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"VUXJE LEPXJ FXGCM JHKDZ RYICU HYPUS PGIGM OIYHF WHTCQ KMLRD" +
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"ITLXZ LJFVQ GHOLW CUHLO MDSOE KTALU VYLNZ RFGBX PHVGA LWQIS" +
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"FGRPH JOOFW GUBYI LAPLA LCAFA AMKLG CETDW VOELJ IKGJB XPHVG" +
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"ALWQC SNWBU BYHCU HKOCE XJEYK BQKVY KIIEH GRLGH XEOLW AWFOJ" +
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"ILOVV RHPKD WIHKN ATUHN VRYAQ DIVHX FHRZV QWMWV LGSHN NLVZS" +
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"JLAKI FHXUF XJLXM TBLQV RXXHR FZXGV LRAJI EXPRV OSMNP KEPDT" +
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"LPRWM JAZPK LQUZA ALGZX GVLKL GJTUI ITDSU REZXJ ERXZS HMPST" +
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"MTEOE PAPJH SMFNB YVQUZ AALGA YDNMP AQOWT UHDBV TSMUE UIMVH" +
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"QGVRW AEFSP EMPVE PKXZY WLKJA GWALT VYYOB YIXOK IHPDS EVLEV" +
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"RVSGB JOGYW FHKBL GLXYA MVKIS KIEHY IMAPX UOISK PVAGN MZHPW" +
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"TTZPV XFCCD TUHJH WLAPF YULTB UXJLN SIJVV YOVDJ SOLXG TGRVO" +
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"SFRII CTMKO JFCQF KTINQ BWVHG TENLH HOGCS PSFPV GJOKM SIFPR" +
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"ZPAAS ATPTZ FTPPD PORRF TAXZP KALQA WMIUD BWNCT LEFKO ZQDLX" +
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"BUXJL ASIMR PNMBF ZCYLV WAPVF QRHZV ZGZEF KBYIO OFXYE VOWGB" +
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"BXVCB XBAWG LQKCM ICRRX MACUO IKHQU AJEGL OIJHH XPVZW JEWBA" +
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"FWAML ZZRXJ EKAHV FASMU LVVUT TGK"
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val freq = doubleArrayOf(
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0.08167, 0.01492, 0.02782, 0.04253, 0.12702, 0.02228, 0.02015,
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0.06094, 0.06966, 0.00153, 0.00772, 0.04025, 0.02406, 0.06749,
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0.07507, 0.01929, 0.00095, 0.05987, 0.06327, 0.09056, 0.02758,
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0.00978, 0.02360, 0.00150, 0.01974, 0.00074
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)
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fun bestMatch(a: DoubleArray): Int {
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val sum = a.sum()
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var bestFit = 1e100
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var bestRotate = 0
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for (rotate in 0..25) {
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var fit = 0.0
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for (i in 0..25) {
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val d = a[(i + rotate) % 26] / sum - freq[i]
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fit += d * d / freq[i]
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}
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if (fit < bestFit) {
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bestFit = fit
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bestRotate = rotate
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}
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}
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return bestRotate
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}
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fun freqEveryNth(msg: IntArray, key: CharArray): Double {
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val len = msg.size
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val interval = key.size
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val out = DoubleArray(26)
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val accu = DoubleArray(26)
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for (j in 0 until interval) {
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out.fill(0.0)
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for (i in j until len step interval) out[msg[i]]++
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val rot = bestMatch(out)
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key[j] = (rot + 65).toChar()
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for (i in 0..25) accu[i] += out[(i + rot) % 26]
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}
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val sum = accu.sum()
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var ret = 0.0
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for (i in 0..25) {
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val d = accu[i] / sum - freq[i]
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ret += d * d / freq[i]
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}
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return ret
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}
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fun decrypt(text: String, key: String): String {
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val sb = StringBuilder()
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var ki = 0
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for (c in text) {
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if (c !in 'A'..'Z') continue
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val ci = (c.toInt() - key[ki].toInt() + 26) % 26
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sb.append((ci + 65).toChar())
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ki = (ki + 1) % key.length
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}
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return sb.toString()
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}
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fun main(args: Array<String>) {
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val enc = encoded.replace(" ", "")
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val txt = IntArray(enc.length) { enc[it] - 'A' }
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var bestFit = 1e100
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var bestKey = ""
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val f = "%f %2d %s"
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println(" Fit Length Key")
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for (j in 1..26) {
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val key = CharArray(j)
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val fit = freqEveryNth(txt, key)
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val sKey = key.joinToString("")
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print(f.format(fit, j, sKey))
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if (fit < bestFit) {
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bestFit = fit
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bestKey = sKey
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print(" <--- best so far")
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}
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println()
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}
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println()
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println("Best key : $bestKey")
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println("\nDecrypted text:\n${decrypt(enc, bestKey)}")
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}
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