114 lines
3.4 KiB
V
114 lines
3.4 KiB
V
import strings
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const 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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const freq = [
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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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fn sum(a []f64) f64 {
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mut s := 0.0
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for f in a {
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s += f
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}
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return s
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}
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fn best_match(a []f64) int {
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s := sum(a)
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mut best_fit, mut best_rotate := 1e100, 0
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for rotate in 0..26 {
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mut fit := 0.0
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for i in 0..26 {
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d := a[(i+rotate)%26]/s - freq[i]
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fit += d * d / freq[i]
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}
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if fit < best_fit {
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best_fit, best_rotate = fit, rotate
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}
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}
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return best_rotate
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}
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fn freq_every_nth(msg []int, mut key []u8) f64 {
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l := msg.len
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interval := key.len
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mut out := []f64{len: 26}
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mut accu := []f64{len: 26}
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for j in 0..interval {
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for z in 0..26 {
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out[z] = 0.0
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}
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for i := j; i < l; i += interval {
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out[msg[i]]++
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}
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rot := best_match(out)
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key[j] = u8(rot + 65)
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for i := 0; i < 26; i++ {
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accu[i] += out[(i+rot)%26]
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}
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}
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s := sum(accu)
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mut ret := 0.0
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for i := 0; i < 26; i++ {
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d := accu[i]/s - 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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fn decrypt(text string, key string) string {
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mut sb := strings.new_builder(128)
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mut ki := 0
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for c in text {
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if c < 'A'[0] || c > 'Z'[0] {
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continue
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}
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ci := (c - key[ki] + 26) % 26
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sb.write_rune(ci + 65)
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ki = (ki + 1) % key.len
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}
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return sb.str()
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}
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fn main() {
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enc := encoded.replace(" ", "")
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mut txt := []int{len: enc.len}
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for i in 0..txt.len {
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txt[i] = int(enc[i] - 'A'[0])
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}
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mut best_fit, mut best_key := 1e100, ""
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println(" Fit Length Key")
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for j := 1; j <= 26; j++ {
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mut key := []u8{len: j}
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fit := freq_every_nth(txt, mut key)
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s_key := key.bytestr()
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print("${fit:.6} ${j:2} $s_key")
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if fit < best_fit {
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best_fit, best_key = fit, s_key
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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("\nBest key : $best_key")
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println("\nDecrypted text:\n${decrypt(enc, best_key)}")
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}
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