Data commit

Task/Vigen-re-cipher-Cryptanalysis/Rust/vigen-re-cipher-cryptanalysis.rust

@@ -0,0 +1,109 @@
+use std::iter::FromIterator;
+
+const CRYPTOGRAM: &str = "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";
+
+const FREQUENCIES: [f32; 26] = [
+    0.08167, 0.01492, 0.02202, 0.04253, 0.12702, 0.02228, 0.02015, 0.06094, 0.06966, 0.00153,
+    0.01292, 0.04025, 0.02406, 0.06749, 0.07507, 0.01929, 0.00095, 0.05987, 0.06327, 0.09356,
+    0.02758, 0.00978, 0.02560, 0.00150, 0.01994, 0.00077,
+];
+
+fn best_match(a: &[f32]) -> u8 {
+    let sum: f32 = a.iter().sum();
+    let mut best_fit = std::f32::MAX;
+    let mut best_rotate = 0;
+    for rotate in 0..=25 {
+        let mut fit = 0.;
+        for i in 0..=25 {
+            let char_freq = FREQUENCIES[i];
+            let idx = (i + rotate as usize) % 26 as usize;
+            let d = a[idx] / sum - char_freq;
+            fit += d * d / char_freq;
+        }
+        if fit < best_fit {
+            best_fit = fit;
+            best_rotate = rotate;
+        }
+    }
+
+    best_rotate
+}
+
+fn freq_every_nth(msg: &[u8], key: &mut [char]) -> f32 {
+    let len = msg.len();
+    let interval = key.len();
+    let mut accu = [0.; 26];
+    for j in 0..interval {
+        let mut out = [0.; 26];
+        for i in (j..len).step_by(interval) {
+            let idx = msg[i] as usize;
+            out[idx] += 1.;
+        }
+        let rot = best_match(&out);
+        key[j] = char::from(rot + b'A');
+        for i in 0..=25 {
+            let idx: usize = (i + rot as usize) % 26;
+            accu[i] += out[idx];
+        }
+    }
+    let sum: f32 = accu.iter().sum();
+    let mut ret = 0.;
+    for i in 0..=25 {
+        let char_freq = FREQUENCIES[i];
+        let d = accu[i] / sum - char_freq;
+        ret += d * d / char_freq;
+    }
+    ret
+}
+
+fn decrypt(text: &str, key: &str) -> String {
+    let key_chars_cycle = key.as_bytes().iter().map(|b| *b as i32).cycle();
+    let is_ascii_uppercase = |c: &u8| (b'A'..=b'Z').contains(c);
+    text.as_bytes()
+        .iter()
+        .filter(|c| is_ascii_uppercase(c))
+        .map(|b| *b as i32)
+        .zip(key_chars_cycle)
+        .fold(String::new(), |mut acc, (c, key_char)| {
+            let ci: u8 = ((c - key_char + 26) % 26) as u8;
+            acc.push(char::from(b'A' + ci));
+            acc
+        })
+}
+fn main() {
+    let enc = CRYPTOGRAM
+        .split_ascii_whitespace()
+        .collect::<Vec<_>>()
+        .join("");
+    let cryptogram: Vec<u8> = enc.as_bytes().iter().map(|b| u8::from(b - b'A')).collect();
+    let mut best_fit = std::f32::MAX;
+    let mut best_key = String::new();
+    for j in 1..=26 {
+        let mut key = vec!['\0'; j];
+        let fit = freq_every_nth(&cryptogram, &mut key);
+        let s_key = String::from_iter(key); // 'from_iter' is imported from std::iter::FromIterator;
+        if fit < best_fit {
+            best_fit = fit;
+            best_key = s_key;
+        }
+    }
+
+    println!("best key: {}", &best_key);
+    println!("\nDecrypted text:\n{}", decrypt(&enc, &best_key));
+}