Initial commit

basics.ts

@@ -0,0 +1,92 @@
+import { range, englishFreqs } from './utils';
+
+type HexToBuff = (hex: string) => Buffer;
+export const hexToBuff: HexToBuff = (hex) => Buffer.from(hex, 'hex');
+
+type BuffTo64 = (buff: Buffer) => string;
+export const buffTo64: BuffTo64 = (buff) => buff.toString('base64');
+
+type XorBuffers = (buff1: Buffer, buff2: Buffer) => Buffer;
+export const xorBuffers: XorBuffers = (buff1, buff2) => {
+    const resBuff = Buffer.alloc(buff1.length);
+    range(0, buff1.length).forEach(i => {
+        resBuff[i] = buff1[i] ^ buff2[i];
+    });
+    return resBuff;
+};
+
+type EncryptSingleByte = (msg: Buffer, key: number) => Buffer;
+export const encryptSingleByte: EncryptSingleByte = (msg, key) => {
+    const resBuffer = Buffer.alloc(msg.length);
+    range(0, msg.length).forEach(i => {
+        resBuffer[i] = msg[i] ^ key;
+    });
+    return resBuffer;
+};
+
+type DecryptSingleByte = (msg: Buffer, key: number) => Buffer;
+export const decryptSingleByte: DecryptSingleByte = (msg, key) => {
+    const resBuffer = Buffer.alloc(msg.length);
+    range(0, msg.length).forEach(i => {
+        resBuffer[i] = msg[i] ^ key;
+    });
+    return resBuffer;
+};
+
+type EnglishByteFreqs = () => { [id: number]: number };
+const englishByteFreqs: EnglishByteFreqs = () => {
+    const byteFreqs = {} as { [id: number]: number };
+    range(0, 255).forEach(i => byteFreqs[i] = 0);
+
+    Object.keys(englishFreqs).forEach(k => byteFreqs[k] = englishFreqs[k]);
+
+    return byteFreqs;
+};
+
+type ByteFreqs = (buff: Buffer) => { [id: number]: number };
+const byteFreqs: ByteFreqs = (buff) => {
+    const freqs = {} as { [id: number]: number };
+    let n = 0;
+    range(0, 255).forEach(i => freqs[i] = 0);
+
+    buff.forEach(b => {
+        freqs[b]++;
+        n++;
+    });
+
+    Object.keys(freqs).forEach(b => freqs[b] = freqs[b] / n);
+
+    return freqs;
+};
+
+type ScoreBuffer = (buff: Buffer) => number;
+export const scoreBuffer: ScoreBuffer = (buff) => {
+    const msgLower = Buffer.from(buff.toString('utf-8').toLowerCase(), 'utf-8');
+    const engBFreqs = englishByteFreqs();
+
+    const msgFreq = byteFreqs(msgLower);
+
+    let [cosSimilarity, normMsgFreq, normEngFreq] = [0, 0, 0];
+
+    range(0, 255).forEach(i => {
+        cosSimilarity += msgFreq[i] * engBFreqs[i];
+        normMsgFreq += msgFreq[i] ** 2;
+        normEngFreq += engBFreqs[i] ** 2;
+    });
+    normMsgFreq = Math.sqrt(normMsgFreq);
+    normEngFreq = Math.sqrt(normEngFreq);
+    cosSimilarity /= normMsgFreq * normEngFreq;
+
+    return cosSimilarity;
+};
+
+type CrackSingleByteKeyMsg = (msg: string) => string;
+export const crackSingleByteKeyMsg: CrackSingleByteKeyMsg = (msg) => {
+    const candidates = [] as [number, string][];
+    range(0, 255).forEach(i => {
+        const decrypted = decryptSingleByte(Buffer.from(msg, 'hex'), i);
+        candidates.push([scoreBuffer(decrypted), decrypted.toString('utf-8')]);
+    });
+    candidates.sort((a, b) => b[0] - a[0]);
+    return candidates[0][1];
+};