crypto_pals/basics.ts

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];
};

type DetectSingleByteXor = (buffs: Buffer[]) => string;
export const detectSingleByteXor: DetectSingleByteXor = (buffs) => {
    const candidates = [] as [number, string][];
    buffs.slice(0, -1).forEach(buff => {
        range(0, 255).forEach(i => {
            const decrypted = decryptSingleByte(buff, i);
            candidates.push([scoreBuffer(decrypted), decrypted.toString('utf-8').trim()]);
        });
    });
    candidates.sort((a, b) => b[0] - a[0]);
    return candidates[0][1];
};