Miasma_Archive/tests/scramble/stringtool.test.ts

import { describe, expect, test } from "bun:test";

import { StringScrambler } from "../../src/utils/stringtool";

describe("StringScrambler", () => {
  const PASSPHRASE = "ctf-test-passphrase";
  const SALT = "test-salt-value";

  describe("round-trip with same instance", () => {
    const scrambler = new StringScrambler(PASSPHRASE, SALT);

    test.each([
      ["empty string", ""],
      ["single char", "x"],
      ["two chars", "AB"],
      ["short ascii", "hello"],
      ["ascii with punctuation", "Hello, World!"],
      ["mixed symbols", "longer string with numbers 123 and symbols !@#"],
      ["whitespace only", "   \t  "],
      ["control chars", "line1\nline2\tend"],
      ["unicode latin", "café résumé"],
      ["unicode emoji", "rocket 🚀 and 👍🏽"],
      ["cjk", "中文字符串"],
      ["long string", "The quick brown fox jumps over the lazy dog. ".repeat(20)],
      ["binary-like bytes", String.fromCharCode(...Array.from({ length: 256 }, (_, i) => i))],
    ])("should round-trip %s", (_label, value) => {
      const encoded = scrambler.encode(value);
      const decoded = scrambler.decode(encoded);
      expect(decoded).toBe(value);
    });
  });

  describe("round-trip across separate instances with same passphrase+ salt", () => {
    test("should decode with a different instance using the same parameters", () => {
      const a = new StringScrambler(PASSPHRASE, SALT);
      const b = new StringScrambler(PASSPHRASE, SALT);
      const value = "cross-instance secret payload";
      expect(b.decode(a.encode(value))).toBe(value);
    });

    test("should round-trip multiple values across instances", () => {
      const a = new StringScrambler(PASSPHRASE, SALT);
      const b = new StringScrambler(PASSPHRASE, SALT);
      for (const value of ["one", "two", "three 🎉", "中文"]) {
        expect(b.decode(a.encode(value))).toBe(value);
      }
    });
  });

  describe("encoding properties", () => {
    const scrambler = new StringScrambler(PASSPHRASE, SALT);

    test("should produce a valid base64 string", () => {
      expect(scrambler.encode("hello world")).toMatch(
        /^[A-Za-z0-9+/]+=*$/,
      );
    });

    test("should produce different ciphertext for the same plaintext", () => {
      const value = "same plaintext";
      const e1 = scrambler.encode(value);
      const e2 = scrambler.encode(value);
      expect(e1).not.toBe(e2);
      expect(scrambler.decode(e1)).toBe(value);
      expect(scrambler.decode(e2)).toBe(value);
    });

    test("should have a 16-byte encrypted nonce prefix", () => {
      const value = "abcdef";
      const encoded = scrambler.encode(value);
      const buf = Buffer.from(encoded, "base64");
      expect(buf.length).toBe(16 + Buffer.byteLength(value, "utf8"));
    });

    test("nonce should differ between encodings", () => {
      const b1 = Buffer.from(scrambler.encode("a"), "base64").subarray(0, 16);
      const b2 = Buffer.from(scrambler.encode("a"), "base64").subarray(0, 16);
      expect(b1.equals(b2)).toBe(false);
    });

    test("nonce bytes should be non-zero and not the raw nonce", () => {
      const encoded = scrambler.encode("test");
      const nonceBytes = Buffer.from(encoded, "base64").subarray(0, 16);
      // Encrypted nonce should not be trivially identifiable
      const allZero = nonceBytes.every((b) => b === 0);
      expect(allZero).toBe(false);
    });
  });

  describe("CBC diffusion", () => {
    const scrambler = new StringScrambler(PASSPHRASE, SALT);

    test("changing one byte of plaintext changes subsequent ciphertext bytes", () => {
      const a = Buffer.from(scrambler.encode("A".repeat(16)), "base64").subarray(16);
      const b = Buffer.from(scrambler.encode("B" + "A".repeat(15)), "base64").subarray(16);
      // With CBC chaining, the first byte differs AND subsequent bytes propagate
      let diffCount = 0;
      for (let i = 0; i < a.length; i++) {
        if (a[i] !== b[i]) diffCount++;
      }
      expect(diffCount).toBeGreaterThan(1);
    });

    test("changing one byte mid-string changes all subsequent bytes", () => {
      const prefix = "AAAA";
      const a = Buffer.from(
        scrambler.encode(prefix + "AAAA"),
        "base64",
      ).subarray(16);
      const b = Buffer.from(
        scrambler.encode(prefix + "BBBB"),
        "base64",
      ).subarray(16);
      let diffCount = 0;
      for (let i = 0; i < a.length; i++) {
        if (a[i] !== b[i]) diffCount++;
      }
      expect(diffCount).toBeGreaterThan(1);
    });
  });

  describe("multi-round", () => {
    const scrambler = new StringScrambler(PASSPHRASE, SALT);

    test("three rounds still round-trip correctly", () => {
      const value = "multi-round verification string";
      expect(scrambler.decode(scrambler.encode(value))).toBe(value);
    });

    test("ciphertext size equals plaintext size plus nonce", () => {
      for (const value of ["", "a", "hello world", "x".repeat(1000)]) {
        const encoded = scrambler.encode(value);
        const buf = Buffer.from(encoded, "base64");
        expect(buf.length).toBe(16 + Buffer.byteLength(value, "utf8"));
      }
    });
  });

  describe("isolation between parameters", () => {
    test("should NOT decode correctly with a different passphrase", () => {
      const a = new StringScrambler("pass-one", SALT);
      const b = new StringScrambler("pass-two", SALT);
      const encoded = a.encode("top secret");
      expect(b.decode(encoded)).not.toBe("top secret");
    });

    test("should NOT decode correctly with a different salt", () => {
      const a = new StringScrambler(PASSPHRASE, "salt-one");
      const b = new StringScrambler(PASSPHRASE, "salt-two");
      const encoded = a.encode("top secret");
      expect(b.decode(encoded)).not.toBe("top secret");
    });

    test("different salts produce completely different ciphertexts", () => {
      const a = new StringScrambler(PASSPHRASE, "salt-A");
      const b = new StringScrambler(PASSPHRASE, "salt-B");
      const e1 = a.encode("same input");
      const e2 = b.encode("same input");
      expect(e1).not.toBe(e2);
    });
  });

  describe("default (random) parameters", () => {
    test("should round-trip within a single instance", () => {
      const scrambler = new StringScrambler();
      const value = "self-contained secret";
      expect(scrambler.decode(scrambler.encode(value))).toBe(value);
    });

    test("should not be decodable by a fresh default instance", () => {
      const a = new StringScrambler();
      const b = new StringScrambler();
      expect(b.decode(a.encode("hello"))).not.toBe("hello");
    });

    test("default salt and explicit salt produce different encodings", () => {
      const a = new StringScrambler(PASSPHRASE);
      const b = new StringScrambler(PASSPHRASE, SALT);
      expect(a.encode("test")).not.toBe(b.encode("test"));
    });
  });
});