feat(QMCv2): add map cipher

src/decrypt/qmc_cipher.test.ts

@@ -1,4 +1,5 @@
-import {QmcStaticCipher} from "@/decrypt/qmc_cipher";
+import {QmcMapCipher, QmcStaticCipher} from "@/decrypt/qmc_cipher";
+import fs from 'fs'
 
 test("static cipher [0x7ff8,0x8000) ", () => {
   const expected = new Uint8Array([
@@ -25,3 +26,41 @@ test("static cipher [0,0x10) ", () => {
 
   expect(buf).toStrictEqual(expected)
 })
+
+function loadTestDataMapCipher(name: string): {
+  key: Uint8Array,
+  cipherText: Uint8Array,
+  clearText: Uint8Array
+} {
+  return {
+    key: fs.readFileSync(`testdata/${name}_key.bin`),
+    cipherText: fs.readFileSync(`testdata/${name}_raw.bin`),
+    clearText: fs.readFileSync(`testdata/${name}_target.bin`)
+  }
+}
+
+test("map cipher: get mask", () => {
+  const expected = new Uint8Array([
+    0xBB, 0x7D, 0x80, 0xBE, 0xFF, 0x38, 0x81, 0xFB,
+    0xBB, 0xFF, 0x82, 0x3C, 0xFF, 0xBA, 0x83, 0x79,
+  ])
+  const key = new Uint8Array(256)
+  for (let i = 0; i < 256; i++) key[i] = i
+  const buf = new Uint8Array(16)
+
+  const c = new QmcMapCipher(key)
+  c.decrypt(buf, 0)
+  expect(buf).toStrictEqual(expected)
+})
+
+test("map cipher: real file", async () => {
+  const cases = ["mflac_map", "mgg_map"]
+  for (const name of cases) {
+    const {key, clearText, cipherText} = loadTestDataMapCipher(name)
+    const c = new QmcMapCipher(key)
+
+    c.decrypt(cipherText, 0)
+
+    expect(cipherText).toStrictEqual(clearText)
+  }
+})

src/decrypt/qmc_cipher.ts

@@ -33,11 +33,11 @@ const staticCipherBox = new Uint8Array([
   0xA5, 0x47, 0xF7, 0xF6, 0x00, 0x79, 0x4A, 0x11, //0xF8
 ])
 
-interface streamCipher {
+export interface StreamCipher {
   decrypt(buf: Uint8Array, offset: number): void
 }
 
-export class QmcStaticCipher implements streamCipher {
+export class QmcStaticCipher implements StreamCipher {
 
   public getMask(offset: number) {
     if (offset > 0x7FFF) offset %= 0x7FFF
@@ -51,3 +51,35 @@ export class QmcStaticCipher implements streamCipher {
   }
 }
 
+export class QmcMapCipher implements StreamCipher {
+  key: Uint8Array
+  n: number
+
+  constructor(key: Uint8Array) {
+    if (key.length == 0) throw Error("qmc/cipher_map: invalid key size")
+
+    this.key = key
+    this.n = key.length
+  }
+
+  private static rotate(value: number, bits: number) {
+    let rotate = (bits + 4) % 8;
+    let left = value << rotate;
+    let right = value >> rotate;
+    return (left | right) & 0xff;
+  }
+
+  decrypt(buf: Uint8Array, offset: number): void {
+    for (let i = 0; i < buf.length; i++) {
+      buf[i] ^= this.getMask(offset + i)
+    }
+  }
+
+  private getMask(offset: number) {
+    if (offset > 0x7fff) offset %= 0x7fff;
+
+    const idx = (offset * offset + 71214) % this.n;
+    return QmcMapCipher.rotate(this.key[idx], idx & 0x7)
+  }
+
+}