♻ Extract updateKeys into separate file

src/ssn/decryption/decryptFile.ts

@@ -1,16 +1,16 @@
-import getCrc from './getCrc';
-import int32Mul from './int32Mul';
+import updateKeys from './updateKeys';
 
 export default function decryptFile(dv: DataView, length: number, [key0, key1, key2]: [number, number, number]) {
-  for (let j = 0; j < length; j += 1) {
-      let testChar = dv.getUint8(j);
+  for (let i = 0; i < length; i += 1) {
+    //read and decrypt byte
+    let curChar = dv.getUint8(i);
     const keyPart = (key2 | 2) & 0xFFFF;
     const decryptedByte = (keyPart * (keyPart ^ 1)) >>> 8;
-      testChar ^= decryptedByte & 0xFF;
-      key0 = getCrc(key0, testChar);
-      key1 = ((int32Mul(((key1 + (key0 & 0xFF)) >>> 0), 134775813) >>> 0) + 1) >>> 0;
-      key2 = getCrc(key2, key1 >>> 24);
-      dv.setUint8(j, testChar);
+    curChar ^= decryptedByte & 0xFF;
+    dv.setUint8(i, curChar);
+
+    //update keys
+    [key0, key1, key2] = updateKeys([key0, key1, key2], curChar);
   }
   //if it was decrypted, we skip the first 12 bytes (random encryption header)
   return new DataView(dv.buffer, 12);

src/ssn/decryption/getDecryptionKeys.ts

@@ -1,22 +1,19 @@
-import getCrc from './getCrc';
-import int32Mul from './int32Mul';
+import updateKeys from './updateKeys';
 
-export default function getDecryptionKeys(password: Uint8Array) {
-  const keys: [number, number, number] = [0x12345678, 0x23456789, 0x34567890];
+export default function getDecryptionKeys(password: Uint8Array): [number, number, number] {
+  let [key0, key1, key2] = [0x12345678, 0x23456789, 0x34567890];
   const passwordLength = password.length;
 
-  //update keys
+  //read through password
   for (let i = 0; i < passwordLength; i++) {
-    if (password[i] === 0) { break; }
-    keys[0] = getCrc(keys[0], password[i]);
-    keys[1] =
-        ((
-            int32Mul((
-                ((keys[1] >>> 0) + (keys[0] & 0xFF)) >>> 0
-            ), 134775813) >>> 0
-        ) + 1) >>> 0;
-    keys[2] = getCrc(keys[2] >>> 0, keys[1] >>> 24);
+    const curChar = password[i];
+
+    //Exit early if there's a zero byte in the password
+    if (curChar === 0) { break; }
+
+    //update keys
+    [key0, key1, key2] = updateKeys([key0, key1, key2], curChar);
   }
 
-  return keys;
+  return [key0, key1, key2];
 }

src/ssn/decryption/updateKeys.ts

@@ -0,0 +1,10 @@
+import getCrc from './getCrc';
+import int32Mul from './int32Mul';
+
+export default function updateKeys([key0, key1, key2]: [number, number, number], curChar: number): [number, number, number] {
+  key0 = getCrc(key0, curChar);
+  key1 = ((int32Mul(((key1 + (key0 & 0xFF)) >>> 0), 134775813) >>> 0) + 1) >>> 0;
+  key2 = getCrc(key2, key1 >>> 24);
+
+  return [key0, key1, key2];
+}