diff --git a/__tests__/assets/res/abc.res b/__tests__/assets/res/abc.res
new file mode 100644
index 0000000..f117576
Binary files /dev/null and b/__tests__/assets/res/abc.res differ
diff --git a/__tests__/assets/res/magic_number.res b/__tests__/assets/res/magic_number.res
new file mode 100644
index 0000000..113d220
Binary files /dev/null and b/__tests__/assets/res/magic_number.res differ
diff --git a/__tests__/assets/res/too_many_files.res b/__tests__/assets/res/too_many_files.res
new file mode 100644
index 0000000..7c8b46b
Binary files /dev/null and b/__tests__/assets/res/too_many_files.res differ
diff --git a/__tests__/res.int.test.ts b/__tests__/res.int.test.ts
new file mode 100644
index 0000000..08322b9
--- /dev/null
+++ b/__tests__/res.int.test.ts
@@ -0,0 +1,49 @@
+import { readFile } from 'fs-extra';
+
+import { Resource } from '../src';
+
+describe('Res', () => {
+  // This test actually doesn't work with Across.res/Elma.res due to garbage bytes after the end of strings
+  test('toBuffer matches original buffer', async () => {
+    const file = await readFile(`__tests__/assets/res/abc.res`);
+    const res = Resource.from(file);
+    const resBuffer = res.toBuffer();
+    expect(file).toEqual(resBuffer);
+  });
+  test('Parsing matches expected output', async () => {
+    const file = await readFile(`__tests__/assets/res/abc.res`);
+    const res = Resource.from(file);
+    expect(res.files.length).toEqual(3);
+    expect(res.files[0].name).toEqual('a.a');
+    expect(res.files[1].name).toEqual('b.b');
+    expect(res.files[2].name).toEqual('cccccccC.ccc');
+    expect(res.files[0].data).toEqual(Buffer.from('FileA'));
+    expect(res.files[1].data).toEqual(Buffer.from([0, 0, 0]));
+    expect(res.files[2].data).toEqual(Buffer.from('FileC'));
+  });
+  test('toBuffer throws error: Filename too long', async () => {
+    const res = new Resource();
+    res.files.push({ name: 'length=13.bad', data: Buffer.from([0]) });
+    expect(() => res.toBuffer()).toThrowError('Filename length=13.bad is too long (max 12 characters)');
+  });
+  test('toBuffer throws error: Filename no ext', async () => {
+    const res = new Resource();
+    res.files.push({ name: 'noext', data: Buffer.from([0]) });
+    expect(() => res.toBuffer()).toThrowError('Filename noext needs to include a file extension!');
+  });
+  test('toBuffer throws error: Too many files', async () => {
+    const res = new Resource();
+    for (let i = 0; i < 151; i++) {
+      res.files.push({ name: `file{i}.txt`, data: Buffer.from([i]) });
+    }
+    expect(() => res.toBuffer()).toThrowError('Max number of files is 150, but got 151 files');
+  });
+  test('from throws error: Too many files', async () => {
+    const file = await readFile(`__tests__/assets/res/too_many_files.res`);
+    expect(() => Resource.from(file)).toThrowError('Max number of files is 150, but got 151 files');
+  });
+  test('from throws error: Magic number', async () => {
+    const file = await readFile(`__tests__/assets/res/magic_number.res`);
+    expect(() => Resource.from(file)).toThrowError('Magic Number not found, is this really a .res file?');
+  });
+});
diff --git a/package.json b/package.json
index d39d014..d0d310c 100644
--- a/package.json
+++ b/package.json
@@ -57,5 +57,6 @@
   ],
   "dependencies": {
     "buffer": "^6.0.1"
-  }
+  },
+  "packageManager": "yarn@1.22.22+sha512.a6b2f7906b721bba3d67d4aff083df04dad64c399707841b7acf00f6b133b7ac24255f2652fa22ae3534329dc6180534e98d17432037ff6fd140556e2bb3137e"
 }
diff --git a/src/index.ts b/src/index.ts
index 169201a..9fc9f51 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -4,3 +4,4 @@ export * from './shared';
 export * from './util';
 export * from './lgr';
 export * from './state';
+export * from './res';
diff --git a/src/res/Resource.ts b/src/res/Resource.ts
new file mode 100644
index 0000000..49ca83c
--- /dev/null
+++ b/src/res/Resource.ts
@@ -0,0 +1,88 @@
+import { Buffer } from 'buffer';
+
+import { nullpadString, trimString, cryptPiece, CryptKey } from '../util';
+import { BufferInput } from '../shared';
+
+const MAX_FILES = 150;
+const RESOURCE_FILE_SIZE = 24;
+const ENCRYPTED_SIZE = MAX_FILES * RESOURCE_FILE_SIZE;
+const MAGIC_NUMBER = 1347839;
+const HEADER_SIZE = 4 + ENCRYPTED_SIZE + 4;
+const CRYPT_KEY: CryptKey = [23, 9982, 3391, 31];
+
+export interface ResourceFile {
+  name: string;
+  data: Buffer;
+}
+
+export default class Resource {
+  public files: ResourceFile[] = [];
+
+  /**
+   * Loads a resource file from a buffer.
+   * @param buffer
+   */
+  public static from(buffer: BufferInput): Resource {
+    return this.parseBuffer(Buffer.from(buffer));
+  }
+
+  private static parseBuffer(buffer: Buffer): Resource {
+    const res = new Resource();
+
+    const magicNumber = buffer.readUInt32LE(4 + ENCRYPTED_SIZE);
+    if (magicNumber !== MAGIC_NUMBER) throw Error(`Magic Number not found, is this really a .res file?`);
+
+    const fileCount = buffer.readUInt32LE(0);
+    if (fileCount > MAX_FILES) throw Error(`Max number of files is ${MAX_FILES}, but got ${fileCount} files`);
+    const decryptedHeader = this.cryptHeader(buffer.slice(4, 4 + ENCRYPTED_SIZE));
+    for (let i = 0; i < fileCount; i++) {
+      const pos = i * RESOURCE_FILE_SIZE;
+      const name = trimString(decryptedHeader.slice(pos, pos + 16));
+      const length = decryptedHeader.readUInt32LE(pos + 16);
+      const offset = decryptedHeader.readUInt32LE(pos + 20);
+      const data = buffer.slice(offset, offset + length);
+      res.files.push({ name, data });
+    }
+
+    return res;
+  }
+
+  public toBuffer(): Buffer {
+    const fileCount = this.files.length;
+    if (fileCount > MAX_FILES) throw Error(`Max number of files is ${MAX_FILES}, but got ${fileCount} files`);
+
+    const size = HEADER_SIZE + this.files.reduce((sum, file) => sum + file.data.length, 0);
+    const buffer = Buffer.alloc(size);
+    const header = Buffer.alloc(ENCRYPTED_SIZE);
+
+    buffer.writeUInt32LE(fileCount, 0);
+    buffer.writeUInt32LE(MAGIC_NUMBER, 4 + ENCRYPTED_SIZE);
+    let offset = HEADER_SIZE;
+    for (let i = 0; i < fileCount; i++) {
+      const pos = i * RESOURCE_FILE_SIZE;
+      const name = this.files[i].name;
+      const data = this.files[i].data;
+      const length = data.length;
+      if (name.length > 12) throw Error(`Filename ${name} is too long (max 12 characters)`);
+      if (!name.includes('.')) throw Error(`Filename ${name} needs to include a file extension!`);
+      header.write(nullpadString(name, 16), pos, 16, 'ascii');
+      header.writeUInt32LE(length, pos + 16);
+      header.writeUInt32LE(offset, pos + 20);
+      data.copy(buffer, offset);
+      offset += length;
+    }
+
+    const encryptedHeader = Resource.cryptHeader(header);
+    encryptedHeader.copy(buffer, 4);
+
+    return buffer;
+  }
+
+  private static cryptHeader(buffer: Buffer): Buffer {
+    const bufCopy = Buffer.from(buffer);
+    if (bufCopy.length !== ENCRYPTED_SIZE)
+      throw Error(`Invalid resource header length, expected buffer length of ${ENCRYPTED_SIZE}, got ${bufCopy.length}`);
+    const cryptedHeader = cryptPiece(bufCopy, CRYPT_KEY);
+    return cryptedHeader;
+  }
+}
diff --git a/src/res/index.ts b/src/res/index.ts
new file mode 100644
index 0000000..770ac9b
--- /dev/null
+++ b/src/res/index.ts
@@ -0,0 +1 @@
+export { default as Resource } from './Resource';
diff --git a/src/state/State.ts b/src/state/State.ts
index da8671b..93a8ada 100644
--- a/src/state/State.ts
+++ b/src/state/State.ts
@@ -1,7 +1,7 @@
 import { Buffer } from 'buffer';
 
 import { Top10 } from '../shared';
-import { nullpadString, trimString, bufferToTop10, top10ToBuffer } from '../util';
+import { nullpadString, trimString, bufferToTop10, top10ToBuffer, cryptPiece, CryptKey } from '../util';
 
 const STATE_SIZE = 67910;
 const PLAYER_STRUCT_SIZE = 116;
@@ -15,6 +15,7 @@ const NUM_LEVELS = 90;
 const STATE_START = 200;
 const STATE_END = 123432221;
 const STATE_END_ALT = 123432112;
+const CRYPT_KEY: CryptKey = [23, 9782, 3391, 31];
 
 export enum PlayMode {
   Single = 1,
@@ -212,28 +213,13 @@ export default class State {
 
     let curr = 0;
     for (const p of statePieces) {
-      const decryptedPart = this.cryptStatePiece(bufCopy.slice(curr, curr + p));
+      const decryptedPart = cryptPiece(bufCopy.slice(curr, curr + p), CRYPT_KEY);
       decryptedPart.copy(bufCopy, curr);
       curr += p;
     }
     return bufCopy;
   }
 
-  private static cryptStatePiece(buffer: Buffer): Buffer {
-    const bufCopy = Buffer.from(buffer);
-    let ebp8 = 0x17;
-    let ebp10 = 0x2636;
-
-    for (let i = 0; i < buffer.length; i++) {
-      bufCopy[i] ^= ebp8 & 0xff;
-      ebp10 += (ebp8 % 0xd3f) * 0xd3f;
-      ebp8 = ebp10 * 0x1f + 0xd3f;
-      ebp8 = (ebp8 & 0xffff) - 2 * (ebp8 & 0x8000);
-    }
-
-    return bufCopy;
-  }
-
   // State file version; the only supported value is 200.
   public readonly version = STATE_START;
   // Best times lists. state.dat has a fixed-size array of 90 of these.
diff --git a/src/util.ts b/src/util.ts
index 7fa5e86..15129cd 100644
--- a/src/util.ts
+++ b/src/util.ts
@@ -115,3 +115,21 @@ export function bufferToTop10(buffer: BufferInput): Top10 {
     multi,
   };
 }
+
+export type CryptKey = [number, number, number, number];
+export function cryptPiece(buffer: Buffer, key: CryptKey): Buffer {
+  const bufCopy = Buffer.from(buffer);
+  let a = key[0];
+  let b = key[1];
+  const c = key[2];
+  const d = key[3];
+
+  for (let i = 0; i < buffer.length; i++) {
+    bufCopy[i] ^= a & 0xff;
+    b += (a % c) * c;
+    a = b * d + c;
+    a = (a & 0xffff) - 2 * (a & 0x8000);
+  }
+
+  return bufCopy;
+}