feat(AES): add OFB block mode

aes.ts

@@ -1,2 +1,2 @@
-export { AesCbc, AesCfb, AesEcb } from "./src/aes/mod.ts";
+export { AesCbc, AesCfb, AesEcb, AesOfb } from "./src/aes/mod.ts";
 export { Padding } from "./src/utils/padding.ts";

mod.ts

@@ -1,3 +1,3 @@
 export { BlowfishCbc, BlowfishEcb } from "./blowfish.ts";
-export { AesCbc, AesCfb, AesEcb } from "./aes.ts";
+export { AesCbc, AesCfb, AesEcb, AesOfb } from "./aes.ts";
 export { Padding } from "./src/utils/padding.ts";

src/aes/cipher.ts

@@ -157,3 +157,34 @@ export class AesCfb implements BlockCipher {
     return unpad(decrypted, this.padding, AES.BLOCK_SIZE);
   }
 }
+
+export class AesOfb implements BlockCipher {
+  #aes: AES;
+  #prev: Uint8Array;
+
+  constructor(
+    key: Uint8Array,
+    iv: Uint8Array,
+  ) {
+    checkIvSize(iv.length);
+
+    this.#prev = iv.slice();
+    this.#aes = new AES(key);
+  }
+
+  encrypt(data: Uint8Array): Uint8Array {
+    const encrypted = data.slice();
+
+    for (let i = 0; i < data.length; i += AES.BLOCK_SIZE) {
+      this.#aes.encrypt(this.#prev);
+
+      for (let j = 0; j < AES.BLOCK_SIZE; j++) {
+        encrypted[i + j] ^= this.#prev[j];
+      }
+    }
+
+    return encrypted;
+  }
+
+  decrypt = this.encrypt;
+}

src/aes/mod.ts

@@ -1 +1 @@
-export { AesCbc, AesCfb, AesEcb } from "./cipher.ts";
+export { AesCbc, AesCfb, AesEcb, AesOfb } from "./cipher.ts";

tests/aes.test.ts

@@ -1,5 +1,5 @@
 import { assertEquals, assertThrows } from "../dev_deps.ts";
-import { AesCbc, AesCfb, AesEcb } from "../aes.ts";
+import { AesCbc, AesCfb, AesEcb, AesOfb } from "../aes.ts";
 
 // deno-fmt-ignore
 const iv = new Uint8Array([1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16]);
@@ -78,3 +78,19 @@ Deno.test("AES-128-CFB ", () => {
 
   assertEquals(dec, original);
 });
+
+Deno.test("AES-128-OFB ", () => {
+  // deno-fmt-ignore
+  const key = new Uint8Array([1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16]);
+  const iv = new Uint8Array(16);
+
+  const original = new Uint8Array(32);
+
+  const cipher = new AesOfb(key, iv);
+  const decipher = new AesOfb(key, iv);
+
+  const enc = cipher.encrypt(original);
+  const dec = decipher.decrypt(enc);
+
+  assertEquals(dec, original);
+});