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system/node_modules/aes-js/src.ts/mode-ofb.ts

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+// Output Feedback
+
+import { ModeOfOperation } from "./mode.js";
+
+export class OFB extends ModeOfOperation {
+  #iv: Uint8Array;
+  #lastPrecipher: Uint8Array;
+  #lastPrecipherIndex: number;
+
+  constructor(key: Uint8Array, iv?: Uint8Array) {
+    super("OFB", key, OFB);
+
+    if (iv) {
+      if (iv.length % 16) {
+        throw new TypeError("invalid iv size (must be 16 bytes)");
+      }
+      this.#iv = new Uint8Array(iv);
+    } else {
+      this.#iv = new Uint8Array(16);
+    }
+
+    this.#lastPrecipher = this.iv;
+    this.#lastPrecipherIndex = 16;
+  }
+
+  get iv(): Uint8Array { return new Uint8Array(this.#iv); }
+
+  encrypt(plaintext: Uint8Array): Uint8Array {
+    if (plaintext.length % 16) {
+      throw new TypeError("invalid plaintext size (must be multiple of 16 bytes)");
+    }
+
+    const ciphertext = new Uint8Array(plaintext);
+    for (let i = 0; i < ciphertext.length; i++) {
+      if (this.#lastPrecipherIndex === 16) {
+          this.#lastPrecipher = this.aes.encrypt(this.#lastPrecipher);
+          this.#lastPrecipherIndex = 0;
+      }
+      ciphertext[i] ^= this.#lastPrecipher[this.#lastPrecipherIndex++];
+    }
+
+    return ciphertext;
+  }
+
+  decrypt(ciphertext: Uint8Array): Uint8Array {
+    if (ciphertext.length % 16) {
+        throw new TypeError("invalid ciphertext size (must be multiple of 16 bytes)");
+    }
+    return this.encrypt(ciphertext);
+  }
+}