// 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);
}
}