mode-ctr.ts•2.04 kB
// Counter Mode
import { ModeOfOperation } from "./mode.js";
export class CTR extends ModeOfOperation {
// Remaining bytes for the one-time pad
#remaining: Uint8Array;
#remainingIndex: number;
// The current counter
#counter: Uint8Array;
constructor(key: Uint8Array, initialValue?: number | Uint8Array) {
super("CTR", key, CTR);
this.#counter = new Uint8Array(16)
this.#counter.fill(0);
this.#remaining = this.#counter; // This will be discarded immediately
this.#remainingIndex = 16;
if (initialValue == null) { initialValue = 1; }
if (typeof(initialValue) === "number") {
this.setCounterValue(initialValue);
} else {
this.setCounterBytes(initialValue);
}
}
get counter(): Uint8Array { return new Uint8Array(this.#counter); }
setCounterValue(value: number): void {
if (!Number.isInteger(value) || value < 0 || value > Number.MAX_SAFE_INTEGER) {
throw new TypeError("invalid counter initial integer value");
}
for (let index = 15; index >= 0; --index) {
this.#counter[index] = value % 256;
value = Math.floor(value / 256);
}
}
setCounterBytes(value: Uint8Array): void {
if (value.length !== 16) {
throw new TypeError("invalid counter initial Uint8Array value length");
}
this.#counter.set(value);
}
increment() {
for (let i = 15; i >= 0; i--) {
if (this.#counter[i] === 255) {
this.#counter[i] = 0;
} else {
this.#counter[i]++;
break;
}
}
}
encrypt(plaintext: Uint8Array): Uint8Array {
const crypttext = new Uint8Array(plaintext);
for (let i = 0; i < crypttext.length; i++) {
if (this.#remainingIndex === 16) {
this.#remaining = this.aes.encrypt(this.#counter);
this.#remainingIndex = 0;
this.increment();
}
crypttext[i] ^= this.#remaining[this.#remainingIndex++];
}
return crypttext;
}
decrypt(ciphertext: Uint8Array): Uint8Array {
return this.encrypt(ciphertext);
}
}