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

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+// 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);
+  }
+}