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

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+// Cipher Feedback
+
+import { ModeOfOperation } from "./mode.js";
+
+export class CFB extends ModeOfOperation {
+  #iv: Uint8Array;
+  #shiftRegister: Uint8Array;
+
+  readonly segmentSize!: number;
+
+  constructor(key: Uint8Array, iv?: Uint8Array, segmentSize: number = 8) {
+    super("CFB", key, CFB);
+
+    // This library currently only handles byte-aligned segmentSize
+    if (!Number.isInteger(segmentSize) || (segmentSize % 8)) {
+      throw new TypeError("invalid segmentSize");
+    }
+
+    Object.defineProperties(this, {
+      segmentSize: { enumerable: true, value: segmentSize }
+    });
+
+    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.#shiftRegister = this.iv;
+  }
+
+  get iv(): Uint8Array { return new Uint8Array(this.#iv); }
+
+  #shift(data: Uint8Array): void {
+    const segmentSize = this.segmentSize / 8;
+
+    // Shift the register
+    this.#shiftRegister.set(this.#shiftRegister.subarray(segmentSize));
+    this.#shiftRegister.set(data.subarray(0, segmentSize), 16 - segmentSize);
+  }
+
+  encrypt(plaintext: Uint8Array): Uint8Array {
+    if (8 * plaintext.length % this.segmentSize) {
+      throw new TypeError("invalid plaintext size (must be multiple of segmentSize bytes)");
+    }
+
+    const segmentSize = this.segmentSize / 8;
+
+    const ciphertext = new Uint8Array(plaintext);
+
+    for (let i = 0; i < ciphertext.length; i += segmentSize) {
+      const xorSegment = this.aes.encrypt(this.#shiftRegister);
+      for (let j = 0; j < segmentSize; j++) {
+        ciphertext[i + j] ^= xorSegment[j];
+      }
+
+      this.#shift(ciphertext.subarray(i));
+    }
+
+    return ciphertext;
+  }
+
+  decrypt(ciphertext: Uint8Array): Uint8Array {
+    if (8 * ciphertext.length % this.segmentSize) {
+        throw new TypeError("invalid ciphertext size (must be multiple of segmentSize bytes)");
+    }
+
+    const segmentSize = this.segmentSize / 8;
+
+    const plaintext = new Uint8Array(ciphertext);
+
+    for (let i = 0; i < plaintext.length; i += segmentSize) {
+      const xorSegment = this.aes.encrypt(this.#shiftRegister);
+      for (let j = 0; j < segmentSize; j++) {
+        plaintext[i + j] ^= xorSegment[j];
+      }
+
+      this.#shift(ciphertext.subarray(i));
+    }
+
+    return plaintext;
+  }
+}