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