hls.js/src/crypt/aes-crypto.ts

JavaScript HLS client using MediaSourceExtension

import { DecrypterAesMode } from './decrypter-aes-mode';

export default class AESCrypto {
  private subtle: SubtleCrypto;
  private aesIV: Uint8Array;
  private aesMode: DecrypterAesMode;

  constructor(subtle: SubtleCrypto, iv: Uint8Array, aesMode: DecrypterAesMode) {
    this.subtle = subtle;
    this.aesIV = iv;
    this.aesMode = aesMode;
  }

  decrypt(data: ArrayBuffer, key: CryptoKey) {
    switch (this.aesMode) {
      case DecrypterAesMode.cbc:
        return this.subtle.decrypt(
          { name: 'AES-CBC', iv: this.aesIV },
          key,
          data,
        );
      case DecrypterAesMode.ctr:
        return this.subtle.decrypt(
          { name: 'AES-CTR', counter: this.aesIV, length: 64 }, //64 : NIST SP800-38A standard suggests that the counter should occupy half of the counter block
          key,
          data,
        );
      default:
        throw new Error(`[AESCrypto] invalid aes mode ${this.aesMode}`);
    }
  }
}