src/crypt/decrypter.js

import AESCrypto from './aes-crypto';
import FastAESKey from './fast-aes-key';
import AESDecryptor from './aes-decryptor';

import { ErrorTypes, ErrorDetails } from '../errors';
import { logger } from '../utils/logger';

import Event from '../events';

import { getSelfScope } from '../utils/get-self-scope';

// see https://stackoverflow.com/a/11237259/589493
const global = getSelfScope(); // safeguard for code that might run both on worker and main thread

class Decrypter {
  constructor (observer, config, { removePKCS7Padding = true } = {}) {
    this.logEnabled = true;
    this.observer = observer;
    this.config = config;
    this.removePKCS7Padding = removePKCS7Padding;
    // built in decryptor expects PKCS7 padding
    if (removePKCS7Padding) {
      try {
        const browserCrypto = global.crypto;
        if (browserCrypto) {
          this.subtle = browserCrypto.subtle || browserCrypto.webkitSubtle;
        }
      } catch (e) {}
    }
    this.disableWebCrypto = !this.subtle;
  }

  isSync () {
    return (this.disableWebCrypto && this.config.enableSoftwareAES);
  }

  decrypt (data, key, iv, callback) {
    if (this.disableWebCrypto && this.config.enableSoftwareAES) {
      if (this.logEnabled) {
        logger.log('JS AES decrypt');
        this.logEnabled = false;
      }
      let decryptor = this.decryptor;
      if (!decryptor) {
        this.decryptor = decryptor = new AESDecryptor();
      }

      decryptor.expandKey(key);
      callback(decryptor.decrypt(data, 0, iv, this.removePKCS7Padding));
    } else {
      if (this.logEnabled) {
        logger.log('WebCrypto AES decrypt');
        this.logEnabled = false;
      }
      const subtle = this.subtle;
      if (this.key !== key) {
        this.key = key;
        this.fastAesKey = new FastAESKey(subtle, key);
      }

      this.fastAesKey.expandKey()
        .then((aesKey) => {
          // decrypt using web crypto
          let crypto = new AESCrypto(subtle, iv);
          crypto.decrypt(data, aesKey)
            .catch((err) => {
              this.onWebCryptoError(err, data, key, iv, callback);
            })
            .then((result) => {
              callback(result);
            });
        })
        .catch((err) => {
          this.onWebCryptoError(err, data, key, iv, callback);
        });
    }
  }

  onWebCryptoError (err, data, key, iv, callback) {
    if (this.config.enableSoftwareAES) {
      logger.log('WebCrypto Error, disable WebCrypto API');
      this.disableWebCrypto = true;
      this.logEnabled = true;
      this.decrypt(data, key, iv, callback);
    } else {
      logger.error(`decrypting error : ${err.message}`);
      this.observer.trigger(Event.ERROR, { type: ErrorTypes.MEDIA_ERROR, details: ErrorDetails.FRAG_DECRYPT_ERROR, fatal: true, reason: err.message });
    }
  }

  destroy () {
    let decryptor = this.decryptor;
    if (decryptor) {
      decryptor.destroy();
      this.decryptor = undefined;
    }
  }
}

export default Decrypter;