How to decrypt AES with Google Apps Script

Question

I am trying to decrypt AES with GAS. The target of decryption is a document file retrieved by Amazon Selling Partner API.
The key, iv, and URL are obtained by the API, and I want to decrypt the data downloaded by accessing the URL with the key and iv.
However, the decrypted text is either empty or garbled.
Can you please tell me what is wrong with the following code? The code uses cCryptoGS, which is a wrapper library for CryptoJS.

const decrypt_test = () => {
  const url = 'https://tortuga-prod-fe.s3-us-west-2.amazonaws.com/%2FNinetyDays/amzn1.tortuga.3.5d4685fe-cdf1-4f37-8dfc-a25b85468e34.T1J5QXLEXAMPLE';

  const response = UrlFetchApp.fetch(url);
  const file = response.getContentText();

  const key = 'xiZ8FGT6pYo49ZwfvAplJxKgO0qW46Morzs5aEXAMPLE';
  const iv = 'aoGh0rhbB3ALlCFKiEXAMPLE';
  const enc_key = cCryptoGS.CryptoJS.enc.Base64.parse(key);
  const enc_iv = cCryptoGS.CryptoJS.enc.Base64.parse(iv);
  const cipherParams = cCryptoGS.CryptoJS.lib.CipherParams.create({
      ciphertext: file//cCryptoGS.CryptoJS.enc.Base64.parse(file)
  });

  console.log(`enc_key_length:${enc_key.words.length}`);
  console.log(`enc_iv_length:${enc_iv.words.length}`);

  const decryptedMessage = cCryptoGS.CryptoJS.AES.decrypt(cipherParams, enc_key, { iv: enc_iv, mode: cCryptoGS.CryptoJS.mode.CBC}).toString();

  console.log(`decryptedMessage:${decryptedMessage}`);

  return decryptedMessage;
};

[output]

2021/06/20 20:04:04 debug   enc_key_length:8
2021/06/20 20:04:04 debug   enc_iv_length:4
2021/06/20 20:04:04 debug   decryptedMessage:bfc095f3ecec221e8585ceb68031078d25112f5f26ea2c1f80470f5f4f19f2e1c2cd94638e8666c3486fa29191b568bcd9e8d5a3bdcbbc05456f0567bb6cdae675fa044f94e560379d16b1d370cd7c4a9c5afbbcf4fde2694ed01c1b7950eaabc65e46c4640d8f0814bfe66e8ae65f7768136ac4615624be25373d665ee8fde82742e26664d7c09c61ac8994dc3052f0f22d5042f0b407d696e3c84a3906350dc60c46001ef7865d0c6594c57c5af22616688e028f52d4f12b538d0580c420fdcb0ee61287d4ee2629cd7d39f739d63e84dd75e948eaffb4383076f0c66997

I referred to these answers for decryption in CryptoJS and decryption of the SP API documentation [How to decrypt AES with CryptoJS](https://stackoverflow.com/a/66815024) [Decrypting Amazon SP API Report Document using python](https://stackoverflow.com/a/66865573) — thimone, Jun 20 '21 at 11:56

score 0 · Accepted Answer · answered Jul 11 '21 at 02:30

The following code solved the problem

const decrypt_test = () => {
  const url = 'https://tortuga-prod-fe.s3-us-west-2.amazonaws.com/%2FNinetyDays/EXAMPLE';

  let options = {
    'method': 'get',
    'muteHttpExceptions': true,
  };

  const response = UrlFetchApp.fetch(url, options);
  
  const file = response.getBlob().getBytes();

  const key = 'xiZ8FGT6pYo49ZwfvAplJxKgO0qW46MoEXAMPLE';
  const iv = 'aoGh0rhbB3ALlCFKiuJEXAMPLE';
  const enc_key = cCryptoGS.CryptoJS.enc.Base64.parse(key);
  const enc_iv = cCryptoGS.CryptoJS.enc.Base64.parse(iv);
  const cipherParams = cCryptoGS.CryptoJS.lib.CipherParams.create({
      ciphertext: cCryptoGS.CryptoJS.enc.Hex.parse(hexes(file))
  });

  const decryptedMessage = cCryptoGS.CryptoJS.AES.decrypt(cipherParams, enc_key,
                           { iv: enc_iv, mode: cCryptoGS.CryptoJS.mode.CBC}).toString();

  console.log(`decryptedMessage:${decryptedMessage}`);

  const bin = bytes(decryptedMessage)
  const myBlob = Utilities.newBlob(bin, MimeType.TEXT, "decrypted.csv");
  DriveApp.createFile(myBlob);
};

const bytes = (hexstr) => {
  ary = [];
    for (var i = 0; i < hexstr.length; i += 2) {
      ary.push(parseInt(hexstr.substr(i, 2), 16));
  }
  return ary;
}

const hexes = (ary) => {
  return ary.map((e) => ( '00' + (e < 0 ? e += 0x0100 : e).toString(16)).slice(-2)).join('')
}

How to decrypt AES with Google Apps Script

1 Answers1