Web Crypto API throws `DOMException` on AES decryption

Question

I want to perform basic AES-CBC decryption. I have the string encData that is encrypted with the 128-bits key rawKey, the initialization vector defaultIV is zero. I want to use only Web Crypto API, without 3th-party libraries. Is it possible to do?

window.crypto.subtle.decrypt of Web Crypto API throws the exception when I use it: DOMException (and no more information) in Chromium and OperationError: The operation failed for an operation-specific reason in Firefox.

What is it the problem?

The key and encrypted data is OK, I have checked it in an online decryption (use the hex string from the console output).

The code:

!async function script() {

// ArrayBuffer to Hex String. https://stackoverflow.com/a/40031979/11468937
function buf2hex(buffer) {
    return Array.prototype.map.call(new Uint8Array(buffer), x => ('00' + x.toString(16)).slice(-2)).join('');
}


const defaultIV = new Uint8Array(16);
const rawKey    = new Uint8Array([42, 40, 254, 9, 99, 201, 174, 52, 226, 21, 90, 155, 81, 50, 2, 9]);
const encData   = new Uint8Array([102, 80, 220, 73, 185, 233, 85, 7, 195, 196, 137, 107, 65, 150, 162, 161, 80, 82, 26, 18, 110, 247, 189, 176, 35, 197, 140, 4, 138, 75, 159, 197, 75, 88, 131, 23, 235, 125, 96, 81, 41, 170, 220, 45, 64, 55, 30, 68, 39, 6, 112, 194, 243, 209, 177, 173, 54, 71, 21, 172, 62, 147, 112, 76]);

console.log("defaultIV\n", defaultIV, buf2hex(defaultIV));
console.log("rawKey\n",    rawKey,    buf2hex(rawKey));
console.log("encData\n",   encData,   buf2hex(encData));


const key = await crypto.subtle.importKey(
    "raw",
    rawKey,
    "AES-CBC",
    true,
    ["decrypt"]
);
console.log("key", key);


// It throws "Uncaught (in promise) DOMException"
const decrypted  = await crypto.subtle.decrypt(
    {
        name: "AES-CBC",
        iv: defaultIV
    },
    key,
    encData
);
console.log("decrypted", decrypted);

}();

The expected output is: `MEGA{"n":"SharedFile.jpg","c":"GRSM8+c1HUmlmyDuTJVrDwSDpqRV"} ` I have used aes.online-domain-tools.com — KeyKi, Feb 08 '20 at 00:14
DOM Exception is the document object model. It's your browser complaining about your client side code. I'll look into that library. — Sydney Y, Feb 08 '20 at 00:51
In Firefox I get `OperationError: The operation failed for an operation-specific reason`. — KeyKi, Feb 08 '20 at 00:56
I'm at a loss right now. Can you tell me what it is you are trying to do? I'm pretty confident in JavaScript so I think I can help, but I'm not familiar with cryptography. Example: "I have a JSON string encrypted and hashed that I am trying to decode" — Sydney Y, Feb 08 '20 at 01:57
A basic AES-CBC decryption. I have a string `encData` that is encrypted with a 128-bits key `rawKey`, an initialization vector `defaultIV` is zero. I wanted to use `Web Crypto API`, without 3th-party libraries. — KeyKi, Feb 08 '20 at 02:11

score 7 · Accepted Answer · answered Feb 10 '20 at 03:15

A padding (PKCS #7). It was the problem. My encrypted text that I get from a 3th-party service has no padding (that adds before encryption).

Web Crypto API does not work with data encrypted without the padding.

AES-JS has easy to use API, but it works only with a text without the padding (In my case it's OK), but if you use it to decrypt a cipher text with the padding you need to manually remove it from the result string.

CryptoJS API looks ancient, but it works fine in both case, when the text has the padding or not.

You need to transform ArrayBuffer to something other:

let key       = ab_to_hex(keyArrayBuffer);
let iv        = ab_to_bin_str(ivArrayBuffer);
let encrypted = ab_to_bin_str(encryptedArrayBuffer);

function decrypt(key, iv, encrypted) {
    const plaintextArray = CryptoJS.AES.decrypt(
        { ciphertext: CryptoJS.enc.Latin1.parse(encrypted) },
        CryptoJS.enc.Hex.parse(key),
        { iv: CryptoJS.enc.Latin1.parse(iv) }
    );
    return CryptoJS.enc.Utf8.stringify(plaintextArray);
}

function ab_to_hex(buffer) {
    return Array.from(new Uint8Array(buffer)).map(n => ("0" + n.toString(16)).slice(-2)).join("");
}

function ab_to_bin_str(buffer) {
    return String.fromCharCode(...new Uint8Array(buffer));
}

It's not important, but I should note that my string has a padding, but it is ZeroPadding. I did not see the tailing zeros in console, but they affected on the string length. CryptoJS automatically removes the Pkcs7 padding (if it exists) by default, but not other types. So you may specify the padding type in the third parameter (where `iv`), for example, – `padding: CryptoJS.pad.ZeroPadding`. — KeyKi, Feb 10 '20 at 23:14

score 0 · Answer 2 · answered Feb 09 '20 at 23:45

See this post, better to use AES-GCM if possible: Webcrypto AES-CBC Decrypt: Operation Error - The operation failed for an operation-specific reason

You can test your browser version for what it supports using this test suite - https://peculiarventures.github.io/pv-webcrypto-tests/

It is certainly possible to do AES-CBC with WebCrypto: https://github.com/diafygi/webcrypto-examples#aes-cbc

Web Crypto API throws `DOMException` on AES decryption

2 Answers2

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