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crypto: fix aes crash when tag length too small #38914

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crypto: fix aes crash when tag length too small #38914

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crypto: fix aes crash when tag length too small
XadillaX Jun 3, 2021
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XadillaX Jun 3, 2021
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XadillaX Jun 10, 2021
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XadillaX Jun 10, 2021
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11 changes: 11 additions & 0 deletions lib/internal/crypto/aes.js
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Expand Up @@ -188,6 +188,17 @@ function asyncAesGcmCipher(
const slice = ArrayBufferIsView(data) ?
TypedArrayPrototypeSlice : ArrayBufferPrototypeSlice;
tag = slice(data, -tagByteLength);

// Refs: https://www.w3.org/TR/WebCryptoAPI/#aes-gcm-operations
//
// > If *plaintext* has a length less than *tagLength* bits, then `throw`
// > an `OperationError`.
if (tagByteLength > tag.byteLength) {
throw lazyDOMException(
'The provided data is too small.',
'OperationError');
}

data = slice(data, 0, -tagByteLength);
break;
case kWebCryptoCipherEncrypt:
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29 changes: 29 additions & 0 deletions test/parallel/test-crypto-webcrypto-aes-decrypt-tag-too-small.js
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@@ -0,0 +1,29 @@
'use strict';

const common = require('../common');

if (!common.hasCrypto)
common.skip('missing crypto');

const assert = require('assert');
const crypto = require('crypto').webcrypto;

crypto.subtle.importKey(
'raw',
new Uint8Array(32),
{
name: 'AES-GCM'
},
false,
[ 'encrypt', 'decrypt' ])
.then((k) => {
assert.rejects(async () => {
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This function does not need the async keyword, and using it hides whether the exception is thrown synchronously or the Promise is actually rejected.

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Hmmmmm, Chrome rejects this situation in Promise. So shall we do reject or throw?

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window.crypto.subtle.decrypt({name: 'AES-GCM', iv: new Uint8Array(12)}, k, new Uint8Array(0));
> Promise {<pending>}
Uncaught (in promise) DOMException: The provided data is too small

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I believe that the behavior is correct, and the test works, but it isn't as strict as it could be. assert.rejects is fine, but the async weakens the test:

function fnThatThrows() { throw new Error(); }
async function fnThatRejects() { throw new Error(); }

// With 'async':

assert.rejects(async () => fnThatRejects()); // passes
assert.rejects(async () => fnThatThrows()); // passes, but should not!

// Now remove the 'async' keyword:

assert.rejects(() => fnThatRejects()); // passes
assert.rejects(() => fnThatThrows()); // fails as it should

So I'd simply remove the async keyword from the function declaration :)

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I've resolved it.

return crypto.subtle.decrypt({
name: 'AES-GCM',
iv: new Uint8Array(12),
}, k, new Uint8Array(0));
}, {
name: 'OperationError',
message: /The provided data is too small/,
});
});