AES-GCM decrypt taglength

[pierresegonne]

Hi! Incredible work!

If the taglength is not provided in the algorithm parameter of the crypto.subtle.decrypt() method it won't be correctly set to 128, and thus the decrypt will throw an error

[EternalDeiwos]

Hi, would you be referring to this logic?

https://github.com/anvilresearch/webcrypto/blob/master/src/algorithms/AES-GCM.js#L139-L143

I'm pretty sure that should result in the tagLength defaulting to 128.

[thelunararmy]

Not getting this error, can you test again and verify.

[christiansmith]

@pierresegonne thanks for the kind words and for filing the issue. Since we're not able to reproduce the error, could you please provide a few additional details about your OS, node versions, etc? And perhaps the snippet of code that's throwing? Thanks again!

[pierresegonne]

here is my decrypt function:

`async function decrypt(encrypted) {

let content = contentDecoder(encrypted);
// password handling
// encoding
let pwUtf8 = encoder.encode(password);
// hashing
let hash = cryptoN.createHash('sha256');
hash.update(pwUtf8);
let pwHash = hash.digest();

// IV
let iv = content.iv;

// ALG
let alg = {name: algorithm, iv: iv, tagLength : 128};

// KEY GENERATION
let cryptoKey = await crypto.subtle.importKey('raw', pwHash, alg, false, ['encrypt', 'decrypt']);

// Decrypt
let data = content.contentBuffer;
let decrypted = await crypto.subtle.decrypt(alg, cryptoKey, data);

// display
console.log(decoder.decode(decrypted));

}`

If I don't precise the tagLength in the alg variable, I catch the following error : Error: Data length cannot be less than tagLength.

I went into the webcrypto/AES-GCM.js file and displayed algorithm.tagLength right before

2. Verify data length and got that algorithm.tagLength is undefined

So the way I see it,

the 2. Verify data length should become : if ((data.length*8)<tagLength) { throw new OperationError('Data length cannot be less than tagLength. ') }

[EternalDeiwos]

Ah, I see the problem. Thanks @pierresegonne, nice catch.

https://github.com/anvilresearch/webcrypto/blob/master/src/algorithms/AES-GCM.js#L153

^ should use tagLength instead of algorithm.tagLength

[thelunararmy]

Fixed in 0a10dc74277b9632dbe8ebd213477dd7055b90db

[EternalDeiwos]

@pierresegonne I've just published the fix as v0.7.1. Thanks again and please let us know if you find anything else.