Hashs & MAC chunk by chunk

[tex0l]

Hi!

Thank you for your amazing reactivity :)!

I was wondering if you were planning to expose a way to calculate MACs and hashes in multiple stages:

• creation to set up the mac or hash object;
• update to add the chunks to and update its internal state;
• digest to finalize and return the mac or hash value.

We use it to calculate MACs of very large files without passing an ArrayBuffer of the file: https://github.com/seald/sscrypto/blob/c54c0fdb9f9cd4b311f031a9db1967bfd330b6f7/src/forge/aes.ts#L73

We can trick it for AES CBC without having to remember an internal state, but for hashes and MACs it is impossible (as far as I know).

Would you consider implementing such a feature? May we help on this?

[JiriHoffmann]

Right, that would be the ideal solution and how other libraries do it as well. The issue is that my current knowledge of the JSI Host Objects is not the greatest. I just didn't have enough time to look into it for now.

Cryptopp also does it this way, example from the [wiki]:(https://www.cryptopp.com/wiki/HMAC)

HMAC<SHA1> hmac(k, sizeof(k));
hmac.Update(m, sizeof(m));

byte d[HMAC<SHA1>::DIGESTSIZE];
hmac.Final(d);

If you want to help, I would be more than happy to include it in the code.

[JiriHoffmann]

Hey @tex0l! Progressive hashing is up on master. Note that I changed hashFunctions to just hash. HMAC & CMAC will be next.

Snippet from example:

react-native-cryptopp/example/src/App.tsx

Lines 120 to 122 in 19353af

	const hash = Cryptopp.hash.create('BLAKE2b');
	Array.from(str).forEach((c) => hash.update(c));
	const BLAKE2b_progressive = hash.finalize();

[tex0l]

On this, I managed to implement an HMAC in JS with the progressive SHA256 ;) it works perfectly!