[aerogear-dev] iOS Crypto questions

[Douglas Campos]

On Fri, Oct 18, 2013 at 04:56:24PM +0200, Corinne Krych wrote:
> Hello All
> 
> I've just updated the crypto iOS API documentation
> https://github.com/corinnekrych/aerogear.org/blob/77ab01e16bd385c7d8a507dfb4b0a6838c4d6c13/docs/specs/aerogear-crypto.md#api-draft-0-2
> 
> I would like to discuss with you the actual symmetric encryption method in the API. Atm, we have:
> => Java:
> cryptoBox.encrypt(IV, message);
> => objective-C
> NSData* encryptedData = [cryptoBox encrypt:dataToEncrypt IV:encryptionSalt];

Sorry for breaking the flow, but it's really really important to
distinguish an IV from a salt - they're different things for different
purposes.

> => JavaScript
> AeroGear.encrypt( options );
> 
> I think JavaScript grouping everything (key, IV, data to encrypt) in
> options is not the best approach but I like the encrypt method with
> only one argument. I rather have options containing key/IV information
> and have a separate method encrypt that takes the message to encrypt. 

This is a place where we respect each language's idiomatism - JS is this
way, and I don't think it's a good idea to aim for a one-size-fits-all
in this case.

> 
> Something like:
> 
> => Java:
> CryptoBox cryptoBox = new CryptoBox(new PrivateKey(SOME_SECRET_KEY), IV);

Like I replied to Christos, the IV has to be unique and non-predictable,
so this isn't an option.

I'm almost 100% sure I'll turn this into factory calls too, stay tuned.

> cryptoBox.encrypt(message);

It's really common to setup a session based on a key, then just go
encrypting stuff with it. So reusing the `CryptoBox` instance is
something that is probably a good idea.

> => objective-C
> cryptoBox = [[AGCryptoBox alloc] initWithKey:key salt:encryptionSalt initializationVector:vector]];
> NSData* encryptedData = [cryptoBox encrypt:dataToEncrypt];

...

> => JavaScript
> var options = {
>     IV: superRandomInitializationVector,
>     AAD: "whateverAuthenticatedData",
>     key: generatedKey
> };
> AeroGear.setOptions(options);
> AeroGear.encrypt(message);

That would be a global setting - just think what happens if you create a
secure chat app and each user uses a different key... this fails.

-- 
qmx
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