ChatSecure-iOS VS otrv4

https://chatsecure.org/

> ChatSecure is a free and open source messaging app that features OMEMO encryption and OTR encryption over XMPP. You can connect to your existing Google accounts or create new accounts on public XMPP servers (including via Tor), or even connect to your own server for extra security.

> Unlike other apps that keep you stuck in their walled garden, ChatSecure is fully interoperable with other clients that support OMEMO or OTR and XMPP, such as Conversations (Android), CoyIM (Desktop), and more.

iOS: ChatSecure [No Tor connection? That I don't know.]

In this case, I would rather suggest others to use the likes of Element a Matrix client, or e.g. RetroShare, Briar, OnionShare, or e.g. XMPP with the clients like Dino, Conversations, Gajim, ChatSecure.

ChatSecure

I may have missed something here, but the write-up seems to be missing the main problem with OTR, which is that both parties need to be online at the same time to do the key-exchange to set up the session - at least in OTRv3 (https://otr.cypherpunks.ca/Protocol-v3-4.0.0.html)

This is why the Double Ratchet Algorithm was created (back in 2013!) where you prepublish a pool of one-time-keys which can be used to establish sessions without you having to be online - as well as defining how to ratchet the message keys forwards both by new DH exchanges and simple hash ratchets (hence the name Double Ratchet).

OTRv3 has the sole advantage that you can trivially tunnel it over any existing synchronous transport (e.g. an IRC DM), given it doesn't have the concept of setting up sessions asynchronously. However, this is a bit of a moot point these days, given modern messaging systems like Matrix, XMPP and Signal natively support the Double Ratchet via Olm, OMEMO & libsignalprotocol respectively - so OTRv3 really is a bit of a historical curiosity at this point.

Meanwhile OTRv4 does introduce the idea of offline conversation initialisation (https://github.com/otrv4/otrv4/blob/master/otrv4.md#offline-...), but it doesn't seem to have got much traction, relative to the fairly ubiquitous Double Ratchet. (Has anyone seen it in the wild? It looks like coy.im might speak it? https://github.com/otrv4 seems fairly dead :/)

Finally, lots of E2EE research is going into efficient shared ratchets for group communication rather than 1:1 sessions - such as MLS (https://datatracker.ietf.org/wg/mls/about/), DMLS (https://matrix.uhoreg.ca/mls/decentralised.html) and DCGKA (https://www.cylab.cmu.edu/news/2021/11/23-group-messaging.ht...).

AES gets all the marketing glory. You ask the company how are they doing security? Marketing person says: "It's secure we're using AES.". AES is often the only technical word they use when they say it's secure in product brochures because they know this is going to satisfy a clueless CISO with a purchasing budget to cover their behind.

But fast forward from 2009 take a look at OTR and their decision[1] to switch from AES to ChaCha20 (see https://github.com/otrv4/otrv4/blob/master/architecture-deci...) - the whole document is very interesting and pretty brief to highlight why AES might not be the best choice:

> We use ChaCha20 as the encryption stream cipher because it is faster than AES in software-only implementations, it is not sensitive to timing attacks and has undergone rigorous analysis ([3], [4] and [5]). We chose this over AES as future advances in cryptanalysis might uncover security issues with it, its performance on platforms that lack dedicated hardware is slow, and many AES implementations are vulnerable to cache-collision timing attacks [[6]].

But AES is so much faster because some SSD's can offload it to hardware right? See:

256-bit AES encryption broken in SandForce SSD controllers: https://techreport.com/news/23096/256-bit-aes-encryption-bro...

Self-encrypting SSDs can easily be cracked: https://portswigger.net/daily-swig/self-encrypting-ssds-can-...

Crucial and Samsung SSDs' Encryption Is Easily Bypassed: https://www.tomshardware.com/news/crucial-samsung-ssd-encryp...

...

So it seems to me that if I have a large number of architectures and devices my software might be running on which is outside my control then the ability to predict how my crypto implementation will affect the performance of my device is a good enough reason alone to not use AES. But I might be wrong maybe others can throw in some thoughts here.

OTRv3 is definitely not considered secure now, there is an unimplemented (and possibly unfinished) OTRv4 that updates the crypto though:

https://github.com/otrv4/otrv4

So you shouldn't be using Cryptocurrency based communication or PGP at all. You should be using modern deniable protocols like The Signal Protocol (in Signal), OTRv4 (work in progress, no implementations yet), OMEMO (e.g. ChatSecure), and MEGOLM (used by Element).