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RCS is an extension of SMS and has quite literally been "SMS but more capable" from the start. The protocol on the wire looks a lot like MMS over LTE. Registration and communication mostly happens over SIP and RTP like in the latest MMS specs.

The early versions of RCS were barely implemented. Android and iOS didn't bother including clients, carriers didn't bother hosting servers because the spec was optional, and third party applications made by carriers were launched and then died because carriers couldn't explain to customers why their app was better than WhatsApp e.a. for those in the market for alternative messengers.

I think it's safe to say that RCS would've died a quiet death had Google not used it as a basis for their own Hangouts alternative built into their SMS client.

When RCS was first (soft) launched back in 2008, E2EE messaging practically didn't exist. Google slapped E2EE on top when they hosted their own iMessage alternative to bring it into the modern era but the base spec was still "what if MMS wasn't so outdated and restricted".

by microtonal3 hours ago|

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RCS was DOA from day one as far as I'm concerned.

Agreed. Google used a standard that virtually nobody (except some carriers) cared about to get a foot in the door for better interoperability with iPhones, to try to solve an issue that is mostly US-only (green bubble anxiety),

In most of the rest of the world nobody gives a shit about RCS since we have adopted other messengers (than iMessage or SMS/MMS) ages ago, most of which are already end-to-end encrypted.

I understand why GrapheneOS has to spend time on this (the US is a large user base), but it's sad nonetheless.

by HybridStatAnim812 hours ago|

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The RCS spec has encryption in its documentation. I think the current spec version is 4.0?

by Groxx10 hours ago|

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It has it in its current documentation (maybe 3.0 too? I forget, but it's new this year), and Apple and Google have had messages to themselves encrypted for a while (but not to each other, which is what the RCS docs are intended to resolve). It took many years to get it documented though (despite loudly claiming RCS is more secure the whole time), and AFAIK none yet implement it. Definitely none with all the documented things it needs to show to be compliant with the spec I read, e.g. key verification - I certainly don't see any of that in Google's "Messages" app! Though hopefully that will all change.

But honestly, in a non-open ecosystem, can you really trust that the near-exclusive two major players are actually playing by the rules? Apple has been relatively protective of its users on privacy stuff, but I've lost all trust in Google at this point.

by jazzyjackson9 hours ago|

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Yes but there are different specs that “compatible” apps will have to adhere to, basically until everyone is always running auto updating software to the latest version supporting RCS 4.0

Long story short somebody preferred to “ship it” instead of waiting to figure out how to make encryption compatible between iOS and Android. I guess there’s some differences in how the key rings work, but Signal can figure it out and /they’re/ open source so it sucks they ever supported unencrypted messages. They just wanted to say it technically worked for rich text messages and reactions.

by bronson9 hours ago|

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Almost none of my RCS conversations are encrypted. Who cares what's in the spec if nobody uses it?

by glub10 hours ago|

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I don't know much about RCS other than that carriers need to be involved, but there's a way to not involve them, which Google did for a while using some kind of compat-service (jibe or something?), and then they stopped doing it.

Never seen RCS working on any carrier ever since. I don't understand why Google couldn't just continue doing what it was doing. Why require carriers?

by mitxela9 hours ago|

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The intended purpose of RCS was to be federated between carriers, just like SMS. If you centralise it then it's just a worse version of any of Google's abandoned chat apps. But there's a realpolitik reason to insist on centralised RCS: because it's already got the reputation of decentralisation, it makes it look like Google is better than it actually is.

by glub9 hours ago|

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> The intended purpose of RCS was to be federated between carriers, just like SMS.

Oof, so it was essentially destined to fail when the spec was being written.

by mitxela8 hours ago|

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Did SMS fail? Sort of, as it's rarely used, but also not, because it continues to work and it's still the only federated messaging system you can rely on being available on your phone (besides phone calls).

by microtonal3 hours ago|

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SMS was a huge success. For a standard that was defined in 1986 and first rolled out in 1992, it had good longevity and was extremely popular from its introduction until ~2010 [1]. Nearly 20 years is a good run for a technology in a rapidly evolving field. It was also designed in a completely different age when most phones did not have cellular internet and carrier support and federation were the only way to provide reliable person-to-person messaging. Even though the carriers probably dream of reviving SMS as RCS to be more than just pipes for the internet, those days are over.

Google-based RCS is Google coopting an existing standard to get the foot in the door for Apple Messages interoperability. By coopting a standard (rather than pushing yet another Google messenger), they could convince regulators to push Apple towards supporting it. Otherwise RCS is completely irrelevant and if it weren't for Google, it would've been mostly dead.

[1] Yeah, I realize that is was probably used in the US much longer, but that's when it started to dwindle in the rest of the world, where MMS also never really took off.