Draft "CoSMS" binding to relay cargo via SMS

[gnarea]

Executive summary

We could use SMS to send and receive high-priority Relaynet parcels wrapped in cargo (to preserve privacy), since SMS sometimes remains operational (temporarily) during Internet blackouts.

The problem you're trying to solve

We're not taking advantage of SMS to send and receive data.

The solution you'd like

Use SMS to send and receive only parcels with the highest priority, but do it sparingly because SMS has a poor throughput and the end user may have to pay extra for each SMS: It'll take 3+ SMSs to send a single cargo, depending on the amount of data being sent.

Consequently, before we can do this, we need to do the following:

• Implement the Quality of Service extension.
• Replace RSA key pairs with Ed25519. Alternatively, get the Relaynet-Internet Gateway to cache all the certificates in the PDA/CDA chains from that specific private gateway, so that the parcels and cargo won't have to include the certificates (which often make up most of the data).
• Consider whether can make CMS SignedData/EnvelopedData values leaner. Alternatively, consider ditching CMS/DER altogether and only transfer the ciphertext plus some minimal metadata (unlikely to make a big difference but worth trying).

Relaynet-Internet Gateway operators like Relaycorp will have to use a service like Twilio to do this.

Alternatives you've considered

Phone calls.