this post was submitted on 03 Oct 2025
616 points (99.2% liked)
Technology
75758 readers
2243 users here now
This is a most excellent place for technology news and articles.
Our Rules
- Follow the lemmy.world rules.
- Only tech related news or articles.
- Be excellent to each other!
- Mod approved content bots can post up to 10 articles per day.
- Threads asking for personal tech support may be deleted.
- Politics threads may be removed.
- No memes allowed as posts, OK to post as comments.
- Only approved bots from the list below, this includes using AI responses and summaries. To ask if your bot can be added please contact a mod.
- Check for duplicates before posting, duplicates may be removed
- Accounts 7 days and younger will have their posts automatically removed.
Approved Bots
founded 2 years ago
MODERATORS
you are viewing a single comment's thread
view the rest of the comments
view the rest of the comments
I don’t use any of these apps, so I’m not quite sure how they work. But couldn’t you just make an app that keeps a local private and public key pair. Then when you send a message (say via regular sms) it includes under the hood your public key. Then the receiver when they reply uses your public key to encrypt the message before sending to you?
Unless the sms infrastructure is going to attempt to detect and reject encrypted content, this seems like it can be achieved without relying on a server backend.
That is how the signal protocol works, it's end to end encrypted with the keys only known between the two ends.
The issue is that servers are needed to relay the connections (they only hold public keys) because your phone doesn't have a static public IP that can reliably be communicated to. The servers are needed to communicate with people as they switch networks constantly throughout the day. And they can block traffic to the relay servers.
Signal does have a censorship circumvention feature in the advanced settings on iOS which may work when this hits provided you already have the app installed. Never had to use it though.
I think they're suggesting doing it on top of SMS/MMS instead of a different transport protocol, like Signal does, which is IP based
Which is what Textsecure was. The precursor to Signal. Signal did it too, but removed it because it confused stupid people.
It is potentially doable:
A short message is 140 bytes of gsm7-bit packed characters (I.e. each character is translated to "ascii" format which only take up 7-bit space, which also is packed together forming unharmonic bytes), so we can probably get away with 160 characters per SMS.
According to crypto.stackexchange, a 2048-bit private key generates a base64 encoded public key of 392 characters.
That would mean 3 SMSs per person you send your public key to. For a 4096-bit private key, this accounts to 5 SMSs.
As key exchange only has to be sent once per contact it sounds totally doable.
After you sent your public key around, you should now be able to receive encrypted short messages from your contacts.
The output length of a ciphertext depends on the key size according to crypto.stackexchange and rfc8017. This means we have 256 bytes of ciphertext for each 2048-bit key encrypted plaintext message, and 512 bytes for 4096-bit keys. Translated into short messages, it would mean 2 or 4 SMSs for each text message respectively, a 1:2, or 1:4 ratio.
Hope you have a good SMS plan 😉
That makes the assumption you want to use your phone number at all. And I'm sure the overhead of encryption would break SMS due to the limits on character counts.
Can't use Signal without a phone number.
You CAN use it to interact with people without them knowing your number. The only current requirement is specific to registration.
I think SimpleX removes the need for static relays.
It was so hard getting people to use signal im imagining thisll never catch on
That’s how signal started way back. Doesn’t work well - sms is terrible.