[Cryptography] Signal hypothetical use case becomes practical since cellular providers have started censoring private text messages

John Levine johnl at iecc.com
Fri Dec 31 22:36:22 EST 2021

It appears that Whitfield Diffie <whitfield.diffie at gmail.com> said:
>    I am shocked to learn that they are allowed to censor anything.  This
>is a personal message, not a broadcast.  Are they allowed to censor email?
>Telephone conversation?

Technically speaking, no, since censorship is a government activity
while e-mail and phone providers are private entities. But they block
tons of e-mail and increasing amounts of voice calls for spam

About 90% of e-mail messages are spam, a number that hasn't changed
much in recent years. Every mail provider does spam and malware
filtering; if they didn't your mail would be unusuable because you
couldn't find the trickle of real mail in the mountains of garbage.
Look at any mail provider's terms of service and you will find that
they don't promise to deliver anything. There's no way they could.

Historically since telcos are common carriers they have been required
to complete every call, but that has also changed in recent years due
to the deluge of VoIP spam. The IETF's STIR and SHAKEN puts a
(obCryptography) digital signature in each SIP call header so that
recipient systems can see whether the call is likely to really be from
the putative calling number. Calls that aren't are now marked
SUSPECTED SPAM and starting soon, won't be delivered at all.

The FCC has pushed telcos to do this in response to many complaints about
voice spam.  See, for example:




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