[Cryptography] Brainstorming for encrypted text messaging ideas...with a twist

[Tom Mitchell]

On Thu, Jun 15, 2017 at 7:32 PM, Grant Schultz <gschultz at kc.rr.com> wrote:
> I'm trying to brainstorm ideas for uncrackable encrypted text messaging over
> smartphones.  Since any software running on the phone is subject to being
> hacked, the encryption would have to take place on a separate device before
> the message was entered on the phone.

The uncrackable is difficult.
A single cell phone is difficult.   However two devices could be less hackable.
An old cell phone can be side loaded with an application in developer mode
and kept in airplane mode and air gaped.

Old device, enter text, encrypt and generate a QR code block.
A second phone can see the QR code block, cross the air gap
with the camera., convert to  characters and transmit.  Reception
of an encrypted  message uses a generated QR code that the receivers old
cell phone can see with its camera crossing the air gap to be decrypted.

Key management can be facilitated with paper QR code sheets.
A sheet of QR codes can be printed with a layout kin to
a phone key pad and by selecting four or more (N) based
on a pin known only to the sender the secret reloaded.
No encryption key is intact on a single QR block.   Something physical and
also something known.

Permutations of hardware allow keyboard and screen of a laptop to replace the
old phone  QR code generation and also shared and private secret management.

Airplane mode allows an air gap, QR blocks facilitate data entry
across an air gap.

Both Google and Microsoft use web displayed QR blocks to
interact with their multi factor authentication tools.
The number of characters is large enough to be interesting.

Newer devices are improving in some ways but mixing old and new complicates
hacking and lower cost.

The messages in transit need not be generated with air gaped
safety and complexity to allow a larger market and user community.
Simple copy and paste can replace the QR code air gap step.

Key management is key.

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