Subject: Re: [Cfrg] [TLS] 3DES diediedie

From: "Blumenthal, Uri - 0553 - MITLL" <[email-masked]>
Date: Thu, 1 Sep 2016 13:53:00 +0000

"Some cents" on a single device usually turn into noticeable bucks‎ when the number of the manufactured devices and their accumulated costs pile up. Rather obvious?

Sent from my BlackBerry 10 smartphone on the Verizon Wireless 4G LTE network.
  Original Message  
From: Joachim Strömbergson
Sent: Thursday, September 1, 2016 03:50
To: Hilarie Orman
Cc: [email-masked]; [email-masked]
Subject: Re: [Cfrg] [TLS] 3DES diediedie

Aloha!

Hilarie Orman wrote:
> An ARM is far too much hardware to throw at "read sensor/munge
> data/send data".

No, they are not. The Cortex M0+ is aimed at these kinds of very simple
systems that runs for many years on a single battery.

Look at the STM32L0 series from ST for example. These devices can run on
energy harvesting and very tiny physically and very, very cheap (ten-ish
cents in high volume):

http://www.st.com/content/st_com/en/products/microcontrollers/stm32-32-bit-arm-cortex-mcus/stm32l0-series.html?querycriteria=productId=SS1817

The STM32L021 has an AES-128 core. Not very fast (200+ cycles), but
several times faster than SW. You can also run the AES core wile the CPU
core is in power save mode.

Another example is the Zero Gecko from Silicon Labs. Same price range, a
huge number of power modes. And an AES core that is really fast. 50+
cycles for AES-128, which basically means 4 cycles/round (which implies
4 S-boxes)

https://www.silabs.com/products/mcu/32-bit/efm32-zero-gecko/pages/efm32-zero-gecko.aspx

Pre-shared key is whats easiest. But I've implemented Curve25519 for key
exchange on the STM32 device and can achieve <1 sec performance with
about 1 kByte RAM and 8 kByte code. I'm sure Peter Schwabe has some much
better results.

Yes, you can limit yourself to an 8-bit MCU and shave off some cents and
a little bit of power. But for most applications I see, a Cortex M0+
meets technical and commercial requirements too.

- -- 
Med vänlig hälsning, Yours

Joachim Strömbergson - Alltid i harmonisk svängning.
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Joachim Strömbergson Secworks AB [email-masked]
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