esp-ena

Implementation of contact tracing with the Covid-19 Exposure Notification API by Apple and Google on an ESP32 (with ESP-IDF). More information about the Covid-19 Exposure Notification at Apple and Google. This is fully compatible with the official API and is meant for people without smartphone or without access to Apples/Googles implementation.

The main source (the Exposure Notification API) is a separate module in components/ena.

This implementation fully covers for the BLE part including the cryptography specifications needed (see Bluetooth Specifications and Cryptography Specifications documents in the links above):

• send beacons
• store TEKs on flash (last 14)
• receive beacons
• received beacons are stored after 5 minutes threshold (storage is limited, ~100k beacons can be stored)
• parse key export binaries as defined in Exposure Key export file format and verification (big thanks to nanopb for making this easier than I thought!)
• calculating risks scores (after adding reported keys and storing exposure information)

Additional features for full ENA device

• RTC support with DS3231
• display support with SSD1306
• interface to
  • set time
  • show exposure status

Extensions planned:

• automatically receive key export from web (will test Corona Warn App)
• send infected status (will test Corona Warn App)
• battery support
• 3d print case
• interface to
  • delete data
  • report infection

Limitations/Problems

• storage only ~2.8mb available
• WiFi or other external connection needed for infections status (auto-connect to open WiFis?)
• obtaining accessibility
• all parameters (scanning time, thresholds etc.)

The following acronyms will be used in code and comments:

• ENA Exposure Notification Api
• ENIN ENIntervalNumber - timestamp with 10 minutes resolution
• TEK Temporary Exposure Key - personal secret key changed every 24h, published when infected
• RPI Rolling Proximity Identifier - send and received identifer changed every 10 minutes
• AEM Associated Encrypted Metadata - send and received metadata

Open questions/problems

• memory is really low with BLE and WiFi enabled, unzipping a Key Export not possible for now, maybe disable BLE service for download.
• service UUID is send reversed, RPI and AEM also send in reverse? Don't know BLE specification enough

How to use

Hardware Required

For now just an ESP32 is required. For full device later RTC (DS3231) and Display (SSD1306) will be required.

Configure the project

idf.py menuconfig

required

• enable bluetooth (BLE)
• add partition-table for storage (currently hardcoded name "ena")
• mbedTLS enable HKDF

recommended

• BLE Scan Duplicate (By Device Address and Advertising Data)

debug options

• Log output set to Debug
• Exposure Notification API / Storage enable Dump storage

Build and Flash

May flash partition table:

idf.py partition_table-flash

Build the project and flash it to the board, then run monitor tool to view serial output:

idf.py -p PORT flash monitor

(Replace PORT with the name of the serial port to use.)

(To exit the serial monitor, type Ctrl-].)

Troubleshooting

Sometimes I get errors from BT-stack of ESP-IDF printed. Didn't affect functionality for now, but I also could not find out what it caused and what it means.

E (909164) BT_HCI: btu_hcif_hdl_command_complete opcode 0x2005 status 0xc

Structure

The project is divided in different components. The main.c just wrap up all components. The Exposure Notification API is in ena module

ena

The ena module contains the main functions of eps-ena with bluetooth scanning and adverting, storing data, handle beacons and check exposure.

• ena-beacons handles scanned data by storing temporary beacons, check for threshold and store beacons permanently
• ena-crypto covers cryptography part (key creation, encryption etc.)
• ena-storage storage part to store own TEKs and beacons
• ena-bluetooth-scan BLE scans for detecting other beacons
• ena-bluetooth-advertise BLE advertising to send own beacons
• ena-exposure decode Key Export, compare with stored beacons, calculate score and risk
• ena run all together and timing for scanning and advertising

ena-cwa

Connection to german Exposure App (Corona Warn App) for download Key Export (and maybe later report infection).

ena-interface

Adds interface functionality via touch pads for control and setup.

i2c-main

Just start I2C driver for display and RTC.

ds3231

I2C driver for a DS3231 RTC

ssd1306

I2C driver for a SSD1306 display.

nanopb

Nanopb for reading Protocol Buffers of Key Export. Including already generated Headers from *.proto files.

miniz

Miniz for unzipping Key Export (not successful for now due to memory limit)

Demo

Demo Video (early stage)