esp-ena

Implementation of 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 meant for people without smartphone or without smartphones with Apples/Googles implementation.

Demo Video

This implementation covers for now 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)

Features missing for now are:

compare received beacons with infected list
calculating risks scores

Extensions planned:

add RTC (will test DS3231)
add display (will test SSD1306)
interface to
- set time
- delete beacons
- show status
- report infection?
receive infected beacons list (will test Corona Warn App)
send infected status (will test Corona Warn App)
battery support
3d print case

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

now save ENIN for stored beacons (documentation says timestamp), but for infection status ENIN should be enough!?
service UUID is send reversed, must RPI and AEM also beeing send in reverse? Don't know BLE specification enough
fixed change of advertise payload every 10 minutes, random value between ~15 minutes better?

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 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 files

ena-beacon 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 run all together and timing for scanning and advertising
main start and run main program

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