esp-ena

Implementation of the Covid19 Exposure Notification API by Apple and Google on an ESP32. More information about the Covid19 Exposure Notification at Apple and Google. This is meant for people without smartphone or without smartphones with Apples/Googles implementation.

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 tokens
• store send tokens on flash (last 14 tokens)
• receive tokens
• received tokens are stored after 5 minutes threshold (storage is limited, ~100k tokens can be stored)

Features missing for now are:

• compare received tokens with infected list
• calculating risks scores

Extensions planned:

• add RTC (will test DS3231)
• add display (will test SSD1306)
• interface to
  • set time
  • delete tokens
  • show status
  • report infection?
• receive infected token list for Germany (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 detection (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)

Build and 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-].)

Example Output

For now some debug outputs are set. Besides, after each scan a CSV output is printed with stored TEKs, temporary detections (RPI) and full detections (RPI)

I (1201484) ESP-ENA-advertise: payload for ENIN 2657432
D (1201494) ESP-ENA-advertise: 0x3ffbb6c4   02 01 1a 03 03 6f fd 17  16 6f fd 9a ee 95 9a 24  |.....o...o.....$|
D (1201494) ESP-ENA-advertise: 0x3ffbb6d4   f0 f9 8e 56 0f 6d 68 5f  ac 12 e5 7f 94 a1 47     |...V.mh_......G|
I (1201524) ESP-ENA-scan: start scanning...
D (1202224) ESP-ENA-detection: New temporary detection at 0 with timestamp 1594459201
D (1202224) ESP-ENA-detection: 19 05 e3 3a 73 16 4e 74 2d 48 fc 0c 41 f6 26 3b 
D (1202234) ESP-ENA-detection: 5e 7d a9 48 
D (1202234) ESP-ENA-detection: RSSI -79
#,enin,tek
0,2657430,d5 13 92 b2 44 e4 7e b6 ca a7 20 c4 f 37 c0 1c
#,timestamp,rpi,aem,rssi
0,1594459201,19 5 e3 3a 73 16 4e 74 2d 48 fc c 41 f6 26 3b,5e 7d a9 48,-79
#,enin,rpi,aem,rssi
0,2657430,c7 2e b6 66 af 84 42 db b d1 a 0 f1 fd 86 2,4d 1 b2 d1,-76
1,2657431,19 5 e3 3a 73 16 4e 74 2d 48 fc c 41 f6 26 3b,5e 7d a9 48,-76
I (1231754) ESP-ENA-scan: finished scanning...

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-crypto covers cryptography part (key creation, encryption etc.)
• ena-storage storage part to store own TEKs and detections
• ena-detection handles scanned data by storing temporary detections, check for threshold and store full detections
• ena-bluetooth-scan BLE scans for detecting other tokens
• ena-bluetooth-advertise BLE advertising to send own tokens
• ena run all together and timing for scanning and advertising
• main start and run main program