Solution to submit transaction to ETH chain using microcontroller like ESP8266 or ESP32

Inplemented extrinsic methods

Transfer balance as Raw Transaction
Smart contracts: ref. libraries/contracts/README.md

Implementetiaon

Refference pyton scripts: web3eth.py (high level) and rlp4eth.py (low level, based on secp256k1 library for ECDSA sign)
C++ Linux (supports micro-ECC and secp256k1) and ESP platform (supports micro-ECC, secp256k1 and Trezor).
Library for ECDSA is defined in Defines.h:
ESP8266: micro-ECC,
ESP32: micro-ECC, secp256k1 and Trezor,
Linux: micro-ECC and secp256k1 (Trezor is not supported).
micro-ECC based implementation is the most robust (EPS32 with secp256k1 and Trezor reboots after some count of transactions).

Dependency

Python: imported libs in scripts
C++: sudo apt install libsecp256k1-dev libjsoncpp-dev

Build

1. Linux (ref. Deploy section to proper configuration):
   run build script: ./build.sh
2. ESP32 (Arduino IDE under Windows) or arduino-cli (as Linux command line, ref to CI sripts)

Testing chain: ganache

Install ganache-cli, note: maybe need to install proper vesion of nmp
Run ganache as deterministic chain node (with the same private key every new start:)
ganache-cli -d -h 0.0.0.0 In case of smart contract usage is needed to upload it, i.e. by Remix to local host node.

Test cases:

1. Test on Linux and python implementation (ref. to cripts code):
2. Test on Linux C++ implementation:
   build linux (using ./build.sh) binary and then run python script:
   python3 ethraw.py [rpcId] [ethHost] [privKey]
   i.e.
   python3 ethraw.py 1 http://192.168.0.106:8545 4f3edf983ac636a65a842ce7c78d9aa706d3b113bce9c46f30d7d21715b23b1d
3. Test with ESP implementation:
   Ref. to deploy section.
   Note: ganache chain node and ESP should be in the same subnet
4. Unit tests for RPL and ABI serialization:
   python3 test_rpl.py

CI

There are in .github/workflows/ files:
web3esp.yml
to check in local PC run:
act -j esp

Deploy to ESP

1. Set up in DefineEth.h Linux or ESP mode (target ESP8266 or ESP32), proper ECDSA library and it entropy settings.
2. Set up in DefineEth.h ethereum host address and port, i.e. ETHURL "http://192.168.0.106:8545"
3. Copy template Private.h to PrivateEth_dummy.h set proper STASSID, STAPSK and PRIV_ETH_KEY macro definitionss.
4. Uncomment #define DUMMY_KEYS in Arduino ino file to use own credentials from PrivateEth_dummy.h
5. Build for selected target.
6. Flash target.
7. Run and check output in command line terminalr or in serial monitor.

Online checkers:

https://www.ethereumdecoder.com/ - to check transaction online
https://emn178.github.io/online-tools/keccak_256.html -- check online as hex

https://www.ethereumdecoder.com/ -- RPL online decoder to check
https://toolkit.klaytn.foundation/transaction/rlpDecode -- online rlp
https://codechain-io.github.io/rlp-debugger/ -- onlie rlp
https://toolkit.abdk.consulting/ethereum

Some of main used sources:

https://github.com/brainhub/SHA3IUF -- keccak-256 hash
https://github.com/kmackay/micro-ecc -- modified to provide v for recid calculation
https://github.com/diybitcoinhardware/secp256k1-embedded -- secp256k1 port for small embedded systems
https://github.com/kvhnuke/Ethereum-Arduino -- RLP for ESP
https://github.com/AlphaWallet/Web3E -- Trezor for ESP
https://github.com/mhw0/libethc -- secp256k1 wrapper