Signing transactions

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Ethereum

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Overview

Before a transaction can be sent to the Ethereum network, it must be signed and formatted into a raw ETH transaction.

A code example using the ethers-core Rust library to sign and format an ETH EIP-1559 transaction can be found below:

#[update(guard = "caller_is_not_anonymous")]
async fn sign_transaction(req: SignRequest) -> String {
    use ethers_core::types::transaction::eip1559::Eip1559TransactionRequest;
    use ethers_core::types::Signature;

    const EIP1559_TX_ID: u8 = 2;

    let caller = ic_cdk::caller();

    let data = req.data.as_ref().map(|s| decode_hex(s));

    let tx = Eip1559TransactionRequest {
        chain_id: Some(nat_to_u64(&req.chain_id)),
        from: None,
        to: Some(
            Address::from_str(&req.to)
                .expect("failed to parse the destination address")
                .into(),
        ),
        gas: Some(nat_to_u256(&req.gas)),
        value: Some(nat_to_u256(&req.value)),
        nonce: Some(nat_to_u256(&req.nonce)),
        data,
        access_list: Default::default(),
        max_priority_fee_per_gas: Some(nat_to_u256(&req.max_priority_fee_per_gas)),
        max_fee_per_gas: Some(nat_to_u256(&req.max_fee_per_gas)),
    };

    let mut unsigned_tx_bytes = tx.rlp().to_vec();
    unsigned_tx_bytes.insert(0, EIP1559_TX_ID);

    let txhash = keccak256(&unsigned_tx_bytes);

    let (pubkey, signature) = pubkey_and_signature(&caller, txhash.to_vec()).await;

    let signature = Signature {
        v: y_parity(&txhash, &signature, &pubkey),
        r: U256::from_big_endian(&signature[0..32]),
        s: U256::from_big_endian(&signature[32..64]),
    };

    let mut signed_tx_bytes = tx.rlp_signed(&signature).to_vec();
    signed_tx_bytes.insert(0, EIP1559_TX_ID);

    format!("0x{}", hex::encode(&signed_tx_bytes))
}

Next steps

Now that your transaction is signed, it can be submitted to Ethereum to be executed.

Learn how to submit Ethereum transactions.