// Precompiles Below
/// <summary>
/// A precompiled contract which uses v,r,s + hash obtained from the message data to perform elliptic curve public key recovery to obtain a senders address.
/// </summary>
/// <param name="evm">The Ethereum Virtual Machine instance we are executing inside of.</param>
private static EVMExecutionResult Precompile_ECRecover(MeadowEVM evm)
{
// Charge the gas for the precompile operation before processing.
evm.GasState.Deduct(GasDefinitions.GAS_PRECOMPILE_ECRECOVER);
// Obtain a memory representation of our data.
Span <byte> messageData = new Span <byte>(evm.Message.Data);
// We extract our signature information from message data (256-bit each)
Span <byte> hash = messageData.Slice(0, EVMDefinitions.WORD_SIZE);
BigInteger v = BigIntegerConverter.GetBigInteger(messageData.Slice(32, EVMDefinitions.WORD_SIZE));
BigInteger r = BigIntegerConverter.GetBigInteger(messageData.Slice(64, EVMDefinitions.WORD_SIZE));
BigInteger s = BigIntegerConverter.GetBigInteger(messageData.Slice(96, EVMDefinitions.WORD_SIZE));
// Verify we have a low r, s, and a valid v.
if (r >= Secp256k1Curve.N || s >= Secp256k1Curve.N || v < 27 || v > 28)
{
// We failed v,r,s verification, so we stop executing.
return(new EVMExecutionResult(evm, null, true));
}
// Obtain our recovery id from v.
byte recoveryID = EthereumEcdsa.GetRecoveryIDFromV((byte)v);
// Try to get an address from this. If it fails, it will throw an exception.
byte[] senderAddress = null;
try
{
senderAddress = EthereumEcdsa.Recover(hash, recoveryID, r, s).GetPublicKeyHash();
}
catch
{
// Recovery failed, so we stop executing.
return(new EVMExecutionResult(evm, null, true));
}
// The address portion is at the end, and we zero out the leading portion.
for (int i = 0; i < senderAddress.Length - Address.ADDRESS_SIZE; i++)
{
senderAddress[i] = 0;
}
// Return the sender address
return(new EVMExecutionResult(evm, senderAddress, true));
}
