/// <summary>
/// Recovers the ephemeral key used to sign the transformed nonce in the authentication data.
/// Throws an exception if the recovered key is invalid, or could not be recovered.
/// </summary>
/// <param name="receiverPrivateKey">The private key of the receiver used to generate the shared secret.</param>
/// <returns>Returns the remote ephemeral public key for the keypair which signed this authentication data.</returns>
public virtual (EthereumEcdsa remoteEphemeralPublicKey, uint?chainId) RecoverDataFromSignature(EthereumEcdsa receiverPrivateKey)
{
// Create an EC provider with the given public key.
EthereumEcdsa publicKey = EthereumEcdsa.Create(PublicKey, EthereumEcdsaKeyType.Public);
// Generate the shared secret using ECDH between our local private key and this remote public key
byte[] ecdhKey = receiverPrivateKey.ComputeECDHKey(publicKey);
// Obtain our transformed nonce data.
byte[] transformedNonceData = GetTransformedNonce(ecdhKey);
// We want our signature in r,s,v format.
BigInteger ecdsa_r = BigIntegerConverter.GetBigInteger(R, false, 32);
BigInteger ecdsa_s = BigIntegerConverter.GetBigInteger(S, false, 32);
(byte recoveryId, uint?chainId) = EthereumEcdsa.GetRecoveryAndChainIDFromV(V);
// Recover the public key from the data provided.
EthereumEcdsa remoteEphemeralPublickey = EthereumEcdsa.Recover(transformedNonceData, recoveryId, ecdsa_r, ecdsa_s);
// Verify the key is valid
// Return the ephemeral key
return(remoteEphemeralPublickey, chainId);
}
// 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.GetRecoveryAndChainIDFromV((byte)v).recoveryId;
// 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));
}
public void SignAndVerify(bool useBouncyCastle)
{
// Generate ECDSA keypair, compute a hash, sign it, then recover the public key from the signature and verify it matches.
EthereumEcdsa provider;
if (useBouncyCastle)
{
provider = EthereumEcdsaBouncyCastle.Generate(new SystemRandomAccountDerivation());
}
else
{
provider = EthereumEcdsaNative.Generate(new SystemRandomAccountDerivation());
}
byte[] hash = KeccakHash.ComputeHashBytes(new byte[] { 11, 22, 33, 44 });
(byte RecoveryID, BigInteger r, BigInteger s)signature = provider.SignData(hash);
EthereumEcdsa recovered = EthereumEcdsa.Recover(hash, signature.RecoveryID, signature.r, signature.s);
Assert.True(provider.GetPublicKeyHash().ValuesEqual(recovered.GetPublicKeyHash()));
}