Outline the Ethereum processor

This was only half-finished to begin with, unfortunately...

processor/ethereum/src/key_gen.rs

@@ -0,0 +1,25 @@
+use ciphersuite::{Ciphersuite, Secp256k1};
+use dkg::ThresholdKeys;
+
+use ethereum_serai::crypto::PublicKey;
+
+pub(crate) struct KeyGenParams;
+impl key_gen::KeyGenParams for KeyGenParams {
+  const ID: &'static str = "Ethereum";
+
+  type ExternalNetworkCiphersuite = Secp256k1;
+
+  fn tweak_keys(keys: &mut ThresholdKeys<Self::ExternalNetworkCiphersuite>) {
+    while PublicKey::new(keys.group_key()).is_none() {
+      *keys = keys.offset(<Secp256k1 as Ciphersuite>::F::ONE);
+    }
+  }
+
+  fn encode_key(key: <Self::ExternalNetworkCiphersuite as Ciphersuite>::G) -> Vec<u8> {
+    PublicKey::new(key).unwrap().eth_repr().to_vec()
+  }
+
+  fn decode_key(key: &[u8]) -> Option<<Self::ExternalNetworkCiphersuite as Ciphersuite>::G> {
+    PublicKey::from_eth_repr(key.try_into().ok()?).map(|key| key.point())
+  }
+}