proto: add proto files for ibc unblock (#4853)

## Description

these proto files are meant to help unblock ibc in their quest of migrating the ibc module to proto.

Closes: #XXX

crypto/encoding/codec.go

@@ -0,0 +1,75 @@
+package encoding
+
+import (
+	"errors"
+	"fmt"
+
+	"github.com/tendermint/tendermint/crypto"
+	"github.com/tendermint/tendermint/crypto/ed25519"
+	pc "github.com/tendermint/tendermint/proto/crypto/keys"
+)
+
+// PubKeyToProto takes crypto.PubKey and transforms it to a protobuf Pubkey
+func PubKeyToProto(k crypto.PubKey) (pc.PublicKey, error) {
+	var kp pc.PublicKey
+	switch k := k.(type) {
+	case ed25519.PubKeyEd25519:
+		kp = pc.PublicKey{
+			Sum: &pc.PublicKey_Ed25519{
+				Ed25519: k[:],
+			},
+		}
+	default:
+		return kp, fmt.Errorf("toproto: key type %v is not supported", k)
+	}
+	return kp, nil
+}
+
+// PubKeyFromProto takes a protobuf Pubkey and transforms it to a crypto.Pubkey
+func PubKeyFromProto(k pc.PublicKey) (crypto.PubKey, error) {
+	switch k := k.Sum.(type) {
+	case *pc.PublicKey_Ed25519:
+		if len(k.Ed25519) != ed25519.PubKeyEd25519Size {
+			return nil, fmt.Errorf("invalid size for PubKeyEd25519. Got %d, expected %d",
+				len(k.Ed25519), ed25519.PubKeyEd25519Size)
+		}
+		var pk ed25519.PubKeyEd25519
+		copy(pk[:], k.Ed25519)
+		return pk, nil
+	default:
+		return nil, fmt.Errorf("fromproto: key type %v is not supported", k)
+	}
+}
+
+// PrivKeyToProto takes crypto.PrivKey and transforms it to a protobuf PrivKey
+func PrivKeyToProto(k crypto.PrivKey) (pc.PrivateKey, error) {
+	var kp pc.PrivateKey
+	switch k := k.(type) {
+	case ed25519.PrivKeyEd25519:
+		kp = pc.PrivateKey{
+			Sum: &pc.PrivateKey_Ed25519{
+				Ed25519: k[:],
+			},
+		}
+	default:
+		return kp, errors.New("toproto: key type is not supported")
+	}
+	return kp, nil
+}
+
+// PrivKeyFromProto takes a protobuf PrivateKey and transforms it to a crypto.PrivKey
+func PrivKeyFromProto(k pc.PrivateKey) (crypto.PrivKey, error) {
+	switch k := k.Sum.(type) {
+	case *pc.PrivateKey_Ed25519:
+
+		if len(k.Ed25519) != ed25519.PubKeyEd25519Size {
+			return nil, fmt.Errorf("invalid size for PubKeyEd25519. Got %d, expected %d",
+				len(k.Ed25519), ed25519.PubKeyEd25519Size)
+		}
+		var pk ed25519.PrivKeyEd25519
+		copy(pk[:], k.Ed25519)
+		return pk, nil
+	default:
+		return nil, errors.New("fromproto: key type not supported")
+	}
+}