DepositInput: Proof of possession, withdrawal credentials (#1675)

* move deposit input to keystore pkg, add proof of possession and withdrawal addr

* Add spec details for deposit input

* Use ssz

* actually use withdrawal key

shared/keystore/BUILD.bazel

@@ -3,6 +3,7 @@ load("@io_bazel_rules_go//go:def.bzl", "go_library", "go_test")
 go_library(
     name = "go_default_library",
     srcs = [
+        "deposit_input.go",
         "keccak256.go",
         "key.go",
         "keystore.go",
@@ -11,7 +12,10 @@ go_library(
     importpath = "github.com/prysmaticlabs/prysm/shared/keystore",
     visibility = ["//visibility:public"],
     deps = [
+        "//proto/beacon/p2p/v1:go_default_library",
         "//shared/bls:go_default_library",
+        "//shared/params:go_default_library",
+        "//shared/ssz:go_default_library",
         "@com_github_pborman_uuid//:go_default_library",
         "@org_golang_x_crypto//pbkdf2:go_default_library",
         "@org_golang_x_crypto//scrypt:go_default_library",
@@ -22,14 +26,19 @@ go_library(
 go_test(
     name = "go_default_test",
     srcs = [
+        "deposit_input_test.go",
         "key_test.go",
         "keystore_test.go",
     ],
     embed = [":go_default_library"],
     deps = [
+        "//proto/beacon/p2p/v1:go_default_library",
         "//shared/bls:go_default_library",
         "//shared/bytesutil:go_default_library",
+        "//shared/params:go_default_library",
+        "//shared/ssz:go_default_library",
         "//shared/testutil:go_default_library",
+        "@com_github_gogo_protobuf//proto:go_default_library",
         "@com_github_pborman_uuid//:go_default_library",
     ],
 )

shared/keystore/deposit_input.go

@@ -0,0 +1,51 @@
+package keystore
+
+import (
+	"bytes"
+
+	pb "github.com/prysmaticlabs/prysm/proto/beacon/p2p/v1"
+	"github.com/prysmaticlabs/prysm/shared/params"
+	"github.com/prysmaticlabs/prysm/shared/ssz"
+)
+
+// DepositInput for a given key. This input data can be used to when making a
+// validator deposit. The input data includes a proof of possession field
+// signed by the deposit key.
+//
+// Spec details about general deposit workflow:
+//   To submit a deposit:
+//
+//   - Pack the validator's initialization parameters into deposit_input, a DepositInput SSZ object.
+//   - Set deposit_input.proof_of_possession = EMPTY_SIGNATURE.
+//   - Let proof_of_possession be the result of bls_sign of the hash_tree_root(deposit_input) with domain=DOMAIN_DEPOSIT.
+//   - Set deposit_input.proof_of_possession = proof_of_possession.
+//   - Let amount be the amount in Gwei to be deposited by the validator where MIN_DEPOSIT_AMOUNT <= amount <= MAX_DEPOSIT_AMOUNT.
+//   - Send a transaction on the Ethereum 1.0 chain to DEPOSIT_CONTRACT_ADDRESS executing deposit along with serialize(deposit_input) as the singular bytes input along with a deposit amount in Gwei.
+//
+// See: https://github.com/ethereum/eth2.0-specs/blob/dev/specs/validator/0_beacon-chain-validator.md#submit-deposit
+func DepositInput(depositKey *Key, withdrawalKey *Key) (*pb.DepositInput, error) {
+	di := &pb.DepositInput{
+		Pubkey:                      depositKey.PublicKey.Marshal(),
+		WithdrawalCredentialsHash32: withdrawalCredentialsHash(withdrawalKey),
+	}
+
+	buf := new(bytes.Buffer)
+	if err := ssz.Encode(buf, di); err != nil {
+		return nil, err
+	}
+	di.ProofOfPossession = depositKey.SecretKey.Sign(buf.Bytes(), params.BeaconConfig().DomainDeposit).Marshal()
+
+	return di, nil
+}
+
+// withdrawalCredentialsHash forms a 32 byte hash of the withdrawal public
+// address.
+//
+// The specification is as follows:
+//   withdrawal_credentials[:1] == BLS_WITHDRAWAL_PREFIX_BYTE
+//   withdrawal_credentials[1:] == hash(withdrawal_pubkey)[1:]
+// where withdrawal_credentials is of type bytes32.
+func withdrawalCredentialsHash(withdrawalKey *Key) []byte {
+	h := Keccak256(withdrawalKey.PublicKey.Marshal())
+	return append([]byte{params.BeaconConfig().BLSWithdrawalPrefixByte}, h...)[:32]
+}

shared/keystore/deposit_input_test.go

@@ -0,0 +1,50 @@
+package keystore_test
+
+import (
+	"bytes"
+	"crypto/rand"
+	"testing"
+
+	"github.com/gogo/protobuf/proto"
+	pb "github.com/prysmaticlabs/prysm/proto/beacon/p2p/v1"
+	"github.com/prysmaticlabs/prysm/shared/bls"
+	"github.com/prysmaticlabs/prysm/shared/keystore"
+	"github.com/prysmaticlabs/prysm/shared/params"
+	"github.com/prysmaticlabs/prysm/shared/ssz"
+)
+
+func TestDepositInput_GeneratesPb(t *testing.T) {
+	k1, err := keystore.NewKey(rand.Reader)
+	if err != nil {
+		t.Fatal(err)
+	}
+	k2, err := keystore.NewKey(rand.Reader)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	result, err := keystore.DepositInput(k1, k2)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !bytes.Equal(result.Pubkey, k1.PublicKey.Marshal()) {
+		t.Errorf("Mismatched pubkeys in deposit input. Want = %x, got = %x", result.Pubkey, k1.PublicKey.Marshal())
+	}
+
+	sig, err := bls.SignatureFromBytes(result.ProofOfPossession)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Verify that the proof of possession is a signed copy of the input data.
+	proofOfPossessionInputPb := proto.Clone(result).(*pb.DepositInput)
+	proofOfPossessionInputPb.ProofOfPossession = nil
+	buf := new(bytes.Buffer)
+	if err := ssz.Encode(buf, proofOfPossessionInputPb); err != nil {
+		t.Fatal(err)
+	}
+
+	if !sig.Verify(buf.Bytes(), k1.PublicKey, params.BeaconConfig().DomainDeposit) {
+		t.Error("Invalid proof of proofOfPossession signature")
+	}
+}

shared/params/config.go

@@ -129,13 +129,14 @@ var defaultBeaconConfig = &BeaconChainConfig{
 	ForkChoiceBalanceIncrement: 1 * 1e9,
 
 	// Initial value constants.
-	GenesisForkVersion: 0,
-	GenesisSlot:        1 << 63,
-	GenesisEpoch:       1 << 63 / 64,
-	GenesisStartShard:  0,
-	FarFutureEpoch:     1<<64 - 1,
-	ZeroHash:           [32]byte{},
-	EmptySignature:     [96]byte{},
+	GenesisForkVersion:      0,
+	GenesisSlot:             1 << 63,
+	GenesisEpoch:            1 << 63 / 64,
+	GenesisStartShard:       0,
+	FarFutureEpoch:          1<<64 - 1,
+	ZeroHash:                [32]byte{},
+	EmptySignature:          [96]byte{},
+	BLSWithdrawalPrefixByte: byte(0),
 
 	// Time parameter constants.
 	SecondsPerSlot:               6,

validator/accounts/BUILD.bazel

@@ -6,7 +6,6 @@ go_library(
     importpath = "github.com/prysmaticlabs/prysm/validator/accounts",
     visibility = ["//validator:__subpackages__"],
     deps = [
-        "//proto/beacon/p2p/v1:go_default_library",
         "//shared/keystore:go_default_library",
         "//shared/params:go_default_library",
         "//shared/ssz:go_default_library",

validator/accounts/account.go

@@ -8,7 +8,6 @@ import (
 
 	"github.com/prysmaticlabs/prysm/shared/params"
 
-	pb "github.com/prysmaticlabs/prysm/proto/beacon/p2p/v1"
 	"github.com/prysmaticlabs/prysm/shared/keystore"
 	"github.com/prysmaticlabs/prysm/shared/ssz"
 	"github.com/sirupsen/logrus"
@@ -73,12 +72,10 @@ func NewValidatorAccount(directory string, password string) error {
 		validatorKeyFile,
 	).Info("Keystore generated for validator signatures at path")
 
-	data := &pb.DepositInput{
-		Pubkey:                      validatorKey.SecretKey.PublicKey().Marshal(),
-		ProofOfPossession:           []byte("pop"),
-		WithdrawalCredentialsHash32: []byte("withdraw"),
+	data, err := keystore.DepositInput(validatorKey, shardWithdrawalKey)
+	if err != nil {
+		return fmt.Errorf("unable to generate deposit data: %v", err)
 	}
-
 	serializedData := new(bytes.Buffer)
 	if err := ssz.Encode(serializedData, data); err != nil {
 		return fmt.Errorf("could not serialize deposit data: %v", err)