Fix Failures With Prysm Starting Up (#11103)

crypto/ecdsa/utils.go

@@ -25,7 +25,14 @@ func ConvertFromInterfacePrivKey(privkey crypto.PrivKey) (*ecdsa.PrivateKey, err
 }
 
 func ConvertToInterfacePrivkey(privkey *ecdsa.PrivateKey) (crypto.PrivKey, error) {
-	return crypto.UnmarshalSecp256k1PrivateKey(privkey.D.Bytes())
+	privBytes := privkey.D.Bytes()
+	// In the event the number of bytes outputted by the big-int are less than 32,
+	// we append bytes to the start of the sequence for the missing most significant
+	// bytes.
+	if len(privBytes) < 32 {
+		privBytes = append(make([]byte, 32-len(privBytes)), privBytes...)
+	}
+	return crypto.UnmarshalSecp256k1PrivateKey(privBytes)
 }
 
 func ConvertToInterfacePubkey(pubkey *ecdsa.PublicKey) (crypto.PubKey, error) {

crypto/ecdsa/utils_test.go

@@ -2,6 +2,8 @@ package ecdsa
 
 import (
 	"crypto/ecdsa"
+	"crypto/rand"
+	"math/big"
 	"testing"
 
 	"github.com/btcsuite/btcd/btcec/v2"
@@ -26,3 +28,20 @@ func TestConvertToInterfacePubkey(t *testing.T) {
 	origRawKey := gcrypto.FromECDSAPub(pubkey)
 	assert.DeepEqual(t, origRawKey, rawKey)
 }
+
+func TestConvertToInterfacePrivkey_HandlesShorterKeys(t *testing.T) {
+	priv, _, err := crypto.GenerateSecp256k1Key(rand.Reader)
+	assert.NoError(t, err)
+	rawBytes, err := priv.Raw()
+	assert.NoError(t, err)
+	// Zero-out most significant byte so that the big int normalizes
+	// it by removing it.
+	rawBytes[0] = 0
+	privKey := new(ecdsa.PrivateKey)
+	k := new(big.Int).SetBytes(rawBytes)
+	privKey.D = k
+	privKey.Curve = gcrypto.S256()
+	privKey.X, privKey.Y = gcrypto.S256().ScalarBaseMult(rawBytes)
+	_, err = ConvertToInterfacePrivkey(privKey)
+	assert.NoError(t, err)
+}