fix: allow empty public keys when setting signatures (backport #19106) (#19108)

Co-authored-by: Callum Waters <cmwaters19@gmail.com>
Co-authored-by: Julien Robert <julien@rbrt.fr>

CHANGELOG.md

@@ -45,7 +45,8 @@ Ref: https://keepachangelog.com/en/1.0.0/
 
 ### Bug Fixes
 
-* (server) [#18920](https://github.com/cosmos/cosmos-sdk/pull/18920) fixes consensus failure while restart node with wrong `chainId` in genesis.
+* [#19106](https://github.com/cosmos/cosmos-sdk/pull/19106) Allow empty public keys when setting signatures. Public keys aren't needed for every transaction. 
+* (server) [#18920](https://github.com/cosmos/cosmos-sdk/pull/18920) Fixes consensus failure while restart node with wrong `chainId` in genesis.
 
 ## [v0.47.7](https://github.com/cosmos/cosmos-sdk/releases/tag/v0.47.7) - 2023-12-20
 

x/auth/tx/builder.go

@@ -288,14 +288,20 @@ func (w *wrapper) SetSignatures(signatures ...signing.SignatureV2) error {
 	rawSigs := make([][]byte, n)
 
 	for i, sig := range signatures {
-		var modeInfo *tx.ModeInfo
+		var (
+			modeInfo *tx.ModeInfo
+			pubKey   *codectypes.Any
+			err      error
+		)
 		modeInfo, rawSigs[i] = SignatureDataToModeInfoAndSig(sig.Data)
-		any, err := codectypes.NewAnyWithValue(sig.PubKey)
-		if err != nil {
-			return err
+		if sig.PubKey != nil {
+			pubKey, err = codectypes.NewAnyWithValue(sig.PubKey)
+			if err != nil {
+				return err
+			}
 		}
 		signerInfos[i] = &tx.SignerInfo{
-			PublicKey: any,
+			PublicKey: pubKey,
 			ModeInfo:  modeInfo,
 			Sequence:  sig.Sequence,
 		}

x/auth/tx/builder_test.go

@@ -123,6 +123,20 @@ func TestTxBuilder(t *testing.T) {
 	})
 }
 
+func TestSetSignaturesNoPublicKey(t *testing.T) {
+	_, pubkey, _ := testdata.KeyTestPubAddr()
+	txBuilder := newBuilder(nil)
+	sig2 := signing.SignatureV2{
+		Data: &signing.SingleSignatureData{
+			SignMode:  signing.SignMode_SIGN_MODE_DIRECT,
+			Signature: legacy.Cdc.MustMarshal(pubkey),
+		},
+		Sequence: 1,
+	}
+	err := txBuilder.SetSignatures(sig2)
+	require.NoError(t, err)
+}
+
 func TestBuilderValidateBasic(t *testing.T) {
 	// keys and addresses
 	_, pubKey1, addr1 := testdata.KeyTestPubAddr()