diff --git a/.changeset/bright-ducks-wonder.md b/.changeset/bright-ducks-wonder.md
new file mode 100644
index 0000000..eafeb75
--- /dev/null
+++ b/.changeset/bright-ducks-wonder.md
@@ -0,0 +1,5 @@
+---
+'@joyid/ckb': minor
+---
+
+feat: Add calculateChallenge and buildSignedTx functions
diff --git a/packages/ckb/src/index.ts b/packages/ckb/src/index.ts
index 4c6657a..b7b9b72 100644
--- a/packages/ckb/src/index.ts
+++ b/packages/ckb/src/index.ts
@@ -263,7 +263,7 @@ export const calculateChallenge = async (
     utils.ckbHash(blockchain.RawTransaction.pack(tx))
   )
   const witnessArgs = blockchain.WitnessArgs.unpack(
-    tx.witnesses[firstWitnessIndex]
+    tx.witnesses[firstWitnessIndex]!
   )
   const emptyWitness = {
     ...witnessArgs,