diff --git a/abc/transactions.nim b/abc/transactions.nim
index aca4870..92f65f8 100644
--- a/abc/transactions.nim
+++ b/abc/transactions.nim
@@ -66,3 +66,15 @@ func toBytes*(transaction: Transaction): seq[byte] =
 
 func hash*(transaction: Transaction): TxHash =
   TxHash(sha256.digest(transaction.toBytes))
+
+func hasValidSignature*(transaction: Transaction): bool =
+  if transaction.inputs.len == 0:
+    return false
+
+  var signees: seq[PublicKey]
+  for (_, owner) in transaction.inputs:
+    signees.add(owner)
+  let message = transaction.hash.toBytes
+  let signature = transaction.signature
+  let signee = aggregate(signees)
+  signee.verify(message, signature)
diff --git a/tests/testTransactions.nim b/tests/testTransactions.nim
index 17eea52..1281328 100644
--- a/tests/testTransactions.nim
+++ b/tests/testTransactions.nim
@@ -5,7 +5,9 @@ import ./examples
 
 suite "Transactions":
 
-  let alice, bob = PublicKey.example
+  let aliceKey, bobKey = PrivateKey.example
+  let alice = aliceKey.toPublicKey
+  let bob = bobKey.toPublicKey
 
   test "a genesis transaction can be made":
     let genesis = Transaction.init({alice: 32.u256, bob: 10.u256})
@@ -53,6 +55,20 @@ suite "Transactions":
     transaction.add(sig2)
     check transaction.signature == aggregate(sig1, sig2)
 
+  test "transaction signature can be checked for validity":
+    let genesis = !Transaction.init({alice: 32.u256, bob: 10.u256})
+    check not genesis.hasValidSignature()
+    var transaction = !Transaction.init(
+      {genesis.hash: alice},
+      {alice: 2.u256, bob: 30.u256}
+    )
+    let hash = transaction.hash.toBytes
+    check not transaction.hasValidSignature
+    transaction.add(aliceKey.sign(hash))
+    check transaction.hasValidSignature
+    transaction.add(bobKey.sign(hash))
+    check not transaction.hasValidSignature
+
   test "transaction must have at least one output":
     check Transaction.init([]).isNone