diff --git a/codexvalidator/transaction/serialization.nim b/codexvalidator/transaction/serialization.nim
index 05250d6..46cd492 100644
--- a/codexvalidator/transaction/serialization.nim
+++ b/codexvalidator/transaction/serialization.nim
@@ -36,8 +36,8 @@ func toBytes*(transaction: Transaction): seq[byte] =
     requestId: @(array[32, byte](transaction.requestId)),
     slotIndex: transaction.slotIndex,
     period: transaction.period.uint64,
-    merkleRoot: @(transaction.merkleRoot.toBytesBE()), # TODO: should this not be array[32, byte]?
-    challenge: @(transaction.challenge.toBytesBE()) # TODO ^^^
+    merkleRoot: @(transaction.merkleRoot),
+    challenge: @(transaction.challenge)
   )
   if transaction.kind == TransactionKind.storageProof:
     message.proof = Groth16ProofMessage(
diff --git a/codexvalidator/transaction/transaction.nim b/codexvalidator/transaction/transaction.nim
index dea2e2a..b0c04cb 100644
--- a/codexvalidator/transaction/transaction.nim
+++ b/codexvalidator/transaction/transaction.nim
@@ -17,8 +17,8 @@ type
     requestId: StorageRequestId
     slotIndex: uint32
     period: Period
-    merkleRoot: UInt256
-    challenge: UInt256
+    merkleRoot: array[32, byte]
+    challenge: array[32, byte]
     case kind: TransactionKind
     of storageProof:
       proof: Groth16Proof
@@ -30,8 +30,8 @@ func storageProof*(
   requestId: StorageRequestId,
   slotIndex: uint32,
   period: Period,
-  merkleRoot: UInt256,
-  challenge: UInt256,
+  merkleRoot: array[32, byte],
+  challenge: array[32, byte],
   proof: Groth16Proof
 ): Transaction =
   Transaction(
@@ -49,8 +49,8 @@ func missingProof*(
   requestId: StorageRequestId,
   slotIndex: uint32,
   period: Period,
-  merkleRoot: UInt256,
-  challenge: UInt256,
+  merkleRoot: array[32, byte],
+  challenge: array[32, byte],
 ): Transaction =
   Transaction(
     kind: TransactionKind.missingProof,
@@ -76,10 +76,10 @@ func slotIndex*(transaction: Transaction): uint32 =
 func period*(transaction: Transaction): Period =
   transaction.period
 
-func merkleRoot*(transaction: Transaction): UInt256 =
+func merkleRoot*(transaction: Transaction): array[32, byte] =
   transaction.merkleRoot
 
-func challenge*(transaction: Transaction): UInt256 =
+func challenge*(transaction: Transaction): array[32, byte] =
   transaction.challenge
 
 func proof*(transaction: Transaction): Groth16Proof =
diff --git a/tests/codexvalidator/examples.nim b/tests/codexvalidator/examples.nim
index e87b3da..443b114 100644
--- a/tests/codexvalidator/examples.nim
+++ b/tests/codexvalidator/examples.nim
@@ -47,8 +47,8 @@ proc example*(_: type Transaction): Transaction =
   let requestId = StorageRequestId.example
   let slotIndex = uint32.example
   let period = Period.example
-  let merkleRoot = UInt256.example
-  let challenge = UInt256.example
+  let merkleRoot = array[32, byte].example
+  let challenge = array[32, byte].example
   case kind
   of TransactionKind.missingProof:
     Transaction.missingProof(
diff --git a/tests/codexvalidator/transaction/testSerialization.nim b/tests/codexvalidator/transaction/testSerialization.nim
index 2585ae1..f29c4ec 100644
--- a/tests/codexvalidator/transaction/testSerialization.nim
+++ b/tests/codexvalidator/transaction/testSerialization.nim
@@ -17,8 +17,8 @@ suite "Transaction serialization":
     check protobuf.requestId == array[32, byte](transaction.requestId)
     check protobuf.slotIndex == transaction.slotIndex
     check protobuf.period == transaction.period.uint64
-    check protobuf.merkleRoot == transaction.merkleRoot.toBytesBE()
-    check protobuf.challenge == transaction.challenge.toBytesBE()
+    check protobuf.merkleRoot == array[32, byte](transaction.merkleRoot)
+    check protobuf.challenge == array[32, byte](transaction.challenge)
 
   test "serializes a storage proof with protobuf":
     let proof = Groth16Proof.example
@@ -26,8 +26,8 @@ suite "Transaction serialization":
       StorageRequestId.example,
       uint32.example,
       Period.example,
-      UInt256.example,
-      UInt256.example,
+      array[32, byte].example,
+      array[32, byte].example,
       proof
     )
     let serialized = transaction.toBytes()
diff --git a/tests/codexvalidator/transaction/testTransaction.nim b/tests/codexvalidator/transaction/testTransaction.nim
index 8424e08..e9dc3a8 100644
--- a/tests/codexvalidator/transaction/testTransaction.nim
+++ b/tests/codexvalidator/transaction/testTransaction.nim
@@ -9,8 +9,8 @@ suite "Transaction":
     let requestId = StorageRequestId.example
     let slotIndex = uint32.example
     let period = Period.example
-    let merkleRoot = UInt256.example
-    let challenge = UInt256.example
+    let merkleRoot = array[32, byte].example
+    let challenge = array[32, byte].example
     let proof = Groth16Proof.example
     let transaction = Transaction.storageProof(
       requestId, slotIndex, period, merkleRoot, challenge, proof
@@ -26,8 +26,8 @@ suite "Transaction":
     let requestId = StorageRequestId.example
     let slotIndex = uint32.example
     let period = Period.example
-    let merkleRoot = UInt256.example
-    let challenge = UInt256.example
+    let merkleRoot = array[32, byte].example
+    let challenge = array[32, byte].example
     let transaction = Transaction.missingProof(
       requestId, slotIndex, period, merkleRoot, challenge
     )