diff --git a/pkg/arvo/app/roller-rpc.hoon b/pkg/arvo/app/roller-rpc.hoon
index 43c5643523..b741c15c75 100644
--- a/pkg/arvo/app/roller-rpc.hoon
+++ b/pkg/arvo/app/roller-rpc.hoon
@@ -166,7 +166,8 @@
       %get-nonce               `(nonce id +.params nonce:scry)
       %get-history             `(history id +.params addr:history:scry)
       %get-roller-config       `(get-config id +.params config:scry)
-      %hash-transaction        `(hash-transaction id +.params chain-id:scry)
+      %hash-transaction        `(hash-transaction id +.params chain-id:scry | &)
+      %unsign-transaction      `(hash-transaction id +.params chain-id:scry & |)
       %get-predicted-state     `(get-naive id +.params predicted:scry)
     ==
   --
diff --git a/pkg/arvo/lib/azimuth-roll-rpc.hoon b/pkg/arvo/lib/azimuth-roll-rpc.hoon
index 88caa803e5..f46ff6e7ec 100644
--- a/pkg/arvo/lib/azimuth-roll-rpc.hoon
+++ b/pkg/arvo/lib/azimuth-roll-rpc.hoon
@@ -585,7 +585,7 @@
   [%result id (config:to-json roller-config)]
 ::
 ++  hash-transaction
-  |=  [id=@t params=(map @t json) chain-id=@]
+  |=  [id=@t params=(map @t json) chain-id=@ header=? reverse=?]
   ^-  response:rpc
   ?.  =((lent ~(tap by params)) 4)
     ~(params error:json-rpc id)
@@ -599,9 +599,17 @@
     ~(parse error:json-rpc id)
   =/  tx=(unit tx:naive)  (build-l2-tx u.l2-tx u.from params)
   ?~  tx  ~(parse error:json-rpc id)
+  =/  =octs  (gen-tx-octs:lib u.tx)
   :+  %result  id
-  =-  (hex:to-json 32 (hash-tx:lib p q))
-  (unsigned-tx:lib chain-id u.nonce (gen-tx-octs:lib u.tx))
+  =;  =keccak
+    %+  hex:to-json  32
+    ?.  reverse  keccak
+    (reverse-hash:lib keccak)
+  %-  hash-tx:lib
+  %.  [chain-id u.nonce octs]
+  ?:  header
+    unsigned-tx:lib
+  prepare-for-sig:lib
 ::
 ++  get-naive
   |=  [id=@t params=(map @t json) =^state:naive]
diff --git a/pkg/arvo/lib/naive-transactions.hoon b/pkg/arvo/lib/naive-transactions.hoon
index 7e92947e91..e85deb03eb 100644
--- a/pkg/arvo/lib/naive-transactions.hoon
+++ b/pkg/arvo/lib/naive-transactions.hoon
@@ -203,6 +203,11 @@
   ::
   --
 ::
+++  reverse-hash
+  |=  keccak=@ux
+  ^+  keccak
+  (rev 3 (met 3 keccak) keccak)
+::
 ++  hash-tx  keccak-256:keccak:crypto
 ::
 ++  hash-raw-tx