diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,11 @@
 The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/)
 and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.html).
 
+## 0.9.1
+### Added
+- Add a function to produce a structured signature over a transaction.
+- Enable `-O2` optimisations.
+
 ## 0.9.0
 ### Changed
 - Address conversion to string now defined for all inputs.
diff --git a/haskoin-core.cabal b/haskoin-core.cabal
--- a/haskoin-core.cabal
+++ b/haskoin-core.cabal
@@ -4,10 +4,10 @@
 --
 -- see: https://github.com/sol/hpack
 --
--- hash: 88ebd4a51caa718564de69955c74a49d2279bc2d1fe883c83ae035f529168813
+-- hash: 571964654e85fdc471bd843a2c43a1debee35c14aca24a8cdba815efd5c09736
 
 name:           haskoin-core
-version:        0.9.0
+version:        0.9.1
 synopsis:       Bitcoin & Bitcoin Cash library for Haskell
 description:    Haskoin Core is a complete Bitcoin and Bitcoin Cash library of functions and data types for Haskell developers.
 category:       Bitcoin, Finance, Network
@@ -80,6 +80,7 @@
       Paths_haskoin_core
   hs-source-dirs:
       src
+  ghc-options: -O2
   build-depends:
       QuickCheck
     , aeson
diff --git a/src/Network/Haskoin/Transaction/Builder.hs b/src/Network/Haskoin/Transaction/Builder.hs
--- a/src/Network/Haskoin/Transaction/Builder.hs
+++ b/src/Network/Haskoin/Transaction/Builder.hs
@@ -20,6 +20,7 @@
     , buildInput
     , SigInput(..)
     , signTx
+    , makeSignature
     , signInput
     , verifyStdTx
     , mergeTxs
@@ -275,7 +276,7 @@
     , sigInputValue  :: !Word64       -- ^ output script value
     , sigInputOP     :: !OutPoint     -- ^ outpoint to spend
     , sigInputSH     :: !SigHash      -- ^ signature type
-    , sigInputRedeem :: !(Maybe RedeemScript) -- ^ sedeem script
+    , sigInputRedeem :: !(Maybe RedeemScript) -- ^ redeem script
     } deriving (Eq, Show, Read, Generic, Hashable)
 
 instance ToJSON SigInput where
@@ -313,16 +314,22 @@
         keys <- sigKeys so rdmM allKeys
         foldM (\t k -> signInput net t i sigi k) tx keys
 
+-- | Produce a structured representation of a deterministic (RFC-6979) signature over an input.
+makeSignature :: Network -> Tx -> Int -> SigInput -> SecKeyI -> TxSignature
+makeSignature net tx i (SigInput so val _ sh rdmM) key =
+    TxSignature (signHash (secKeyData key) m) sh
+  where
+    m = txSigHash net tx (encodeOutput $ fromMaybe so rdmM) val i sh
+
 -- | Sign a single input in a transaction deterministically (RFC-6979).
 signInput :: Network -> Tx -> Int -> SigInput -> SecKeyI -> Either String Tx
-signInput net tx i (SigInput so val _ sh rdmM) key = do
-    let sig = TxSignature (signHash (secKeyData key) m) sh
+signInput net tx i sigIn@(SigInput so val _ sh rdmM) key = do
+    let sig = makeSignature net tx i sigIn key
     si <- buildInput net tx i so val rdmM sig $ derivePubKeyI key
     let ins = updateIndex i (txIn tx) (f si)
     return $ Tx (txVersion tx) ins (txOut tx) [] (txLockTime tx)
   where
     f si x = x {scriptInput = encodeInputBS si}
-    m = txSigHash net tx (encodeOutput $ fromMaybe so rdmM) val i sh
 
 -- | Order the 'SigInput' with respect to the transaction inputs. This allows
 -- the user to provide the 'SigInput' in any order. Users can also provide only