diff --git a/LICENSE b/LICENSE
new file mode 100644
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,24 @@
+Copyright (c) 2019, Stack contributors
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+    * Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+    * Redistributions in binary form must reproduce the above copyright
+      notice, this list of conditions and the following disclaimer in the
+      documentation and/or other materials provided with the distribution.
+    * Neither the name of Stack nor the
+      names of its contributors may be used to endorse or promote products
+      derived from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+DISCLAIMED. IN NO EVENT SHALL STACK CONTRIBUTORS BE LIABLE FOR ANY
+DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
diff --git a/casa-types.cabal b/casa-types.cabal
new file mode 100644
--- /dev/null
+++ b/casa-types.cabal
@@ -0,0 +1,30 @@
+cabal-version:  1.12
+synopsis:       Types for Casa
+description:    Types for Casa <https://casa.fpcomplete.com/>
+name:           casa-types
+copyright:      2018-2019 FP Complete
+author:         Chris Done
+maintainer:     chrisdone@fpcomplete.com
+license:        BSD3
+license-file:   LICENSE
+category: Development
+version:        0.0.0
+build-type:     Simple
+
+library
+  exposed-modules:
+    Casa.Types
+  other-modules: Paths_casa_types
+  hs-source-dirs: src
+  default-language: Haskell2010
+  ghc-options: -Wall
+  build-depends:
+       base >= 4.5 && < 4.7
+    , bytestring
+    , attoparsec
+    , base16-bytestring
+    , text
+    , hashable
+    , aeson
+    , path-pieces
+    , persistent
diff --git a/src/Casa/Types.hs b/src/Casa/Types.hs
new file mode 100644
--- /dev/null
+++ b/src/Casa/Types.hs
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+{-# LANGUAGE GeneralizedNewtypeDeriving #-}
+
+-- |
+
+module Casa.Types where
+
+import           Control.Monad
+import           Data.Aeson
+import qualified Data.Attoparsec.ByteString as Atto.B
+import qualified Data.Attoparsec.Text as Atto.T
+import           Data.ByteString (ByteString)
+import qualified Data.ByteString as S
+import qualified Data.ByteString.Base16 as Hex
+import qualified Data.ByteString.Builder as S
+import           Data.Hashable
+import           Database.Persist
+import           Database.Persist.Sql
+import           Data.Text (Text)
+import qualified Data.Text.Encoding as T
+import           Web.PathPieces
+
+-- | A SHA256 key to address blobs.
+newtype BlobKey =
+  BlobKey
+    { unBlobKey :: ByteString
+    }
+  deriving (Read, Eq, Ord, Hashable, PersistField, PersistFieldSql)
+
+instance Show BlobKey where
+  show (BlobKey key) = show (Hex.encode key)
+
+instance FromJSON BlobKey where
+  parseJSON = parseJSON >=> (either fail pure . blobKeyHexParser)
+
+instance ToJSON BlobKey where
+  toJSON = String . T.decodeUtf8 . Hex.encode . unBlobKey
+
+instance PathPiece BlobKey where
+  fromPathPiece =
+    either (const Nothing) Just .
+    blobKeyHexParser
+  toPathPiece = T.decodeUtf8 . Hex.encode . unBlobKey
+
+-- | Parse a blob key in hex format.
+blobKeyHexParser :: Text -> Either String BlobKey
+blobKeyHexParser =
+  Atto.T.parseOnly
+    (fmap
+       BlobKey
+       (do bytes <- Atto.T.take 64
+           case Hex.decode (T.encodeUtf8 bytes) of
+             (result, wrong) | S.null wrong -> pure result
+             _ -> fail "Invalid hex key."))
+
+-- | Parse a blob key in binary format.
+blobKeyBinaryParser :: Atto.B.Parser BlobKey
+blobKeyBinaryParser = fmap BlobKey (Atto.B.take 32)
+
+blobKeyToBuilder :: BlobKey -> S.Builder
+blobKeyToBuilder = S.byteString . unBlobKey