diff --git a/cabal.project b/cabal.project
new file mode 100644
index 0000000000000000000000000000000000000000..473de17fc163f47ae5bc06266af134a08889b4de
--- /dev/null
+++ b/cabal.project
@@ -0,0 +1,12 @@
+packages: .
+          -- These aren't released on hackage yet so we have to grab them
+          -- straight from the vcs host.  Probably should do some releases
+          -- soon.
+          https://whetstone.private.storage/privatestorage/tahoe-chk/-/archive/0.1.0.1/tahoe-chk-0.1.0.1.tar.gz
+
+package zlib
+        -- Turn on discovery of the underlying zlib using pkg-config.  This
+        -- fixes build failures when the underlying zlib is not in the
+        -- traditional location but is discoverable with pkg-config.  It might
+        -- break non-pkg-config platforms.
+        flags: +pkg-config
diff --git a/flake.lock b/flake.lock
index 16274dd6ca881162b90299c04d227defe60d2e14..ecb55129cd1ea483fafb1bc5d2965e08974b4d89 100644
--- a/flake.lock
+++ b/flake.lock
@@ -16,6 +16,22 @@
         "type": "github"
       }
     },
+    "flake-compat_2": {
+      "flake": false,
+      "locked": {
+        "lastModified": 1673956053,
+        "narHash": "sha256-4gtG9iQuiKITOjNQQeQIpoIB6b16fm+504Ch3sNKLd8=",
+        "owner": "edolstra",
+        "repo": "flake-compat",
+        "rev": "35bb57c0c8d8b62bbfd284272c928ceb64ddbde9",
+        "type": "github"
+      },
+      "original": {
+        "owner": "edolstra",
+        "repo": "flake-compat",
+        "type": "github"
+      }
+    },
     "flake-utils": {
       "inputs": {
         "systems": "systems"
@@ -49,6 +65,36 @@
         "type": "github"
       }
     },
+    "flake-utils_3": {
+      "locked": {
+        "lastModified": 1667395993,
+        "narHash": "sha256-nuEHfE/LcWyuSWnS8t12N1wc105Qtau+/OdUAjtQ0rA=",
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "rev": "5aed5285a952e0b949eb3ba02c12fa4fcfef535f",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "type": "github"
+      }
+    },
+    "flake-utils_4": {
+      "locked": {
+        "lastModified": 1676283394,
+        "narHash": "sha256-XX2f9c3iySLCw54rJ/CZs+ZK6IQy7GXNY4nSOyu2QG4=",
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "rev": "3db36a8b464d0c4532ba1c7dda728f4576d6d073",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "type": "github"
+      }
+    },
     "gitignore": {
       "inputs": {
         "nixpkgs": [
@@ -71,6 +117,29 @@
         "type": "github"
       }
     },
+    "gitignore_2": {
+      "inputs": {
+        "nixpkgs": [
+          "tahoe-chk",
+          "hs-flake-utils",
+          "pre-commit-hooks",
+          "nixpkgs"
+        ]
+      },
+      "locked": {
+        "lastModified": 1660459072,
+        "narHash": "sha256-8DFJjXG8zqoONA1vXtgeKXy68KdJL5UaXR8NtVMUbx8=",
+        "owner": "hercules-ci",
+        "repo": "gitignore.nix",
+        "rev": "a20de23b925fd8264fd7fad6454652e142fd7f73",
+        "type": "github"
+      },
+      "original": {
+        "owner": "hercules-ci",
+        "repo": "gitignore.nix",
+        "type": "github"
+      }
+    },
     "hs-flake-utils": {
       "inputs": {
         "flake-utils": "flake-utils_2",
@@ -92,6 +161,27 @@
         "url": "https://whetstone.private.storage/jcalderone/hs-flake-utils.git"
       }
     },
+    "hs-flake-utils_2": {
+      "inputs": {
+        "flake-utils": "flake-utils_4",
+        "nixpkgs": "nixpkgs_2",
+        "pre-commit-hooks": "pre-commit-hooks_2"
+      },
+      "locked": {
+        "lastModified": 1677773826,
+        "narHash": "sha256-xJmOtHugr4k2zNhP/AF6JdIUnIEyM+TEspLn2n5kloc=",
+        "ref": "main",
+        "rev": "d3a83fdd9563546ca41771186427638e685a2e2b",
+        "revCount": 9,
+        "type": "git",
+        "url": "https://whetstone.private.storage/jcalderone/hs-flake-utils.git"
+      },
+      "original": {
+        "ref": "main",
+        "type": "git",
+        "url": "https://whetstone.private.storage/jcalderone/hs-flake-utils.git"
+      }
+    },
     "nixpkgs": {
       "locked": {
         "lastModified": 1677624842,
@@ -124,6 +214,38 @@
         "type": "github"
       }
     },
+    "nixpkgs-stable_2": {
+      "locked": {
+        "lastModified": 1673800717,
+        "narHash": "sha256-SFHraUqLSu5cC6IxTprex/nTsI81ZQAtDvlBvGDWfnA=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "2f9fd351ec37f5d479556cd48be4ca340da59b8f",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixos-22.11",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "nixpkgs_2": {
+      "locked": {
+        "lastModified": 1677624842,
+        "narHash": "sha256-4DF9DbDuK4/+KYx0L6XcPBeDHUFVCtzok2fWtwXtb5w=",
+        "owner": "nixos",
+        "repo": "nixpkgs",
+        "rev": "d70f5cd5c3bef45f7f52698f39e7cc7a89daa7f0",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nixos",
+        "ref": "nixos-22.11",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
     "pre-commit-hooks": {
       "inputs": {
         "flake-compat": "flake-compat",
@@ -152,6 +274,36 @@
         "type": "github"
       }
     },
+    "pre-commit-hooks_2": {
+      "inputs": {
+        "flake-compat": "flake-compat_2",
+        "flake-utils": [
+          "tahoe-chk",
+          "hs-flake-utils",
+          "flake-utils"
+        ],
+        "gitignore": "gitignore_2",
+        "nixpkgs": [
+          "tahoe-chk",
+          "hs-flake-utils",
+          "nixpkgs"
+        ],
+        "nixpkgs-stable": "nixpkgs-stable_2"
+      },
+      "locked": {
+        "lastModified": 1677722096,
+        "narHash": "sha256-7mjVMvCs9InnrRybBfr5ohqcOz+pyEX8m22C1XsDilg=",
+        "owner": "cachix",
+        "repo": "pre-commit-hooks.nix",
+        "rev": "61a3511668891c68ebd19d40122150b98dc2fe3b",
+        "type": "github"
+      },
+      "original": {
+        "owner": "cachix",
+        "repo": "pre-commit-hooks.nix",
+        "type": "github"
+      }
+    },
     "root": {
       "inputs": {
         "flake-utils": "flake-utils",
@@ -159,7 +311,8 @@
         "nixpkgs": [
           "hs-flake-utils",
           "nixpkgs"
-        ]
+        ],
+        "tahoe-chk": "tahoe-chk"
       }
     },
     "systems": {
@@ -176,6 +329,30 @@
         "repo": "default",
         "type": "github"
       }
+    },
+    "tahoe-chk": {
+      "inputs": {
+        "flake-utils": "flake-utils_3",
+        "hs-flake-utils": "hs-flake-utils_2",
+        "nixpkgs": [
+          "hs-flake-utils",
+          "nixpkgs"
+        ]
+      },
+      "locked": {
+        "lastModified": 1683552888,
+        "narHash": "sha256-h9pgP/LYPtUr5CeCAhqt1XJyAqKTnkQxuIygiTulU/U=",
+        "ref": "refs/tags/0.1.0.1",
+        "rev": "05aeb5a433b85406ca3c0c313c46299a1026ade0",
+        "revCount": 344,
+        "type": "git",
+        "url": "https://whetstone.private.storage/PrivateStorage/tahoe-chk"
+      },
+      "original": {
+        "ref": "refs/tags/0.1.0.1",
+        "type": "git",
+        "url": "https://whetstone.private.storage/PrivateStorage/tahoe-chk"
+      }
     }
   },
   "root": "root",
diff --git a/flake.nix b/flake.nix
index 83f3d7f8f4685caa40ae4277c62bfc0530df7705..7b393e118ddd63bdf4f80c39c38fb8a07e3bc208 100644
--- a/flake.nix
+++ b/flake.nix
@@ -6,6 +6,10 @@
     flake-utils.url = github:numtide/flake-utils;
     hs-flake-utils.url = "git+https://whetstone.private.storage/jcalderone/hs-flake-utils.git?ref=main";
     nixpkgs.follows = "hs-flake-utils/nixpkgs";
+    tahoe-chk = {
+      url = "git+https://whetstone.private.storage/PrivateStorage/tahoe-chk?ref=refs/tags/0.1.0.1";
+      inputs.nixpkgs.follows = "hs-flake-utils/nixpkgs";
+    };
   };
 
   outputs = {
@@ -13,6 +17,7 @@
     nixpkgs,
     flake-utils,
     hs-flake-utils,
+    tahoe-chk,
   }: let
     ulib = flake-utils.lib;
     ghcVersion = "ghc8107";
@@ -27,6 +32,9 @@
         src = ./.;
         compilerVersion = ghcVersion;
         packageName = "tahoe-ssk";
+        hsPkgsOverrides = hprev: hfinal: {
+          tahoe-chk = tahoe-chk.outputs.packages.${system}.default;
+        };
       };
     in {
       checks = hslib.checks {};
diff --git a/src/Tahoe/SDMF.hs b/src/Tahoe/SDMF.hs
index 718741f435a403c5bd844e810d3f48a5fd6fcccb..0aaf41a1fa7e30ed6db779c836e1ce9da6a510fa 100644
--- a/src/Tahoe/SDMF.hs
+++ b/src/Tahoe/SDMF.hs
@@ -1 +1,4 @@
-module Tahoe.SDMF where
+-- | Expose the library's public interface.
+module Tahoe.SDMF (Share (..)) where
+
+import Tahoe.SDMF.Internal.Share
diff --git a/src/Tahoe/SDMF/Internal/Share.hs b/src/Tahoe/SDMF/Internal/Share.hs
new file mode 100644
index 0000000000000000000000000000000000000000..c31124dc3b6f980363dfda920d25359f1a85a4db
--- /dev/null
+++ b/src/Tahoe/SDMF/Internal/Share.hs
@@ -0,0 +1,34 @@
+-- | Deal with details related to the structural layout of an SDMF share.
+module Tahoe.SDMF.Internal.Share where
+
+import qualified Crypto.Types.PubKey.RSA as RSA
+import qualified Data.ByteString as B
+import qualified Data.ByteString.Lazy as LB
+import Data.Word (Word32, Word64, Word8)
+import Tahoe.CHK.Merkle (MerkleTree)
+
+{- | Structured representation of a single version 0 SDMF share.
+
+ See Tahoe-LAFS "mutable" specification document, section title "SDMF Slot
+ Format".
+-}
+data Share = Share
+    { shareSequenceNumber :: Word64
+    , shareRootHash :: B.ByteString
+    , shareIV :: B.ByteString
+    , shareTotalShares :: Word8
+    , shareRequiredShares :: Word8
+    , shareSegmentSize :: Word64
+    , shareDataLength :: Word8
+    , shareOffsetSignature :: Word32
+    , shareOffsetShareHashChain :: Word32
+    , shareOffsetData :: Word32
+    , shareOffsetEncryptedPrivateKey :: Word64
+    , shareOffsetEOF :: Word64
+    , shareVerificationKey :: RSA.PublicKey
+    , shareSignature :: B.ByteString
+    , shareHashChain :: [(Word8, B.ByteString)]
+    , shareBlockHashTree :: MerkleTree
+    , shareData :: LB.ByteString
+    , sharePrivateKey :: RSA.PrivateKey
+    }
diff --git a/tahoe-ssk.cabal b/tahoe-ssk.cabal
index 51ddf32a2dc759eb579b9360e60adcf74fe786ac..de3a3f9fefde9a164aa624ebb4ee77c437616260 100644
--- a/tahoe-ssk.cabal
+++ b/tahoe-ssk.cabal
@@ -61,11 +61,21 @@ common warnings
 
 library
   hs-source-dirs:     src
-  exposed-modules:    Tahoe.SDMF
-  build-depends:      base
+  exposed-modules:
+    Tahoe.SDMF
+    Tahoe.SDMF.Internal.Share
+
+  build-depends:
+    , base
+    , bytestring
+    , crypto-pubkey-types
+
+  -- This dependency isn't ideal.  Move common bits out to
+  -- another library.
+  build-depends:      tahoe-chk
   ghc-options:        -Wall
   default-extensions: OverloadedStrings
-  defaut-language:    Haskell2010
+  default-language:   Haskell2010
 
 test-suite tahoe-ssk-test
   -- Import common warning flags.
@@ -90,4 +100,6 @@ test-suite tahoe-ssk-test
   main-is:          Main.hs
 
   -- Test dependencies.
-  build-depends:    base ^>=4.14.3.0
+  build-depends:
+    , base       ^>=4.14.3.0
+    , tahoe-ssk