diff --git a/.changes/20261023_sub_transaction_witness_assemble.yml b/.changes/20261023_sub_transaction_witness_assemble.yml
new file mode 100644
index 0000000000..ca136bc091
--- /dev/null
+++ b/.changes/20261023_sub_transaction_witness_assemble.yml
@@ -0,0 +1,5 @@
+project: cardano-cli
+pr: 1485
+kind:
+  - feature
+description: Add Dijkstra sub-transaction witness and assemble commands to create key witnesses separately and combine them with an unsigned sub-transaction.
diff --git a/cardano-cli/src/Cardano/CLI/EraBased/Transaction/SubTransaction/Command.hs b/cardano-cli/src/Cardano/CLI/EraBased/Transaction/SubTransaction/Command.hs
index c8cc7721d4..fe6f5c037f 100644
--- a/cardano-cli/src/Cardano/CLI/EraBased/Transaction/SubTransaction/Command.hs
+++ b/cardano-cli/src/Cardano/CLI/EraBased/Transaction/SubTransaction/Command.hs
@@ -6,6 +6,8 @@ module Cardano.CLI.EraBased.Transaction.SubTransaction.Command
   ( SubTransactionCmds (..)
   , SubTransactionBuildRawCmdArgs (..)
   , SubTransactionSignCmdArgs (..)
+  , SubTransactionWitnessCmdArgs (..)
+  , SubTransactionAssembleCmdArgs (..)
   , SubTransactionTxIdCmdArgs (..)
   , Guard (..)
   , GuardScript (..)
@@ -30,6 +32,8 @@ import Vary (Vary)
 data SubTransactionCmds
   = SubTransactionBuildRawCmd !SubTransactionBuildRawCmdArgs
   | SubTransactionSignCmd !SubTransactionSignCmdArgs
+  | SubTransactionWitnessCmd !SubTransactionWitnessCmdArgs
+  | SubTransactionAssembleCmd !SubTransactionAssembleCmdArgs
   | SubTransactionTxIdCmd !SubTransactionTxIdCmdArgs
 
 -- | Like 'TransactionBuildRawCmdArgs' for a sub-transaction body. A
@@ -95,6 +99,20 @@ data SubTransactionSignCmdArgs = SubTransactionSignCmdArgs
   }
   deriving Show
 
+data SubTransactionWitnessCmdArgs = SubTransactionWitnessCmdArgs
+  { subTxFile :: !(UnsignedSubTxFile In)
+  , witnessSigningData :: !WitnessSigningData
+  , outFile :: !(File () Out)
+  }
+  deriving Show
+
+data SubTransactionAssembleCmdArgs = SubTransactionAssembleCmdArgs
+  { subTxFile :: !(UnsignedSubTxFile In)
+  , witnessFiles :: ![WitnessFile]
+  , outFile :: !(SignedSubTxFile Out)
+  }
+  deriving Show
+
 data SubTransactionTxIdCmdArgs = SubTransactionTxIdCmdArgs
   { inputSubTxFile :: !InputSubTxFile
   , outputFormat :: !(Vary [FormatJson, FormatText, FormatYaml])
@@ -105,4 +123,6 @@ renderSubTransactionCmds :: SubTransactionCmds -> Text
 renderSubTransactionCmds = \case
   SubTransactionBuildRawCmd{} -> "sub-transaction build-raw"
   SubTransactionSignCmd{} -> "sub-transaction sign"
+  SubTransactionWitnessCmd{} -> "sub-transaction witness"
+  SubTransactionAssembleCmd{} -> "sub-transaction assemble"
   SubTransactionTxIdCmd{} -> "sub-transaction txid"
diff --git a/cardano-cli/src/Cardano/CLI/EraBased/Transaction/SubTransaction/Option.hs b/cardano-cli/src/Cardano/CLI/EraBased/Transaction/SubTransaction/Option.hs
index 349aecff64..35b9f6ff10 100644
--- a/cardano-cli/src/Cardano/CLI/EraBased/Transaction/SubTransaction/Option.hs
+++ b/cardano-cli/src/Cardano/CLI/EraBased/Transaction/SubTransaction/Option.hs
@@ -73,6 +73,16 @@ pSubTransactionCmds =
               commandWithMetavar "sign" $
                 Opt.info pSubTransactionSign $
                   Opt.progDesc "Sign a sub-transaction"
+        , Just $
+            Opt.hsubparser $
+              commandWithMetavar "witness" $
+                Opt.info pSubTransactionWitness $
+                  Opt.progDesc "Create a sub-transaction key witness"
+        , Just $
+            Opt.hsubparser $
+              commandWithMetavar "assemble" $
+                Opt.info pSubTransactionAssemble $
+                  Opt.progDesc "Assemble an unsigned sub-transaction and key witnesses into a signed sub-transaction"
         , Just $
             Opt.hsubparser $
               commandWithMetavar "txid" $
@@ -144,6 +154,22 @@ pSubTransactionSign =
       <*> many pSubTransactionSigningData
       <*> pSignedSubTxFileOut
 
+pSubTransactionWitness :: Parser SubTransactionCmds
+pSubTransactionWitness =
+  fmap SubTransactionWitnessCmd $
+    SubTransactionWitnessCmdArgs
+      <$> pUnsignedSubTxFileIn
+      <*> pSubTransactionSigningData
+      <*> pOutputFile
+
+pSubTransactionAssemble :: Parser SubTransactionCmds
+pSubTransactionAssemble =
+  fmap SubTransactionAssembleCmd $
+    SubTransactionAssembleCmdArgs
+      <$> pUnsignedSubTxFileIn
+      <*> many pWitnessFile
+      <*> pSignedSubTxFileOut
+
 pSubTransactionTxId :: Parser SubTransactionCmds
 pSubTransactionTxId =
   fmap SubTransactionTxIdCmd $
diff --git a/cardano-cli/src/Cardano/CLI/EraBased/Transaction/SubTransaction/Run.hs b/cardano-cli/src/Cardano/CLI/EraBased/Transaction/SubTransaction/Run.hs
index b28af3cf30..e665942bfa 100644
--- a/cardano-cli/src/Cardano/CLI/EraBased/Transaction/SubTransaction/Run.hs
+++ b/cardano-cli/src/Cardano/CLI/EraBased/Transaction/SubTransaction/Run.hs
@@ -15,6 +15,8 @@ module Cardano.CLI.EraBased.Transaction.SubTransaction.Run
   ( runSubTransactionCmds
   , runSubTransactionBuildRawCmd
   , runSubTransactionSignCmd
+  , runSubTransactionWitnessCmd
+  , runSubTransactionAssembleCmd
   , runSubTransactionTxIdCmd
   , readSignedSubTransactions
   , validateCanonicalSubTransactions
@@ -69,6 +71,8 @@ runSubTransactionCmds :: Cmd.SubTransactionCmds -> CIO e ()
 runSubTransactionCmds = \case
   Cmd.SubTransactionBuildRawCmd args -> runSubTransactionBuildRawCmd args
   Cmd.SubTransactionSignCmd args -> runSubTransactionSignCmd args
+  Cmd.SubTransactionWitnessCmd args -> runSubTransactionWitnessCmd args
+  Cmd.SubTransactionAssembleCmd args -> runSubTransactionAssembleCmd args
   Cmd.SubTransactionTxIdCmd args -> runSubTransactionTxIdCmd args
 
 -- | Read the signed sub-transactions named on the command line, checking that
@@ -479,6 +483,56 @@ runSubTransactionSignCmd
 
     fromEitherIOCli $ writeFileTextEnvelope outFile Nothing signed
 
+runSubTransactionWitnessCmd
+  :: Cmd.SubTransactionWitnessCmdArgs
+  -> CIO e ()
+runSubTransactionWitnessCmd
+  Cmd.SubTransactionWitnessCmdArgs
+    { subTxFile = File subTxFilePath
+    , witnessSigningData
+    , outFile
+    } = do
+    subTxFile <- liftIO $ fileOrPipe subTxFilePath
+    unsigned <-
+      fromEitherIOCli $ first TxCmdTextEnvError <$> readFileUnsignedSubTx subTxFile
+    signingWitness <-
+      fromEitherIOCli $
+        first TxCmdReadWitnessSigningDataError <$> readWitnessSigningData witnessSigningData
+    key <- case categoriseSomeSigningWitness signingWitness of
+      AByronWitness _ -> throwCliError TxCmdSubTxByronWitnessUnsupported
+      AShelleyKeyWitness key -> pure key
+    let witness = ShelleyKeyWitness ShelleyBasedEraDijkstra $ Exp.makeSubTxKeyWitness unsigned key
+    fromEitherIOCli $
+      first TxCmdWriteFileError <$> writeTxWitnessFileTextEnvelope ShelleyBasedEraDijkstra outFile witness
+
+runSubTransactionAssembleCmd
+  :: Cmd.SubTransactionAssembleCmdArgs
+  -> CIO e ()
+runSubTransactionAssembleCmd
+  Cmd.SubTransactionAssembleCmdArgs
+    { subTxFile = File subTxFilePath
+    , witnessFiles
+    , outFile
+    } = do
+    subTxFile <- liftIO $ fileOrPipe subTxFilePath
+    unsigned <-
+      fromEitherIOCli $ first TxCmdTextEnvError <$> readFileUnsignedSubTx subTxFile
+    keyWits <- forM witnessFiles $ \witnessFile@(WitnessFile path) -> do
+      InAnyShelleyBasedEra era witness <-
+        fromEitherIOCli $ first TxCmdTextEnvError <$> readFileTxKeyWitness path
+      case era of
+        ShelleyBasedEraDijkstra -> case witness of
+          ShelleyKeyWitness _ keyWit -> pure keyWit
+          ShelleyBootstrapWitness{} -> throwCliError TxCmdSubTxByronWitnessUnsupported
+        _ ->
+          throwCliError $
+            TxCmdWitnessEraMismatch
+              (AnyCardanoEra DijkstraEra)
+              (AnyCardanoEra $ toCardanoEra era)
+              witnessFile
+    -- Preserve the body bytes covered by the signatures, as in 'sign'.
+    fromEitherIOCli $ writeFileTextEnvelope outFile Nothing $ Exp.signSubTx [] keyWits unsigned
+
 runSubTransactionTxIdCmd
   :: Cmd.SubTransactionTxIdCmdArgs
   -> CIO e ()
diff --git a/cardano-cli/test/cardano-cli-golden/Test/Golden/Dijkstra/Transaction/SubTransaction.hs b/cardano-cli/test/cardano-cli-golden/Test/Golden/Dijkstra/Transaction/SubTransaction.hs
index 4481913fc2..70fb37725d 100644
--- a/cardano-cli/test/cardano-cli-golden/Test/Golden/Dijkstra/Transaction/SubTransaction.hs
+++ b/cardano-cli/test/cardano-cli-golden/Test/Golden/Dijkstra/Transaction/SubTransaction.hs
@@ -60,6 +60,35 @@ hprop_golden_dijkstra_transaction_sub_transaction_pipeline =
         ]
     H.diffFileVsGoldenFile signedSubTxFile (goldenDir <> "/signed_out")
 
+    -- Creating a detached witness and assembling must reproduce direct signing.
+    witnessFile <- noteTempFile tempDir "sub-tx.witness"
+    void $
+      execCardanoCLI
+        [ "dijkstra"
+        , "sub-transaction"
+        , "witness"
+        , "--sub-tx-file"
+        , unsignedSubTxFile
+        , "--signing-key-file"
+        , signingKeyFile
+        , "--out-file"
+        , witnessFile
+        ]
+    H.diffFileVsGoldenFile witnessFile (goldenDir <> "/witness_out")
+    void $
+      execCardanoCLI
+        [ "dijkstra"
+        , "sub-transaction"
+        , "assemble"
+        , "--sub-tx-file"
+        , unsignedSubTxFile
+        , "--witness-file"
+        , witnessFile
+        , "--out-file"
+        , signedSubTxFile
+        ]
+    H.diffFileVsGoldenFile signedSubTxFile (goldenDir <> "/signed_out")
+
     -- The id is the body hash, so signing must not change it
     unsignedId <-
       execCardanoCLI
diff --git a/cardano-cli/test/cardano-cli-golden/files/golden/dijkstra/transaction/sub-transaction/witness_out b/cardano-cli/test/cardano-cli-golden/files/golden/dijkstra/transaction/sub-transaction/witness_out
new file mode 100644
index 0000000000..b3729ad395
--- /dev/null
+++ b/cardano-cli/test/cardano-cli-golden/files/golden/dijkstra/transaction/sub-transaction/witness_out
@@ -0,0 +1,5 @@
+{
+    "type": "TxWitness DijkstraEra",
+    "description": "Key Witness ShelleyEra",
+    "cborHex": "82582048d968a47923d491cbba6548e61cc3e347e658d1818d7bea90cf7d04ca13dbd15840449d80212dc4f45426f668daefe5dc22f60ff15c74b7262ccaebd8fad59504e05e19b03616a3305dcb4d0e384385b8bf7da7d059bfa112ad899223c7d1c6d400"
+}
diff --git a/cardano-cli/test/cardano-cli-golden/files/golden/help.cli b/cardano-cli/test/cardano-cli-golden/files/golden/help.cli
index 429eafe95d..b1f68c7e9c 100644
--- a/cardano-cli/test/cardano-cli-golden/files/golden/help.cli
+++ b/cardano-cli/test/cardano-cli-golden/files/golden/help.cli
@@ -5261,7 +5261,14 @@ Usage: cardano-cli dijkstra stake-pool metadata-hash
   Calculate the hash of a stake pool metadata file, optionally checking the
   obtained hash against an expected value.
 
-Usage: cardano-cli dijkstra sub-transaction (build-raw | sign | txid) 
+Usage: cardano-cli dijkstra sub-transaction 
+                                              ( build-raw
+                                              | sign
+                                              | witness
+                                              | assemble
+                                              | txid
+                                              )
+                                              
 
   Sub-transaction commands. A sub-transaction is built and signed on its own,
   then embedded in a top-level transaction.
@@ -5444,6 +5451,21 @@ Usage: cardano-cli dijkstra sub-transaction sign --sub-tx-file FILEPATH
 
   Sign a sub-transaction
 
+Usage: cardano-cli dijkstra sub-transaction witness --sub-tx-file FILEPATH
+                                                      --signing-key-file FILEPATH
+                                                      --out-file FILEPATH
+                                                      
+
+  Create a sub-transaction key witness
+
+Usage: cardano-cli dijkstra sub-transaction assemble --sub-tx-file FILEPATH
+                                                       [--witness-file FILEPATH]
+                                                       --out-file FILEPATH
+                                                       
+
+  Assemble an unsigned sub-transaction and key witnesses into a signed
+  sub-transaction
+
 Usage: cardano-cli dijkstra sub-transaction txid 
                                                    ( --sub-tx-file FILEPATH
                                                    | --signed-sub-tx-file FILEPATH
diff --git a/cardano-cli/test/cardano-cli-golden/files/golden/help/dijkstra_sub-transaction.cli b/cardano-cli/test/cardano-cli-golden/files/golden/help/dijkstra_sub-transaction.cli
index 2576cebec8..44fce59213 100644
--- a/cardano-cli/test/cardano-cli-golden/files/golden/help/dijkstra_sub-transaction.cli
+++ b/cardano-cli/test/cardano-cli-golden/files/golden/help/dijkstra_sub-transaction.cli
@@ -1,4 +1,11 @@
-Usage: cardano-cli dijkstra sub-transaction (build-raw | sign | txid) 
+Usage: cardano-cli dijkstra sub-transaction 
+                                              ( build-raw
+                                              | sign
+                                              | witness
+                                              | assemble
+                                              | txid
+                                              )
+                                              
 
   Sub-transaction commands. A sub-transaction is built and signed on its own,
   then embedded in a top-level transaction.
@@ -12,4 +19,7 @@ Available commands:
 
                            Please note the order[93;22;23;24m of some cmd options is crucial. If used incorrectly may produce undesired sub-transaction body. See nested [] notation above for details.[0;22;23;24m
   sign                     Sign a sub-transaction
+  witness                  Create a sub-transaction key witness
+  assemble                 Assemble an unsigned sub-transaction and key
+                           witnesses into a signed sub-transaction
   txid                     Print a sub-transaction identifier.
diff --git a/cardano-cli/test/cardano-cli-golden/files/golden/help/dijkstra_sub-transaction_assemble.cli b/cardano-cli/test/cardano-cli-golden/files/golden/help/dijkstra_sub-transaction_assemble.cli
new file mode 100644
index 0000000000..154492abc1
--- /dev/null
+++ b/cardano-cli/test/cardano-cli-golden/files/golden/help/dijkstra_sub-transaction_assemble.cli
@@ -0,0 +1,13 @@
+Usage: cardano-cli dijkstra sub-transaction assemble --sub-tx-file FILEPATH
+                                                       [--witness-file FILEPATH]
+                                                       --out-file FILEPATH
+                                                       
+
+  Assemble an unsigned sub-transaction and key witnesses into a signed
+  sub-transaction
+
+Available options:
+  --sub-tx-file FILEPATH   Input filepath of the JSON unsigned sub-transaction.
+  --witness-file FILEPATH  Filepath of the witness
+  --out-file FILEPATH      Output filepath of the JSON signed sub-transaction.
+  -h,--help                Show this help text
diff --git a/cardano-cli/test/cardano-cli-golden/files/golden/help/dijkstra_sub-transaction_witness.cli b/cardano-cli/test/cardano-cli-golden/files/golden/help/dijkstra_sub-transaction_witness.cli
new file mode 100644
index 0000000000..a33de9c575
--- /dev/null
+++ b/cardano-cli/test/cardano-cli-golden/files/golden/help/dijkstra_sub-transaction_witness.cli
@@ -0,0 +1,13 @@
+Usage: cardano-cli dijkstra sub-transaction witness --sub-tx-file FILEPATH
+                                                      --signing-key-file FILEPATH
+                                                      --out-file FILEPATH
+                                                      
+
+  Create a sub-transaction key witness
+
+Available options:
+  --sub-tx-file FILEPATH   Input filepath of the JSON unsigned sub-transaction.
+  --signing-key-file FILEPATH
+                           Input filepath of the signing key.
+  --out-file FILEPATH      The output file.
+  -h,--help                Show this help text
diff --git a/cardano-cli/test/cardano-cli-test/Test/Cli/Transaction/SubTransaction.hs b/cardano-cli/test/cardano-cli-test/Test/Cli/Transaction/SubTransaction.hs
index 7f9ee8ac0c..2cf9f58dc0 100644
--- a/cardano-cli/test/cardano-cli-test/Test/Cli/Transaction/SubTransaction.hs
+++ b/cardano-cli/test/cardano-cli-test/Test/Cli/Transaction/SubTransaction.hs
@@ -43,15 +43,168 @@ txIn = "63e6a9a8e58e48cc025cae04daaed9d36fc7b70bc292721d9f5057ae37b24981#0"
 txOut :: String
 txOut = "addr_test1vp0t4dfa9ktc2uvv7sg9leafuhtwyu0xcj4q4kf5pqkpjwqhklklg+5000000"
 
+-- | Detached signing preserves every payload and agrees with direct signing,
+-- including empty witness sets, multiple key roles and duplicate witnesses.
+hprop_dijkstra_sub_transaction_witness_assemble :: Property
+hprop_dijkstra_sub_transaction_witness_assemble =
+  watchdogProp . propertyOnce $ H.moduleWorkspace "tmp" $ \tempDir -> do
+    unsignedFile <- H.noteTempFile tempDir "sub.unsigned"
+    signedFile <- H.noteTempFile tempDir "sub.signed"
+    assembledFile <- H.noteTempFile tempDir "sub.assembled"
+    paramsFile <- H.noteTempFile tempDir "params.json"
+    metadataFile <- H.noteTempFile tempDir "metadata.json"
+    stakeKeyFile <- H.noteTempFile tempDir "stake.skey"
+    stakeVKeyFile <- H.noteTempFile tempDir "stake.vkey"
+    H.evalIO $ writeDijkstraProtocolParams paramsFile
+    H.evalIO $ writeFile metadataFile "{\"0\":42}"
+    void $
+      execCardanoCLI
+        [ "dijkstra"
+        , "stake-address"
+        , "key-gen"
+        , "--signing-key-file"
+        , stakeKeyFile
+        , "--verification-key-file"
+        , stakeVKeyFile
+        ]
+    forM_ [False, True] $ \canonical -> do
+      void $
+        execCardanoCLI $
+          subTransactionArgs
+            ++ [ "--tx-in-script-file"
+               , plutusScriptFile 4
+               , "--tx-in-datum-value"
+               , "0"
+               , "--tx-in-redeemer-value"
+               , "0"
+               , "--tx-in-execution-units"
+               , "(0,0)"
+               , "--guard-script-file"
+               , nativeScriptFile
+               , "--metadata-json-file"
+               , metadataFile
+               , "--protocol-params-file"
+               , paramsFile
+               , "--out-file"
+               , unsignedFile
+               ]
+            ++ concat (replicate 24 ["--tx-out", txOut])
+            ++ ["--out-canonical-cbor" | canonical]
+      unsigned@(Exp.UnsignedSubTx unsignedTx) <-
+        H.evalEither =<< H.evalIO (readFileTextEnvelope (File unsignedFile))
+      let bodyBytes = L.originalBytes (unsignedTx ^. L.bodyTxL)
+      canonicalBytes <- H.evalEither $ canonicaliseCborBs bodyBytes
+      (bodyBytes == canonicalBytes) H.=== canonical
+      witnesses <- forM (zip ["payment", "stake"] [signingKey, stakeKeyFile]) $ \(name, key) -> do
+        witnessFile <- H.noteTempFile tempDir (name ++ ".witness")
+        void $
+          execCardanoCLI
+            [ "dijkstra"
+            , "sub-transaction"
+            , "witness"
+            , "--sub-tx-file"
+            , unsignedFile
+            , "--signing-key-file"
+            , key
+            , "--out-file"
+            , witnessFile
+            ]
+        pure witnessFile
+      forM_ [0, 1, 2, 3] $ \count -> do
+        let keys = take count [signingKey, stakeKeyFile, signingKey]
+            files = take count (witnesses ++ witnesses)
+        void $
+          execCardanoCLI $
+            ["dijkstra", "sub-transaction", "sign", "--sub-tx-file", unsignedFile, "--out-file", signedFile]
+              ++ concatMap (\key -> ["--signing-key-file", key]) keys
+        void $
+          execCardanoCLI $
+            [ "dijkstra"
+            , "sub-transaction"
+            , "assemble"
+            , "--sub-tx-file"
+            , unsignedFile
+            , "--out-file"
+            , assembledFile
+            ]
+              ++ concatMap (\file -> ["--witness-file", file]) files
+        signedBytes <- H.evalIO $ BS.readFile signedFile
+        assembledBytes <- H.evalIO $ BS.readFile assembledFile
+        assembledBytes H.=== signedBytes
+        assembled@(Exp.SignedSubTx assembledTx) <-
+          H.evalEither =<< H.evalIO (readFileTextEnvelope (File assembledFile))
+        Exp.getSignedSubTxId assembled H.=== Exp.getUnsignedSubTxId unsigned
+        L.originalBytes (assembledTx ^. L.bodyTxL) H.=== bodyBytes
+        assembledTx ^. L.auxDataTxL H.=== unsignedTx ^. L.auxDataTxL
+        assembledTx ^. L.witsTxL . L.scriptTxWitsL H.=== unsignedTx ^. L.witsTxL . L.scriptTxWitsL
+        assembledTx ^. L.witsTxL . L.datsTxWitsL H.=== unsignedTx ^. L.witsTxL . L.datsTxWitsL
+        assembledTx ^. L.witsTxL . L.rdmrsTxWitsL H.=== unsignedTx ^. L.witsTxL . L.rdmrsTxWitsL
+        Set.size (assembledTx ^. L.witsTxL . L.addrTxWitsL) H.=== min count 2
+
+-- | Bad inputs fail before creating output; assembly accepts only Dijkstra witnesses.
+hprop_dijkstra_sub_transaction_witness_assemble_rejects_invalid_inputs :: Property
+hprop_dijkstra_sub_transaction_witness_assemble_rejects_invalid_inputs =
+  watchdogProp . propertyOnce $ H.moduleWorkspace "tmp" $ \tempDir -> do
+    unsignedFile <- H.noteTempFile tempDir "sub.unsigned"
+    signedFile <- H.noteTempFile tempDir "sub.signed"
+    malformedFile <- H.noteTempFile tempDir "malformed.json"
+    missingFile <- H.noteTempFile tempDir "missing.json"
+    bodyFile <- H.noteTempFile tempDir "conway.body"
+    witnessFile <- H.noteTempFile tempDir "conway.witness"
+    outFile <- H.noteTempFile tempDir "output"
+    H.evalIO $ writeFile malformedFile "{}"
+    void $ execCardanoCLI $ subTransactionArgs ++ ["--out-file", unsignedFile]
+    void $
+      execCardanoCLI
+        ["dijkstra", "sub-transaction", "sign", "--sub-tx-file", unsignedFile, "--out-file", signedFile]
+    void $
+      execCardanoCLI
+        ["conway", "transaction", "build-raw", "--tx-in", txIn, "--fee", "0", "--out-file", bodyFile]
+    void $
+      execCardanoCLI
+        [ "conway"
+        , "transaction"
+        , "witness"
+        , "--tx-body-file"
+        , bodyFile
+        , "--signing-key-file"
+        , signingKey
+        , "--out-file"
+        , witnessFile
+        ]
+    let reject command args = do
+          (exitCode, _, stderr) <-
+            execDetailCardanoCLI $ ["dijkstra", "sub-transaction", command] ++ args ++ ["--out-file", outFile]
+          exitCode H.=== ExitFailure 1
+          H.evalIO (doesFileExist outFile) >>= (H.=== False)
+          pure stderr
+    stderr <- reject "assemble" ["--sub-tx-file", unsignedFile, "--witness-file", witnessFile]
+    H.assertWith stderr ("The era of a witness does not match" `isInfixOf`)
+    forM_ [signedFile, malformedFile, missingFile] $ \input -> do
+      void $ reject "witness" ["--sub-tx-file", input, "--signing-key-file", signingKey]
+      void $ reject "assemble" ["--sub-tx-file", input]
+    forM_ [malformedFile, missingFile] $ \input -> do
+      void $ reject "witness" ["--sub-tx-file", unsignedFile, "--signing-key-file", input]
+      void $ reject "assemble" ["--sub-tx-file", unsignedFile, "--witness-file", input]
+    void $ reject "witness" ["--sub-tx-file", unsignedFile]
+    void $
+      reject
+        "witness"
+        ["--sub-tx-file", unsignedFile, "--signing-key-file", signingKey, "--signing-key-file", signingKey]
+    forM_ ["witness", "assemble"] $ \command -> do
+      (exitCode, _, conwayError) <- execDetailCardanoCLI ["conway", "sub-transaction", command]
+      exitCode H.=== ExitFailure 1
+      H.assertWith conwayError ("Invalid argument `sub-transaction'" `isInfixOf`)
+
 -- | Sub-transaction signing rejects the Byron-only address option at parse time.
 hprop_dijkstra_sub_transaction_sign_rejects_address :: Property
 hprop_dijkstra_sub_transaction_sign_rejects_address =
-  watchdogProp . propertyOnce $ do
+  watchdogProp . propertyOnce $ forM_ ["sign", "witness"] $ \command -> do
     (exitCode, _, stderr) <-
       execDetailCardanoCLI
         [ "dijkstra"
         , "sub-transaction"
-        , "sign"
+        , command
         , "--sub-tx-file"
         , "unused"
         , "--signing-key-file"
@@ -260,12 +413,12 @@ hprop_dijkstra_sub_transaction_sign_rejects_byron_key =
         , "--out-file"
         , byronKeyFile
         ]
-    (exitCode, _stdout, stderr) <-
-      H.noteShowM $
+    forM_ ["sign", "witness"] $ \command -> do
+      (exitCode, _, stderr) <-
         execDetailCardanoCLI
           [ "dijkstra"
           , "sub-transaction"
-          , "sign"
+          , command
           , "--sub-tx-file"
           , unsignedFile
           , "--signing-key-file"
@@ -273,10 +426,48 @@ hprop_dijkstra_sub_transaction_sign_rejects_byron_key =
           , "--out-file"
           , outFile
           ]
+      exitCode H.=== ExitFailure 1
+      H.assertWith
+        stderr
+        ("Byron (bootstrap) witnesses are not supported for sub-transactions" `isInfixOf`)
+      H.evalIO (doesFileExist outFile) >>= (H.=== False)
+    -- A correctly encoded Dijkstra bootstrap witness must also be refused.
+    bodyFile <- H.noteTempFile tempDir "tx.body"
+    witnessFile <- H.noteTempFile tempDir "byron.witness"
+    void $
+      execCardanoCLI
+        ["dijkstra", "transaction", "build-raw", "--tx-in", txIn, "--fee", "0", "--out-file", bodyFile]
+    void $
+      execCardanoCLI
+        [ "dijkstra"
+        , "transaction"
+        , "witness"
+        , "--tx-body-file"
+        , bodyFile
+        , "--signing-key-file"
+        , byronKeyFile
+        , "--testnet-magic"
+        , "42"
+        , "--out-file"
+        , witnessFile
+        ]
+    (exitCode, _, stderr) <-
+      execDetailCardanoCLI
+        [ "dijkstra"
+        , "sub-transaction"
+        , "assemble"
+        , "--sub-tx-file"
+        , unsignedFile
+        , "--witness-file"
+        , witnessFile
+        , "--out-file"
+        , outFile
+        ]
     exitCode H.=== ExitFailure 1
     H.assertWith
       stderr
       ("Byron (bootstrap) witnesses are not supported for sub-transactions" `isInfixOf`)
+    H.evalIO (doesFileExist outFile) >>= (H.=== False)
 
 -- | A large output list uses indefinite-length CBOR by default. Canonicalising
 -- the batch must fail rather than invalidate the embedded signature.