diff --git a/external-sop/src/main/java/sop/external/operation/InlineDetachExternal.java b/external-sop/src/main/java/sop/external/operation/InlineDetachExternal.java
deleted file mode 100644
index a798006..0000000
--- a/external-sop/src/main/java/sop/external/operation/InlineDetachExternal.java
+++ /dev/null
@@ -1,106 +0,0 @@
-// SPDX-FileCopyrightText: 2023 Paul Schaub <vanitasvitae@fsfe.org>
-//
-// SPDX-License-Identifier: Apache-2.0
-
-package sop.external.operation;
-
-import sop.ReadyWithResult;
-import sop.Signatures;
-import sop.exception.SOPGPException;
-import sop.external.ExternalSOP;
-import sop.operation.InlineDetach;
-
-import javax.annotation.Nonnull;
-import java.io.ByteArrayOutputStream;
-import java.io.File;
-import java.io.FileInputStream;
-import java.io.IOException;
-import java.io.InputStream;
-import java.io.OutputStream;
-import java.util.ArrayList;
-import java.util.List;
-import java.util.Properties;
-
-/**
- * Implementation of the {@link InlineDetach} operation using an external SOP binary.
- */
-public class InlineDetachExternal implements InlineDetach {
-
-    private final ExternalSOP.TempDirProvider tempDirProvider;
-    private final List<String> commandList = new ArrayList<>();
-    private final List<String> envList;
-
-    public InlineDetachExternal(String binary, Properties environment, ExternalSOP.TempDirProvider tempDirProvider) {
-        this.tempDirProvider = tempDirProvider;
-        commandList.add(binary);
-        commandList.add("inline-detach");
-        envList = ExternalSOP.propertiesToEnv(environment);
-    }
-
-    @Override
-    @Nonnull
-    public InlineDetach noArmor() {
-        commandList.add("--no-armor");
-        return this;
-    }
-
-    @Override
-    @Nonnull
-    public ReadyWithResult<Signatures> message(@Nonnull InputStream messageInputStream) throws IOException, SOPGPException.BadData {
-        File tempDir = tempDirProvider.provideTempDirectory();
-
-        File signaturesOut = new File(tempDir, "signatures");
-        signaturesOut.delete();
-        commandList.add("--signatures-out=" + signaturesOut.getAbsolutePath());
-
-        String[] command = commandList.toArray(new String[0]);
-        String[] env = envList.toArray(new String[0]);
-
-        try {
-            Process process = Runtime.getRuntime().exec(command, env);
-            OutputStream processOut = process.getOutputStream();
-            InputStream processIn = process.getInputStream();
-
-            return new ReadyWithResult<Signatures>() {
-                @Override
-                public Signatures writeTo(@Nonnull OutputStream outputStream) throws IOException {
-                    byte[] buf = new byte[4096];
-                    int r;
-                    while ((r = messageInputStream.read(buf)) > 0) {
-                        processOut.write(buf, 0, r);
-                    }
-
-                    messageInputStream.close();
-                    processOut.close();
-
-                    while ((r = processIn.read(buf)) > 0) {
-                        outputStream.write(buf, 0 , r);
-                    }
-
-                    processIn.close();
-                    outputStream.close();
-
-                    ExternalSOP.finish(process);
-
-                    FileInputStream signaturesOutIn = new FileInputStream(signaturesOut);
-                    ByteArrayOutputStream signaturesBuffer = new ByteArrayOutputStream();
-                    while ((r = signaturesOutIn.read(buf)) > 0) {
-                        signaturesBuffer.write(buf, 0, r);
-                    }
-                    signaturesOutIn.close();
-                    signaturesOut.delete();
-
-                    final byte[] sigBytes = signaturesBuffer.toByteArray();
-                    return new Signatures() {
-                        @Override
-                        public void writeTo(@Nonnull OutputStream signatureOutputStream) throws IOException {
-                            signatureOutputStream.write(sigBytes);
-                        }
-                    };
-                }
-            };
-        } catch (IOException e) {
-            throw new RuntimeException(e);
-        }
-    }
-}
diff --git a/external-sop/src/main/kotlin/sop/external/operation/InlineDetachExternal.kt b/external-sop/src/main/kotlin/sop/external/operation/InlineDetachExternal.kt
new file mode 100644
index 0000000..f44e6bb
--- /dev/null
+++ b/external-sop/src/main/kotlin/sop/external/operation/InlineDetachExternal.kt
@@ -0,0 +1,82 @@
+// SPDX-FileCopyrightText: 2023 Paul Schaub <vanitasvitae@fsfe.org>
+//
+// SPDX-License-Identifier: Apache-2.0
+
+package sop.external.operation
+
+import java.io.*
+import java.util.*
+import sop.ReadyWithResult
+import sop.Signatures
+import sop.external.ExternalSOP
+import sop.external.ExternalSOP.Companion.finish
+import sop.operation.InlineDetach
+
+/** Implementation of the [InlineDetach] operation using an external SOP binary. */
+class InlineDetachExternal(
+    binary: String,
+    environment: Properties,
+    private val tempDirProvider: ExternalSOP.TempDirProvider
+) : InlineDetach {
+
+    private val commandList = mutableListOf(binary, "inline-detach")
+    private val envList = ExternalSOP.propertiesToEnv(environment)
+
+    override fun noArmor(): InlineDetach = apply { commandList.add("--no-armor") }
+
+    override fun message(messageInputStream: InputStream): ReadyWithResult<Signatures> {
+        val tempDir = tempDirProvider.provideTempDirectory()
+
+        val signaturesOut = File(tempDir, "signatures")
+        signaturesOut.delete()
+        commandList.add("--signatures-out=${signaturesOut.absolutePath}")
+
+        try {
+            val process =
+                Runtime.getRuntime().exec(commandList.toTypedArray(), envList.toTypedArray())
+            val processOut = process.outputStream
+            val processIn = process.inputStream
+
+            return object : ReadyWithResult<Signatures>() {
+                override fun writeTo(outputStream: OutputStream): Signatures {
+                    val buf = ByteArray(4096)
+                    var r: Int
+                    while (messageInputStream.read(buf).also { r = it } > 0) {
+                        processOut.write(buf, 0, r)
+                    }
+
+                    messageInputStream.close()
+                    processOut.close()
+
+                    while (processIn.read(buf).also { r = it } > 0) {
+                        outputStream.write(buf, 0, r)
+                    }
+
+                    processIn.close()
+                    outputStream.close()
+
+                    finish(process)
+
+                    val signaturesOutIn = FileInputStream(signaturesOut)
+                    val signaturesBuffer = ByteArrayOutputStream()
+                    while (signaturesOutIn.read(buf).also { r = it } > 0) {
+                        signaturesBuffer.write(buf, 0, r)
+                    }
+                    signaturesOutIn.close()
+                    signaturesOut.delete()
+
+                    val sigBytes = signaturesBuffer.toByteArray()
+
+                    return object : Signatures() {
+                        @Throws(IOException::class)
+                        override fun writeTo(outputStream: OutputStream) {
+                            outputStream.write(sigBytes)
+                        }
+                    }
+                }
+            }
+        } catch (e: IOException) {
+            throw RuntimeException(e)
+        }
+    }
+}