diff --git a/pgpainless-core/src/main/java/org/pgpainless/decryption_verification/DecryptionBuilder.java b/pgpainless-core/src/main/java/org/pgpainless/decryption_verification/DecryptionBuilder.java
deleted file mode 100644
index 96b4ad60..00000000
--- a/pgpainless-core/src/main/java/org/pgpainless/decryption_verification/DecryptionBuilder.java
+++ /dev/null
@@ -1,42 +0,0 @@
-// SPDX-FileCopyrightText: 2018 Paul Schaub <vanitasvitae@fsfe.org>
-//
-// SPDX-License-Identifier: Apache-2.0
-
-package org.pgpainless.decryption_verification;
-
-import java.io.IOException;
-import java.io.InputStream;
-import javax.annotation.Nonnull;
-
-import org.bouncycastle.openpgp.PGPException;
-
-/**
- * Builder class that takes an {@link InputStream} of ciphertext (or plaintext signed data)
- * and combines it with a configured {@link ConsumerOptions} object to form a {@link DecryptionStream} which
- * can be used to decrypt an OpenPGP message or verify signatures.
- */
-public class DecryptionBuilder implements DecryptionBuilderInterface {
-
-    @Override
-    public DecryptWith onInputStream(@Nonnull InputStream inputStream) {
-        return new DecryptWithImpl(inputStream);
-    }
-
-    static class DecryptWithImpl implements DecryptWith {
-
-        private final InputStream inputStream;
-
-        DecryptWithImpl(InputStream inputStream) {
-            this.inputStream = inputStream;
-        }
-
-        @Override
-        public DecryptionStream withOptions(ConsumerOptions consumerOptions) throws PGPException, IOException {
-            if (consumerOptions == null) {
-                throw new IllegalArgumentException("Consumer options cannot be null.");
-            }
-
-            return OpenPgpMessageInputStream.create(inputStream, consumerOptions);
-        }
-    }
-}
diff --git a/pgpainless-core/src/main/java/org/pgpainless/decryption_verification/DecryptionBuilderInterface.java b/pgpainless-core/src/main/java/org/pgpainless/decryption_verification/DecryptionBuilderInterface.java
deleted file mode 100644
index 07db42f0..00000000
--- a/pgpainless-core/src/main/java/org/pgpainless/decryption_verification/DecryptionBuilderInterface.java
+++ /dev/null
@@ -1,36 +0,0 @@
-// SPDX-FileCopyrightText: 2018 Paul Schaub <vanitasvitae@fsfe.org>
-//
-// SPDX-License-Identifier: Apache-2.0
-
-package org.pgpainless.decryption_verification;
-
-import java.io.IOException;
-import java.io.InputStream;
-import javax.annotation.Nonnull;
-
-import org.bouncycastle.openpgp.PGPException;
-
-public interface DecryptionBuilderInterface {
-
-    /**
-     * Create a {@link DecryptionStream} on an {@link InputStream} which contains the encrypted and/or signed data.
-     *
-     * @param inputStream encrypted and/or signed data.
-     * @return api handle
-     */
-    DecryptWith onInputStream(@Nonnull InputStream inputStream);
-
-    interface DecryptWith {
-
-        /**
-         * Add options for decryption / signature verification, such as keys, passphrases etc.
-         *
-         * @param consumerOptions consumer options
-         * @return decryption stream
-         * @throws PGPException in case of an OpenPGP related error
-         * @throws IOException in case of an IO error
-         */
-        DecryptionStream withOptions(ConsumerOptions consumerOptions) throws PGPException, IOException;
-
-    }
-}
diff --git a/pgpainless-core/src/main/kotlin/org/pgpainless/decryption_verification/DecryptionBuilder.kt b/pgpainless-core/src/main/kotlin/org/pgpainless/decryption_verification/DecryptionBuilder.kt
new file mode 100644
index 00000000..4934f5de
--- /dev/null
+++ b/pgpainless-core/src/main/kotlin/org/pgpainless/decryption_verification/DecryptionBuilder.kt
@@ -0,0 +1,26 @@
+// SPDX-FileCopyrightText: 2023 Paul Schaub <vanitasvitae@fsfe.org>
+//
+// SPDX-License-Identifier: Apache-2.0
+
+package org.pgpainless.decryption_verification
+
+import java.io.InputStream
+
+/**
+ * Builder class that takes an [InputStream] of ciphertext (or plaintext signed data)
+ * and combines it with a configured [ConsumerOptions] object to form a [DecryptionStream] which
+ * can be used to decrypt an OpenPGP message or verify signatures.
+ */
+class DecryptionBuilder: DecryptionBuilderInterface {
+
+    override fun onInputStream(inputStream: InputStream): DecryptionBuilderInterface.DecryptWith {
+        return DecryptWithImpl(inputStream)
+    }
+
+    class DecryptWithImpl(val inputStream: InputStream): DecryptionBuilderInterface.DecryptWith {
+
+        override fun withOptions(consumerOptions: ConsumerOptions): DecryptionStream {
+            return OpenPgpMessageInputStream.create(inputStream, consumerOptions)
+        }
+    }
+}
\ No newline at end of file
diff --git a/pgpainless-core/src/main/kotlin/org/pgpainless/decryption_verification/DecryptionBuilderInterface.kt b/pgpainless-core/src/main/kotlin/org/pgpainless/decryption_verification/DecryptionBuilderInterface.kt
new file mode 100644
index 00000000..c15f301e
--- /dev/null
+++ b/pgpainless-core/src/main/kotlin/org/pgpainless/decryption_verification/DecryptionBuilderInterface.kt
@@ -0,0 +1,34 @@
+// SPDX-FileCopyrightText: 2023 Paul Schaub <vanitasvitae@fsfe.org>
+//
+// SPDX-License-Identifier: Apache-2.0
+
+package org.pgpainless.decryption_verification
+
+import org.bouncycastle.openpgp.PGPException
+import java.io.IOException
+import java.io.InputStream
+
+interface DecryptionBuilderInterface {
+
+    /**
+     * Create a [DecryptionStream] on an [InputStream] which contains the encrypted and/or signed data.
+     *
+     * @param inputStream encrypted and/or signed data.
+     * @return api handle
+     */
+    fun onInputStream(inputStream: InputStream): DecryptWith
+
+    interface DecryptWith {
+
+        /**
+         * Add options for decryption / signature verification, such as keys, passphrases etc.
+         *
+         * @param consumerOptions consumer options
+         * @return decryption stream
+         * @throws PGPException in case of an OpenPGP related error
+         * @throws IOException in case of an IO error
+         */
+        @Throws(PGPException::class, IOException::class)
+        fun withOptions(consumerOptions: ConsumerOptions): DecryptionStream
+    }
+}
\ No newline at end of file