diff --git a/sop-java/src/main/java/sop/enums/InlineSignAs.java b/sop-java/src/main/java/sop/enums/InlineSignAs.java
new file mode 100644
index 0000000..b0b55dc
--- /dev/null
+++ b/sop-java/src/main/java/sop/enums/InlineSignAs.java
@@ -0,0 +1,24 @@
+// SPDX-FileCopyrightText: 2022 Paul Schaub <vanitasvitae@fsfe.org>
+//
+// SPDX-License-Identifier: Apache-2.0
+
+package sop.enums;
+
+public enum InlineSignAs {
+
+    /**
+     * Signature is made over the binary message.
+     */
+    Binary,
+
+    /**
+     * Signature is made over the message in text mode.
+     */
+    Text,
+
+    /**
+     * Signature is made using the Cleartext Signature Framework.
+     */
+    CleartextSigned,
+}
+
diff --git a/sop-java/src/main/java/sop/operation/AbstractSign.java b/sop-java/src/main/java/sop/operation/AbstractSign.java
new file mode 100644
index 0000000..4fd0b8a
--- /dev/null
+++ b/sop-java/src/main/java/sop/operation/AbstractSign.java
@@ -0,0 +1,92 @@
+// SPDX-FileCopyrightText: 2022 Paul Schaub <vanitasvitae@fsfe.org>
+//
+// SPDX-License-Identifier: Apache-2.0
+
+package sop.operation;
+
+import sop.ReadyWithResult;
+import sop.SigningResult;
+import sop.exception.SOPGPException;
+
+import java.io.ByteArrayInputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.nio.charset.Charset;
+
+public interface AbstractSign<T> {
+
+    /**
+     * Disable ASCII armor encoding.
+     *
+     * @return builder instance
+     */
+    Sign noArmor();
+
+    /**
+     * Add one or more signing keys.
+     *
+     * @param key input stream containing encoded keys
+     * @return builder instance
+     *
+     * @throws sop.exception.SOPGPException.KeyIsProtected if the key is password protected
+     * @throws sop.exception.SOPGPException.BadData if the {@link InputStream} does not contain an OpenPGP key
+     * @throws IOException in case of an IO error
+     */
+    T key(InputStream key) throws SOPGPException.KeyIsProtected, SOPGPException.BadData, IOException;
+
+    /**
+     * Add one or more signing keys.
+     *
+     * @param key byte array containing encoded keys
+     * @return builder instance
+     *
+     * @throws sop.exception.SOPGPException.KeyIsProtected if the key is password protected
+     * @throws sop.exception.SOPGPException.BadData if the byte array does not contain an OpenPGP key
+     * @throws IOException in case of an IO error
+     */
+    default T key(byte[] key) throws SOPGPException.KeyIsProtected, SOPGPException.BadData, IOException {
+        return key(new ByteArrayInputStream(key));
+    }
+
+    /**
+     * Provide the decryption password for the secret key.
+     *
+     * @param password password
+     * @return builder instance
+     */
+    default T withKeyPassword(String password) {
+        return withKeyPassword(password.getBytes(Charset.forName("UTF8")));
+    }
+
+    /**
+     * Provide the decryption password for the secret key.
+     *
+     * @param password password
+     * @return builder instance
+     */
+    T withKeyPassword(byte[] password);
+
+    /**
+     * Signs data.
+     *
+     * @param data input stream containing data
+     * @return ready
+     *
+     * @throws IOException in case of an IO error
+     * @throws sop.exception.SOPGPException.ExpectedText if text data was expected, but binary data was encountered
+     */
+    ReadyWithResult<SigningResult> data(InputStream data) throws IOException, SOPGPException.ExpectedText;
+
+    /**
+     * Signs data.
+     *
+     * @param data byte array containing data
+     * @return ready
+     *
+     * @throws IOException in case of an IO error
+     * @throws sop.exception.SOPGPException.ExpectedText if text data was expected, but binary data was encountered
+     */
+    default ReadyWithResult<SigningResult> data(byte[] data) throws IOException, SOPGPException.ExpectedText {
+        return data(new ByteArrayInputStream(data));
+    }
+}
diff --git a/sop-java/src/main/java/sop/operation/InlineSign.java b/sop-java/src/main/java/sop/operation/InlineSign.java
index ed1f90b..17bf80f 100644
--- a/sop-java/src/main/java/sop/operation/InlineSign.java
+++ b/sop-java/src/main/java/sop/operation/InlineSign.java
@@ -4,6 +4,22 @@
 
 package sop.operation;
 
-public interface InlineSign {
+import sop.enums.InlineSignAs;
+import sop.exception.SOPGPException;
+
+import java.io.InputStream;
+
+public interface InlineSign extends AbstractSign<InlineSign> {
+
+    /**
+     * Sets the signature mode.
+     * Note: This method has to be called before {@link #key(InputStream)} is called.
+     *
+     * @param mode signature mode
+     * @return builder instance
+     *
+     * @throws sop.exception.SOPGPException.UnsupportedOption if this option is not supported
+     */
+    Sign mode(InlineSignAs mode) throws SOPGPException.UnsupportedOption;
 
 }
diff --git a/sop-java/src/main/java/sop/operation/Sign.java b/sop-java/src/main/java/sop/operation/Sign.java
index f02e709..28a8f72 100644
--- a/sop-java/src/main/java/sop/operation/Sign.java
+++ b/sop-java/src/main/java/sop/operation/Sign.java
@@ -4,24 +4,12 @@
 
 package sop.operation;
 
-import java.io.ByteArrayInputStream;
-import java.io.IOException;
-import java.io.InputStream;
-import java.nio.charset.Charset;
-
-import sop.ReadyWithResult;
-import sop.SigningResult;
 import sop.enums.SignAs;
 import sop.exception.SOPGPException;
 
-public interface Sign {
+import java.io.InputStream;
 
-    /**
-     * Disable ASCII armor encoding.
-     *
-     * @return builder instance
-     */
-    Sign noArmor();
+public interface Sign extends AbstractSign<Sign> {
 
     /**
      * Sets the signature mode.
@@ -34,71 +22,4 @@ public interface Sign {
      */
     Sign mode(SignAs mode) throws SOPGPException.UnsupportedOption;
 
-    /**
-     * Add one or more signing keys.
-     *
-     * @param key input stream containing encoded keys
-     * @return builder instance
-     *
-     * @throws sop.exception.SOPGPException.KeyIsProtected if the key is password protected
-     * @throws sop.exception.SOPGPException.BadData if the {@link InputStream} does not contain an OpenPGP key
-     * @throws IOException in case of an IO error
-     */
-    Sign key(InputStream key) throws SOPGPException.KeyIsProtected, SOPGPException.BadData, IOException;
-
-    /**
-     * Add one or more signing keys.
-     *
-     * @param key byte array containing encoded keys
-     * @return builder instance
-     *
-     * @throws sop.exception.SOPGPException.KeyIsProtected if the key is password protected
-     * @throws sop.exception.SOPGPException.BadData if the byte array does not contain an OpenPGP key
-     * @throws IOException in case of an IO error
-     */
-    default Sign key(byte[] key) throws SOPGPException.KeyIsProtected, SOPGPException.BadData, IOException {
-        return key(new ByteArrayInputStream(key));
-    }
-
-    /**
-     * Provide the decryption password for the secret key.
-     *
-     * @param password password
-     * @return builder instance
-     */
-    default Sign withKeyPassword(String password) {
-        return withKeyPassword(password.getBytes(Charset.forName("UTF8")));
-    }
-
-    /**
-     * Provide the decryption password for the secret key.
-     *
-     * @param password password
-     * @return builder instance
-     */
-    Sign withKeyPassword(byte[] password);
-
-    /**
-     * Signs data.
-     *
-     * @param data input stream containing data
-     * @return ready
-     *
-     * @throws IOException in case of an IO error
-     * @throws sop.exception.SOPGPException.ExpectedText if text data was expected, but binary data was encountered
-     */
-    ReadyWithResult<SigningResult> data(InputStream data) throws IOException, SOPGPException.ExpectedText;
-
-    /**
-     * Signs data.
-     *
-     * @param data byte array containing data
-     * @return ready
-     *
-     * @throws IOException in case of an IO error
-     * @throws sop.exception.SOPGPException.ExpectedText if text data was expected, but binary data was encountered
-     */
-    default ReadyWithResult<SigningResult> data(byte[] data) throws IOException, SOPGPException.ExpectedText {
-        return data(new ByteArrayInputStream(data));
-    }
 }