diff --git a/pgpainless-core/src/main/java/org/pgpainless/key/gnu_dummy_s2k/GNUExtension.java b/pgpainless-core/src/main/java/org/pgpainless/key/gnu_dummy_s2k/GnuPGDummyExtension.java
similarity index 88%
rename from pgpainless-core/src/main/java/org/pgpainless/key/gnu_dummy_s2k/GNUExtension.java
rename to pgpainless-core/src/main/java/org/pgpainless/key/gnu_dummy_s2k/GnuPGDummyExtension.java
index e829bd7b..9f75bf7e 100644
--- a/pgpainless-core/src/main/java/org/pgpainless/key/gnu_dummy_s2k/GNUExtension.java
+++ b/pgpainless-core/src/main/java/org/pgpainless/key/gnu_dummy_s2k/GnuPGDummyExtension.java
@@ -6,7 +6,7 @@ package org.pgpainless.key.gnu_dummy_s2k;
 
 import org.bouncycastle.bcpg.S2K;
 
-public enum GNUExtension {
+public enum GnuPGDummyExtension {
 
     /**
      * Do not store the secret part at all.
@@ -21,7 +21,7 @@ public enum GNUExtension {
 
     private final int id;
 
-    GNUExtension(int id) {
+    GnuPGDummyExtension(int id) {
         this.id = id;
     }
 
diff --git a/pgpainless-core/src/main/java/org/pgpainless/key/gnu_dummy_s2k/GnuDummyKeyUtil.java b/pgpainless-core/src/main/java/org/pgpainless/key/gnu_dummy_s2k/GnuPGDummyKeyUtil.java
similarity index 81%
rename from pgpainless-core/src/main/java/org/pgpainless/key/gnu_dummy_s2k/GnuDummyKeyUtil.java
rename to pgpainless-core/src/main/java/org/pgpainless/key/gnu_dummy_s2k/GnuPGDummyKeyUtil.java
index 7817a676..3a913894 100644
--- a/pgpainless-core/src/main/java/org/pgpainless/key/gnu_dummy_s2k/GnuDummyKeyUtil.java
+++ b/pgpainless-core/src/main/java/org/pgpainless/key/gnu_dummy_s2k/GnuPGDummyKeyUtil.java
@@ -17,11 +17,15 @@ import java.util.Collection;
 import java.util.List;
 
 /**
- * This class can be used to remove private keys from secret keys.
+ * This class can be used to remove private keys from secret software-keys by replacing them with
+ * stub secret keys in the style of GnuPGs proprietary extensions.
+ *
+ * @see <a href="https://git.gnupg.org/cgi-bin/gitweb.cgi?p=gnupg.git;a=blob;f=doc/DETAILS;hb=HEAD#l1489">
+ *     GnuPGs doc/DETAILS - GNU extensions to the S2K algorithm</a>
  */
-public final class GnuDummyKeyUtil {
+public final class GnuPGDummyKeyUtil {
 
-    private GnuDummyKeyUtil() {
+    private GnuPGDummyKeyUtil() {
 
     }
 
@@ -45,18 +49,18 @@ public final class GnuDummyKeyUtil {
 
         /**
          * Remove all private keys that match the given {@link KeyFilter} from the key ring and replace them with
-         * GNU_DUMMY keys with S2K protection mode {@link GNUExtension#NO_PRIVATE_KEY}.
+         * GNU_DUMMY keys with S2K protection mode {@link GnuPGDummyExtension#NO_PRIVATE_KEY}.
          *
          * @param filter filter to select keys for removal
          * @return modified key ring
          */
         public PGPSecretKeyRing removePrivateKeys(KeyFilter filter) {
-            return replacePrivateKeys(GNUExtension.NO_PRIVATE_KEY, null, filter);
+            return replacePrivateKeys(GnuPGDummyExtension.NO_PRIVATE_KEY, null, filter);
         }
 
         /**
          * Remove all private keys that match the given {@link KeyFilter} from the key ring and replace them with
-         * GNU_DUMMY keys with S2K protection mode {@link GNUExtension#DIVERT_TO_CARD}.
+         * GNU_DUMMY keys with S2K protection mode {@link GnuPGDummyExtension#DIVERT_TO_CARD}.
          * This method will set the serial number of the card to 0x00000000000000000000000000000000.
          *
          * NOTE: This method does not actually move any keys to a card.
@@ -70,7 +74,7 @@ public final class GnuDummyKeyUtil {
 
         /**
          * Remove all private keys that match the given {@link KeyFilter} from the key ring and replace them with
-         * GNU_DUMMY keys with S2K protection mode {@link GNUExtension#DIVERT_TO_CARD}.
+         * GNU_DUMMY keys with S2K protection mode {@link GnuPGDummyExtension#DIVERT_TO_CARD}.
          * This method will include the card serial number into the encoded dummy key.
          *
          * NOTE: This method does not actually move any keys to a card.
@@ -83,10 +87,10 @@ public final class GnuDummyKeyUtil {
             if (cardSerialNumber != null && cardSerialNumber.length > 16) {
                 throw new IllegalArgumentException("Card serial number length cannot exceed 16 bytes.");
             }
-            return replacePrivateKeys(GNUExtension.DIVERT_TO_CARD, cardSerialNumber, filter);
+            return replacePrivateKeys(GnuPGDummyExtension.DIVERT_TO_CARD, cardSerialNumber, filter);
         }
 
-        private PGPSecretKeyRing replacePrivateKeys(GNUExtension extension, byte[] serial, KeyFilter filter) {
+        private PGPSecretKeyRing replacePrivateKeys(GnuPGDummyExtension extension, byte[] serial, KeyFilter filter) {
             byte[] encodedSerial = serial != null ? encodeSerial(serial) : null;
             S2K s2k = extensionToS2K(extension);
 
@@ -122,12 +126,16 @@ public final class GnuDummyKeyUtil {
             return encoded;
         }
 
-        private S2K extensionToS2K(@Nonnull GNUExtension extension) {
-            return S2K.gnuDummyS2K(extension == GNUExtension.DIVERT_TO_CARD ?
+        private S2K extensionToS2K(@Nonnull GnuPGDummyExtension extension) {
+            return S2K.gnuDummyS2K(extension == GnuPGDummyExtension.DIVERT_TO_CARD ?
                     S2K.GNUDummyParams.divertToCard() : S2K.GNUDummyParams.noPrivateKey());
         }
     }
 
+    /**
+     * Filter for selecting keys.
+     */
+    @FunctionalInterface
     public interface KeyFilter {
 
         /**
@@ -140,6 +148,7 @@ public final class GnuDummyKeyUtil {
 
         /**
          * Select any key.
+         *
          * @return filter
          */
         static KeyFilter any() {
diff --git a/pgpainless-core/src/test/java/org/pgpainless/decryption_verification/HardwareSecurityTest.java b/pgpainless-core/src/test/java/org/pgpainless/decryption_verification/HardwareSecurityTest.java
index f1606cec..a2160edf 100644
--- a/pgpainless-core/src/test/java/org/pgpainless/decryption_verification/HardwareSecurityTest.java
+++ b/pgpainless-core/src/test/java/org/pgpainless/decryption_verification/HardwareSecurityTest.java
@@ -17,7 +17,7 @@ import org.bouncycastle.openpgp.PGPSecretKeyRing;
 import org.junit.jupiter.api.Test;
 import org.pgpainless.PGPainless;
 import org.pgpainless.key.SubkeyIdentifier;
-import org.pgpainless.key.gnu_dummy_s2k.GnuDummyKeyUtil;
+import org.pgpainless.key.gnu_dummy_s2k.GnuPGDummyKeyUtil;
 import org.pgpainless.key.util.KeyIdUtil;
 
 public class HardwareSecurityTest {
@@ -53,8 +53,8 @@ public class HardwareSecurityTest {
         assertTrue(HardwareSecurity.getIdsOfHardwareBackedKeys(secretKeys).isEmpty());
         long encryptionKeyId = KeyIdUtil.fromLongKeyId("0AAD8F5891262F50");
 
-        PGPSecretKeyRing withHardwareBackedEncryptionKey = GnuDummyKeyUtil.modify(secretKeys)
-                .divertPrivateKeysToCard(GnuDummyKeyUtil.KeyFilter.only(encryptionKeyId));
+        PGPSecretKeyRing withHardwareBackedEncryptionKey = GnuPGDummyKeyUtil.modify(secretKeys)
+                .divertPrivateKeysToCard(GnuPGDummyKeyUtil.KeyFilter.only(encryptionKeyId));
 
         Set<SubkeyIdentifier> hardwareBackedKeys = HardwareSecurity
                 .getIdsOfHardwareBackedKeys(withHardwareBackedEncryptionKey);
@@ -67,8 +67,8 @@ public class HardwareSecurityTest {
         PGPSecretKeyRing secretKeys = PGPainless.readKeyRing().secretKeyRing(KEY);
         assertTrue(HardwareSecurity.getIdsOfHardwareBackedKeys(secretKeys).isEmpty());
 
-        PGPSecretKeyRing withHardwareBackedEncryptionKey = GnuDummyKeyUtil.modify(secretKeys)
-                .divertPrivateKeysToCard(GnuDummyKeyUtil.KeyFilter.any());
+        PGPSecretKeyRing withHardwareBackedEncryptionKey = GnuPGDummyKeyUtil.modify(secretKeys)
+                .divertPrivateKeysToCard(GnuPGDummyKeyUtil.KeyFilter.any());
         Set<SubkeyIdentifier> expected = new HashSet<>();
         for (PGPSecretKey key : secretKeys) {
             expected.add(new SubkeyIdentifier(secretKeys, key.getKeyID()));
diff --git a/pgpainless-core/src/test/java/org/pgpainless/key/gnu_dummy_s2k/GnuDummyKeyUtilTest.java b/pgpainless-core/src/test/java/org/pgpainless/key/gnu_dummy_s2k/GnuPGDummyKeyUtilTest.java
similarity index 93%
rename from pgpainless-core/src/test/java/org/pgpainless/key/gnu_dummy_s2k/GnuDummyKeyUtilTest.java
rename to pgpainless-core/src/test/java/org/pgpainless/key/gnu_dummy_s2k/GnuPGDummyKeyUtilTest.java
index 99966903..1fc3b892 100644
--- a/pgpainless-core/src/test/java/org/pgpainless/key/gnu_dummy_s2k/GnuDummyKeyUtilTest.java
+++ b/pgpainless-core/src/test/java/org/pgpainless/key/gnu_dummy_s2k/GnuPGDummyKeyUtilTest.java
@@ -17,7 +17,7 @@ import java.io.IOException;
 import static org.junit.jupiter.api.Assertions.assertArrayEquals;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 
-public class GnuDummyKeyUtilTest {
+public class GnuPGDummyKeyUtilTest {
     // normal, non-hw-backed key
     private static final String FULL_KEY = "-----BEGIN PGP PRIVATE KEY BLOCK-----\n" +
             "Version: PGPainless\n" +
@@ -153,8 +153,8 @@ public class GnuDummyKeyUtilTest {
         PGPSecretKeyRing secretKeys = PGPainless.readKeyRing().secretKeyRing(FULL_KEY);
         PGPSecretKeyRing expected = PGPainless.readKeyRing().secretKeyRing(ALL_KEYS_ON_CARD);
 
-        PGPSecretKeyRing onCard = GnuDummyKeyUtil.modify(secretKeys)
-                .divertPrivateKeysToCard(GnuDummyKeyUtil.KeyFilter.any(), cardSerial);
+        PGPSecretKeyRing onCard = GnuPGDummyKeyUtil.modify(secretKeys)
+                .divertPrivateKeysToCard(GnuPGDummyKeyUtil.KeyFilter.any(), cardSerial);
 
         for (PGPSecretKey key : onCard) {
             assertEquals(SecretKeyPacket.USAGE_SHA1, key.getS2KUsage());
@@ -170,8 +170,8 @@ public class GnuDummyKeyUtilTest {
         PGPSecretKeyRing secretKeys = PGPainless.readKeyRing().secretKeyRing(FULL_KEY);
         PGPSecretKeyRing expected = PGPainless.readKeyRing().secretKeyRing(PRIMARY_KEY_ON_CARD);
 
-        PGPSecretKeyRing onCard = GnuDummyKeyUtil.modify(secretKeys)
-                .divertPrivateKeysToCard(GnuDummyKeyUtil.KeyFilter.only(primaryKeyId), cardSerial);
+        PGPSecretKeyRing onCard = GnuPGDummyKeyUtil.modify(secretKeys)
+                .divertPrivateKeysToCard(GnuPGDummyKeyUtil.KeyFilter.only(primaryKeyId), cardSerial);
 
         assertArrayEquals(expected.getEncoded(), onCard.getEncoded());
     }
@@ -181,8 +181,8 @@ public class GnuDummyKeyUtilTest {
         PGPSecretKeyRing secretKeys = PGPainless.readKeyRing().secretKeyRing(FULL_KEY);
         PGPSecretKeyRing expected = PGPainless.readKeyRing().secretKeyRing(ENCRYPTION_KEY_ON_CARD);
 
-        PGPSecretKeyRing onCard = GnuDummyKeyUtil.modify(secretKeys)
-                .divertPrivateKeysToCard(GnuDummyKeyUtil.KeyFilter.only(encryptionKeyId), cardSerial);
+        PGPSecretKeyRing onCard = GnuPGDummyKeyUtil.modify(secretKeys)
+                .divertPrivateKeysToCard(GnuPGDummyKeyUtil.KeyFilter.only(encryptionKeyId), cardSerial);
 
         assertArrayEquals(expected.getEncoded(), onCard.getEncoded());
     }
@@ -192,8 +192,8 @@ public class GnuDummyKeyUtilTest {
         PGPSecretKeyRing secretKeys = PGPainless.readKeyRing().secretKeyRing(FULL_KEY);
         PGPSecretKeyRing expected = PGPainless.readKeyRing().secretKeyRing(SIGNATURE_KEY_ON_CARD);
 
-        PGPSecretKeyRing onCard = GnuDummyKeyUtil.modify(secretKeys)
-                .divertPrivateKeysToCard(GnuDummyKeyUtil.KeyFilter.only(signatureKeyId), cardSerial);
+        PGPSecretKeyRing onCard = GnuPGDummyKeyUtil.modify(secretKeys)
+                .divertPrivateKeysToCard(GnuPGDummyKeyUtil.KeyFilter.only(signatureKeyId), cardSerial);
 
         assertArrayEquals(expected.getEncoded(), onCard.getEncoded());
     }