diff --git a/pgpainless-core/src/main/java/org/pgpainless/signature/builder/CertificationSignatureBuilder.java b/pgpainless-core/src/main/java/org/pgpainless/signature/builder/CertificationSignatureBuilder.java
index f094c4fc..fd37d9d5 100644
--- a/pgpainless-core/src/main/java/org/pgpainless/signature/builder/CertificationSignatureBuilder.java
+++ b/pgpainless-core/src/main/java/org/pgpainless/signature/builder/CertificationSignatureBuilder.java
@@ -5,6 +5,7 @@
 package org.pgpainless.signature.builder;
 
 import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
 
 import org.bouncycastle.openpgp.PGPException;
 import org.bouncycastle.openpgp.PGPPublicKey;
@@ -34,6 +35,13 @@ public class CertificationSignatureBuilder extends AbstractSignatureBuilder<Cert
         return unhashedSubpackets;
     }
 
+    public void applyCallback(@Nullable SelfSignatureSubpackets.Callback callback) {
+        if (callback != null) {
+            callback.modifyHashedSubpackets(getHashedSubpackets());
+            callback.modifyUnhashedSubpackets(getUnhashedSubpackets());
+        }
+    }
+
     public PGPSignature build(PGPPublicKey certifiedKey, String userId) throws PGPException {
         return buildAndInitSignatureGenerator().generateCertification(userId, certifiedKey);
     }
diff --git a/pgpainless-core/src/main/java/org/pgpainless/signature/builder/DirectKeySignatureBuilder.java b/pgpainless-core/src/main/java/org/pgpainless/signature/builder/DirectKeySignatureBuilder.java
index cb5b8c32..f65c7bb8 100644
--- a/pgpainless-core/src/main/java/org/pgpainless/signature/builder/DirectKeySignatureBuilder.java
+++ b/pgpainless-core/src/main/java/org/pgpainless/signature/builder/DirectKeySignatureBuilder.java
@@ -4,6 +4,8 @@
 
 package org.pgpainless.signature.builder;
 
+import javax.annotation.Nullable;
+
 import org.bouncycastle.openpgp.PGPException;
 import org.bouncycastle.openpgp.PGPPublicKey;
 import org.bouncycastle.openpgp.PGPSecretKey;
@@ -31,6 +33,13 @@ public class DirectKeySignatureBuilder extends AbstractSignatureBuilder<DirectKe
         return unhashedSubpackets;
     }
 
+    public void applyCallback(@Nullable SelfSignatureSubpackets.Callback callback) {
+        if (callback != null) {
+            callback.modifyHashedSubpackets(getHashedSubpackets());
+            callback.modifyUnhashedSubpackets(getUnhashedSubpackets());
+        }
+    }
+
     public PGPSignature build(PGPPublicKey key) throws PGPException {
         return buildAndInitSignatureGenerator()
                 .generateCertification(key);
diff --git a/pgpainless-core/src/main/java/org/pgpainless/signature/builder/PrimaryKeyBindingSignatureBuilder.java b/pgpainless-core/src/main/java/org/pgpainless/signature/builder/PrimaryKeyBindingSignatureBuilder.java
index 8d8a6901..0f88dec4 100644
--- a/pgpainless-core/src/main/java/org/pgpainless/signature/builder/PrimaryKeyBindingSignatureBuilder.java
+++ b/pgpainless-core/src/main/java/org/pgpainless/signature/builder/PrimaryKeyBindingSignatureBuilder.java
@@ -4,6 +4,8 @@
 
 package org.pgpainless.signature.builder;
 
+import javax.annotation.Nullable;
+
 import org.bouncycastle.openpgp.PGPException;
 import org.bouncycastle.openpgp.PGPPublicKey;
 import org.bouncycastle.openpgp.PGPSecretKey;
@@ -28,6 +30,13 @@ public class PrimaryKeyBindingSignatureBuilder extends AbstractSignatureBuilder<
         return unhashedSubpackets;
     }
 
+    public void applyCallback(@Nullable SelfSignatureSubpackets.Callback callback) {
+        if (callback != null) {
+            callback.modifyHashedSubpackets(getHashedSubpackets());
+            callback.modifyUnhashedSubpackets(getUnhashedSubpackets());
+        }
+    }
+
     @Override
     protected boolean isValidSignatureType(SignatureType type) {
         return type == SignatureType.PRIMARYKEY_BINDING;
diff --git a/pgpainless-core/src/main/java/org/pgpainless/signature/builder/RevocationSignatureBuilder.java b/pgpainless-core/src/main/java/org/pgpainless/signature/builder/RevocationSignatureBuilder.java
index db263f07..51f62a1f 100644
--- a/pgpainless-core/src/main/java/org/pgpainless/signature/builder/RevocationSignatureBuilder.java
+++ b/pgpainless-core/src/main/java/org/pgpainless/signature/builder/RevocationSignatureBuilder.java
@@ -4,12 +4,15 @@
 
 package org.pgpainless.signature.builder;
 
+import javax.annotation.Nullable;
+
 import org.bouncycastle.openpgp.PGPSecretKey;
 import org.bouncycastle.openpgp.PGPSignature;
 import org.pgpainless.algorithm.SignatureType;
 import org.pgpainless.exception.WrongPassphraseException;
 import org.pgpainless.key.protection.SecretKeyRingProtector;
 import org.pgpainless.signature.subpackets.RevocationSignatureSubpackets;
+import org.pgpainless.signature.subpackets.SelfSignatureSubpackets;
 
 public class RevocationSignatureBuilder extends AbstractSignatureBuilder<RevocationSignatureBuilder> {
 
@@ -37,6 +40,13 @@ public class RevocationSignatureBuilder extends AbstractSignatureBuilder<Revocat
         return unhashedSubpackets;
     }
 
+    public void applyCallback(@Nullable RevocationSignatureSubpackets.Callback callback) {
+        if (callback != null) {
+            callback.modifyHashedSubpackets(getHashedSubpackets());
+            callback.modifyUnhashedSubpackets(getUnhashedSubpackets());
+        }
+    }
+
     public PGPSignature build() {
         return null;
     }
diff --git a/pgpainless-core/src/main/java/org/pgpainless/signature/builder/SignatureFactory.java b/pgpainless-core/src/main/java/org/pgpainless/signature/builder/SignatureFactory.java
index b113c161..2f9162a9 100644
--- a/pgpainless-core/src/main/java/org/pgpainless/signature/builder/SignatureFactory.java
+++ b/pgpainless-core/src/main/java/org/pgpainless/signature/builder/SignatureFactory.java
@@ -8,7 +8,6 @@ import java.io.IOException;
 import javax.annotation.Nullable;
 
 import org.bouncycastle.openpgp.PGPException;
-import org.bouncycastle.openpgp.PGPPublicKey;
 import org.bouncycastle.openpgp.PGPSecretKey;
 import org.bouncycastle.openpgp.PGPSignature;
 import org.pgpainless.algorithm.KeyFlag;
@@ -48,8 +47,9 @@ public final class SignatureFactory {
         SubkeyBindingSignatureBuilder subkeyBinder = bindSubkey(primaryKey, primaryKeyProtector, subkeyBindingSubpacketsCallback, flags);
 
         if (hasSignDataFlag(flags)) {
-            PGPSignature backsig = createPrimaryKeyBinding(
-                    subkey, subkeyProtector, primaryKeyBindingSubpacketsCallback, primaryKey.getPublicKey());
+            PGPSignature backsig = bindPrimaryKey(
+                    subkey, subkeyProtector, primaryKeyBindingSubpacketsCallback)
+                    .build(primaryKey.getPublicKey());
             subkeyBinder.getHashedSubpackets().addEmbeddedSignature(backsig);
         }
 
@@ -65,13 +65,9 @@ public final class SignatureFactory {
         }
         SubkeyBindingSignatureBuilder subkeyBinder = new SubkeyBindingSignatureBuilder(primaryKey, primaryKeyProtector);
         SelfSignatureSubpackets hashedSubpackets = subkeyBinder.getHashedSubpackets();
-        SelfSignatureSubpackets unhashedSubpackets = subkeyBinder.getUnhashedSubpackets();
         hashedSubpackets.setKeyFlags(flags);
 
-        if (subkeyBindingSubpacketsCallback != null) {
-            subkeyBindingSubpacketsCallback.modifyHashedSubpackets(hashedSubpackets);
-            subkeyBindingSubpacketsCallback.modifyUnhashedSubpackets(unhashedSubpackets);
-        }
+        subkeyBinder.applyCallback(subkeyBindingSubpacketsCallback);
 
         return subkeyBinder;
     }
@@ -82,24 +78,11 @@ public final class SignatureFactory {
             @Nullable SelfSignatureSubpackets.Callback primaryKeyBindingSubpacketsCallback) throws WrongPassphraseException {
         PrimaryKeyBindingSignatureBuilder primaryKeyBinder = new PrimaryKeyBindingSignatureBuilder(subkey, subkeyProtector);
 
-        if (primaryKeyBindingSubpacketsCallback != null) {
-            primaryKeyBindingSubpacketsCallback.modifyHashedSubpackets(primaryKeyBinder.getHashedSubpackets());
-            primaryKeyBindingSubpacketsCallback.modifyUnhashedSubpackets(primaryKeyBinder.getUnhashedSubpackets());
-        }
+        primaryKeyBinder.applyCallback(primaryKeyBindingSubpacketsCallback);
 
         return primaryKeyBinder;
     }
 
-    public static PGPSignature createPrimaryKeyBinding(
-            PGPSecretKey subkey,
-            SecretKeyRingProtector subkeyProtector,
-            @Nullable SelfSignatureSubpackets.Callback primaryKeyBindingSubpacketsCallback,
-            PGPPublicKey primaryKey)
-            throws PGPException {
-        return bindPrimaryKey(subkey, subkeyProtector, primaryKeyBindingSubpacketsCallback)
-                .build(primaryKey);
-    }
-
     public static CertificationSignatureBuilder selfCertifyUserId(
             PGPSecretKey primaryKey,
             SecretKeyRingProtector primaryKeyProtector,
@@ -108,10 +91,8 @@ public final class SignatureFactory {
 
         CertificationSignatureBuilder certifier = new CertificationSignatureBuilder(primaryKey, primaryKeyProtector);
         certifier.getHashedSubpackets().setKeyFlags(flags);
-        if (selfSignatureCallback != null) {
-            selfSignatureCallback.modifyHashedSubpackets(certifier.getHashedSubpackets());
-            selfSignatureCallback.modifyUnhashedSubpackets(certifier.getUnhashedSubpackets());
-        }
+        certifier.applyCallback(selfSignatureCallback);
+
         return certifier;
     }
 
@@ -120,22 +101,12 @@ public final class SignatureFactory {
             SecretKeyRingProtector primaryKeyProtector,
             @Nullable SelfSignatureSubpackets.Callback selfSignatureCallback,
             PGPSignature oldCertification) throws WrongPassphraseException {
-        CertificationSignatureBuilder certifier =
-                new CertificationSignatureBuilder(primaryKey, primaryKeyProtector, oldCertification);
+        CertificationSignatureBuilder certifier = new CertificationSignatureBuilder(
+                primaryKey, primaryKeyProtector, oldCertification);
 
-        // TODO
-        return null;
-    }
+        certifier.applyCallback(selfSignatureCallback);
 
-    public static PGPSignature createUserIdSelfCertification(
-            String userId,
-            PGPSecretKey primaryKey,
-            SecretKeyRingProtector primaryKeyProtector,
-            @Nullable SelfSignatureSubpackets.Callback selfSignatureCallback,
-            KeyFlag... flags)
-            throws PGPException {
-        return selfCertifyUserId(primaryKey, primaryKeyProtector, selfSignatureCallback, flags)
-                .build(primaryKey.getPublicKey(), userId);
+        return certifier;
     }
 
     private static boolean hasSignDataFlag(KeyFlag... flags) {
diff --git a/pgpainless-core/src/main/java/org/pgpainless/signature/builder/SubkeyBindingSignatureBuilder.java b/pgpainless-core/src/main/java/org/pgpainless/signature/builder/SubkeyBindingSignatureBuilder.java
index fad7e31b..be73d6f1 100644
--- a/pgpainless-core/src/main/java/org/pgpainless/signature/builder/SubkeyBindingSignatureBuilder.java
+++ b/pgpainless-core/src/main/java/org/pgpainless/signature/builder/SubkeyBindingSignatureBuilder.java
@@ -4,6 +4,8 @@
 
 package org.pgpainless.signature.builder;
 
+import javax.annotation.Nullable;
+
 import org.bouncycastle.openpgp.PGPException;
 import org.bouncycastle.openpgp.PGPPublicKey;
 import org.bouncycastle.openpgp.PGPSecretKey;
@@ -33,6 +35,13 @@ public class SubkeyBindingSignatureBuilder extends AbstractSignatureBuilder<Subk
         return unhashedSubpackets;
     }
 
+    public void applyCallback(@Nullable SelfSignatureSubpackets.Callback callback) {
+        if (callback != null) {
+            callback.modifyHashedSubpackets(getHashedSubpackets());
+            callback.modifyUnhashedSubpackets(getUnhashedSubpackets());
+        }
+    }
+
     public PGPSignature build(PGPPublicKey subkey) throws PGPException {
         return buildAndInitSignatureGenerator()
                 .generateCertification(publicSigningKey, subkey);
diff --git a/pgpainless-core/src/main/java/org/pgpainless/signature/consumer/package-info.java b/pgpainless-core/src/main/java/org/pgpainless/signature/consumer/package-info.java
new file mode 100644
index 00000000..e8e53285
--- /dev/null
+++ b/pgpainless-core/src/main/java/org/pgpainless/signature/consumer/package-info.java
@@ -0,0 +1,8 @@
+// SPDX-FileCopyrightText: 2021 Paul Schaub <vanitasvitae@fsfe.org>
+//
+// SPDX-License-Identifier: Apache-2.0
+
+/**
+ * Classes related to OpenPGP signature verification.
+ */
+package org.pgpainless.signature.consumer;