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 2f9162a9..6ee1ea4b 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
@@ -11,8 +11,10 @@ import org.bouncycastle.openpgp.PGPException;
 import org.bouncycastle.openpgp.PGPSecretKey;
 import org.bouncycastle.openpgp.PGPSignature;
 import org.pgpainless.algorithm.KeyFlag;
+import org.pgpainless.algorithm.SignatureType;
 import org.pgpainless.exception.WrongPassphraseException;
 import org.pgpainless.key.protection.SecretKeyRingProtector;
+import org.pgpainless.signature.subpackets.BaseSignatureSubpackets;
 import org.pgpainless.signature.subpackets.SelfSignatureSubpackets;
 
 public final class SignatureFactory {
@@ -109,6 +111,20 @@ public final class SignatureFactory {
         return certifier;
     }
 
+    public static UniversalSignatureBuilder universalSignature(
+            SignatureType signatureType,
+            PGPSecretKey signingKey,
+            SecretKeyRingProtector signingKeyProtector,
+            @Nullable BaseSignatureSubpackets.Callback callback)
+            throws WrongPassphraseException {
+        UniversalSignatureBuilder builder =
+                new UniversalSignatureBuilder(signatureType, signingKey, signingKeyProtector);
+
+        builder.applyCallback(callback);
+
+        return builder;
+    }
+
     private static boolean hasSignDataFlag(KeyFlag... flags) {
         if (flags == null) {
             return false;
@@ -120,4 +136,5 @@ public final class SignatureFactory {
         }
         return false;
     }
+
 }
diff --git a/pgpainless-core/src/main/java/org/pgpainless/signature/builder/UniversalSignatureBuilder.java b/pgpainless-core/src/main/java/org/pgpainless/signature/builder/UniversalSignatureBuilder.java
new file mode 100644
index 00000000..b674cba9
--- /dev/null
+++ b/pgpainless-core/src/main/java/org/pgpainless/signature/builder/UniversalSignatureBuilder.java
@@ -0,0 +1,57 @@
+// SPDX-FileCopyrightText: 2021 Paul Schaub <vanitasvitae@fsfe.org>
+//
+// SPDX-License-Identifier: Apache-2.0
+
+package org.pgpainless.signature.builder;
+
+import javax.annotation.Nullable;
+
+import org.bouncycastle.openpgp.PGPException;
+import org.bouncycastle.openpgp.PGPSecretKey;
+import org.bouncycastle.openpgp.PGPSignature;
+import org.bouncycastle.openpgp.PGPSignatureGenerator;
+import org.pgpainless.algorithm.SignatureType;
+import org.pgpainless.exception.WrongPassphraseException;
+import org.pgpainless.key.protection.SecretKeyRingProtector;
+import org.pgpainless.signature.subpackets.BaseSignatureSubpackets;
+import org.pgpainless.signature.subpackets.SignatureSubpacketGeneratorWrapper;
+
+/**
+ * Signature builder without restrictions on subpacket contents.
+ */
+public class UniversalSignatureBuilder extends AbstractSignatureBuilder<UniversalSignatureBuilder> {
+
+    public UniversalSignatureBuilder(SignatureType signatureType, PGPSecretKey signingKey, SecretKeyRingProtector protector)
+            throws WrongPassphraseException {
+        super(signatureType, signingKey, protector);
+    }
+
+    public UniversalSignatureBuilder(PGPSecretKey certificationKey, SecretKeyRingProtector protector, PGPSignature archetypeSignature)
+            throws WrongPassphraseException {
+        super(certificationKey, protector, archetypeSignature);
+    }
+
+    @Override
+    protected boolean isValidSignatureType(SignatureType type) {
+        return true;
+    }
+
+    public SignatureSubpacketGeneratorWrapper getHashedSubpackets() {
+        return hashedSubpackets;
+    }
+
+    public SignatureSubpacketGeneratorWrapper getUnhashedSubpackets() {
+        return unhashedSubpackets;
+    }
+
+    public void applyCallback(@Nullable BaseSignatureSubpackets.Callback callback) {
+        if (callback != null) {
+            callback.modifyHashedSubpackets(getHashedSubpackets());
+            callback.modifyUnhashedSubpackets(getUnhashedSubpackets());
+        }
+    }
+
+    public PGPSignatureGenerator getSignatureGenerator() throws PGPException {
+        return buildAndInitSignatureGenerator();
+    }
+}
diff --git a/pgpainless-core/src/main/java/org/pgpainless/signature/subpackets/BaseSignatureSubpackets.java b/pgpainless-core/src/main/java/org/pgpainless/signature/subpackets/BaseSignatureSubpackets.java
index 3b824f11..0f05b0d5 100644
--- a/pgpainless-core/src/main/java/org/pgpainless/signature/subpackets/BaseSignatureSubpackets.java
+++ b/pgpainless-core/src/main/java/org/pgpainless/signature/subpackets/BaseSignatureSubpackets.java
@@ -28,6 +28,16 @@ import org.pgpainless.algorithm.PublicKeyAlgorithm;
 
 public interface BaseSignatureSubpackets {
 
+    interface Callback {
+        default void modifyHashedSubpackets(SignatureSubpacketGeneratorWrapper subpackets) {
+
+        }
+
+        default void modifyUnhashedSubpackets(SignatureSubpacketGeneratorWrapper subpackets) {
+
+        }
+    }
+
     SignatureSubpacketGeneratorWrapper setIssuerFingerprintAndKeyId(PGPPublicKey key);
 
     SignatureSubpacketGeneratorWrapper setIssuerKeyId(long keyId);