diff --git a/pgpainless-core/src/main/java/org/pgpainless/PGPainless.java b/pgpainless-core/src/main/java/org/pgpainless/PGPainless.java
index 5c841c7b..ace68e81 100644
--- a/pgpainless-core/src/main/java/org/pgpainless/PGPainless.java
+++ b/pgpainless-core/src/main/java/org/pgpainless/PGPainless.java
@@ -17,7 +17,6 @@ package org.pgpainless;
 
 import java.io.IOException;
 import java.util.Date;
-
 import javax.annotation.Nonnull;
 
 import org.bouncycastle.openpgp.PGPKeyRing;
@@ -38,7 +37,11 @@ import org.pgpainless.signature.cleartext_signatures.VerifyCleartextSignatures;
 import org.pgpainless.signature.cleartext_signatures.VerifyCleartextSignaturesImpl;
 import org.pgpainless.util.ArmorUtils;
 
-public class PGPainless {
+public final class PGPainless {
+
+    private PGPainless() {
+
+    }
 
     /**
      * Generate a new OpenPGP key ring.
diff --git a/pgpainless-core/src/main/java/org/pgpainless/key/KeyRingValidator.java b/pgpainless-core/src/main/java/org/pgpainless/key/KeyRingValidator.java
index fa0984f6..cc5d0997 100644
--- a/pgpainless-core/src/main/java/org/pgpainless/key/KeyRingValidator.java
+++ b/pgpainless-core/src/main/java/org/pgpainless/key/KeyRingValidator.java
@@ -36,7 +36,11 @@ import org.pgpainless.signature.SignatureCreationDateComparator;
 import org.pgpainless.signature.SignatureValidator;
 import org.pgpainless.util.CollectionUtils;
 
-public class KeyRingValidator {
+public final class KeyRingValidator {
+
+    private KeyRingValidator() {
+
+    }
 
     private static final Logger LOGGER = Logger.getLogger(KeyRingValidator.class.getName());
 
diff --git a/pgpainless-core/src/main/java/org/pgpainless/key/protection/UnlockSecretKey.java b/pgpainless-core/src/main/java/org/pgpainless/key/protection/UnlockSecretKey.java
index 421183de..8e45b0c8 100644
--- a/pgpainless-core/src/main/java/org/pgpainless/key/protection/UnlockSecretKey.java
+++ b/pgpainless-core/src/main/java/org/pgpainless/key/protection/UnlockSecretKey.java
@@ -23,7 +23,11 @@ import org.pgpainless.exception.WrongPassphraseException;
 import org.pgpainless.key.info.KeyInfo;
 import org.pgpainless.util.Passphrase;
 
-public class UnlockSecretKey {
+public final class UnlockSecretKey {
+
+    private UnlockSecretKey() {
+
+    }
 
     public static PGPPrivateKey unlockSecretKey(PGPSecretKey secretKey, SecretKeyRingProtector protector)
             throws WrongPassphraseException {
diff --git a/pgpainless-core/src/main/java/org/pgpainless/key/util/KeyIdUtil.java b/pgpainless-core/src/main/java/org/pgpainless/key/util/KeyIdUtil.java
index 650bf7b0..40decde7 100644
--- a/pgpainless-core/src/main/java/org/pgpainless/key/util/KeyIdUtil.java
+++ b/pgpainless-core/src/main/java/org/pgpainless/key/util/KeyIdUtil.java
@@ -18,7 +18,11 @@ package org.pgpainless.key.util;
 import java.math.BigInteger;
 import java.util.regex.Pattern;
 
-public class KeyIdUtil {
+public final class KeyIdUtil {
+
+    private KeyIdUtil() {
+
+    }
 
     private static final Pattern LONG_KEY_ID = Pattern.compile("^[0-9A-Fa-f]{16}$");
 
diff --git a/pgpainless-core/src/main/java/org/pgpainless/key/util/KeyRingUtils.java b/pgpainless-core/src/main/java/org/pgpainless/key/util/KeyRingUtils.java
index c7872589..db3e4898 100644
--- a/pgpainless-core/src/main/java/org/pgpainless/key/util/KeyRingUtils.java
+++ b/pgpainless-core/src/main/java/org/pgpainless/key/util/KeyRingUtils.java
@@ -35,7 +35,11 @@ import org.bouncycastle.openpgp.PGPSecretKeyRingCollection;
 import org.pgpainless.key.protection.SecretKeyRingProtector;
 import org.pgpainless.key.protection.UnlockSecretKey;
 
-public class KeyRingUtils {
+public final class KeyRingUtils {
+
+    private KeyRingUtils() {
+
+    }
 
     /**
      * Return the primary {@link PGPSecretKey} from the provided {@link PGPSecretKeyRing}.
diff --git a/pgpainless-core/src/main/java/org/pgpainless/key/util/OpenPgpKeyAttributeUtil.java b/pgpainless-core/src/main/java/org/pgpainless/key/util/OpenPgpKeyAttributeUtil.java
index 573c163d..0cd4fb21 100644
--- a/pgpainless-core/src/main/java/org/pgpainless/key/util/OpenPgpKeyAttributeUtil.java
+++ b/pgpainless-core/src/main/java/org/pgpainless/key/util/OpenPgpKeyAttributeUtil.java
@@ -26,7 +26,11 @@ import org.bouncycastle.openpgp.PGPSignature;
 import org.pgpainless.algorithm.HashAlgorithm;
 import org.pgpainless.algorithm.SignatureType;
 
-public class OpenPgpKeyAttributeUtil {
+public final class OpenPgpKeyAttributeUtil {
+
+    private OpenPgpKeyAttributeUtil() {
+
+    }
 
     public static List<HashAlgorithm> getPreferredHashAlgorithms(PGPPublicKey publicKey) {
         List<HashAlgorithm> hashAlgorithms = new ArrayList<>();
diff --git a/pgpainless-core/src/main/java/org/pgpainless/signature/SignatureChainValidator.java b/pgpainless-core/src/main/java/org/pgpainless/signature/SignatureChainValidator.java
index e6a3a060..927726ce 100644
--- a/pgpainless-core/src/main/java/org/pgpainless/signature/SignatureChainValidator.java
+++ b/pgpainless-core/src/main/java/org/pgpainless/signature/SignatureChainValidator.java
@@ -42,7 +42,11 @@ import org.pgpainless.signature.subpackets.SignatureSubpacketsUtil;
  * Its responsibilities are checking if a signing key was eligible to create a certain signature
  * and if the signature is valid at the time of validation.
  */
-public class SignatureChainValidator {
+public final class SignatureChainValidator {
+
+    private SignatureChainValidator() {
+
+    }
 
     private static final Logger LOGGER = Logger.getLogger(SignatureChainValidator.class.getName());
 
diff --git a/pgpainless-core/src/main/java/org/pgpainless/signature/SignaturePicker.java b/pgpainless-core/src/main/java/org/pgpainless/signature/SignaturePicker.java
index dc9b99af..6f73d9b0 100644
--- a/pgpainless-core/src/main/java/org/pgpainless/signature/SignaturePicker.java
+++ b/pgpainless-core/src/main/java/org/pgpainless/signature/SignaturePicker.java
@@ -41,7 +41,11 @@ import org.pgpainless.util.CollectionUtils;
  *    [User Attribute [Signature ...] ...]
  *    [[Subkey [Binding-Signature-Revocation] Primary-Key-Binding-Signature] ...]
  */
-public class SignaturePicker {
+public final class SignaturePicker {
+
+    private SignaturePicker() {
+
+    }
 
     /**
      * Pick the, at validation date most recent valid key revocation signature.
diff --git a/pgpainless-core/src/main/java/org/pgpainless/signature/SignatureUtils.java b/pgpainless-core/src/main/java/org/pgpainless/signature/SignatureUtils.java
index f3337af3..6ac18175 100644
--- a/pgpainless-core/src/main/java/org/pgpainless/signature/SignatureUtils.java
+++ b/pgpainless-core/src/main/java/org/pgpainless/signature/SignatureUtils.java
@@ -52,7 +52,11 @@ import org.pgpainless.util.ArmorUtils;
 /**
  * Utility methods related to signatures.
  */
-public class SignatureUtils {
+public final class SignatureUtils {
+
+    private SignatureUtils() {
+
+    }
 
     /**
      * Return a signature generator for the provided signing key.
diff --git a/pgpainless-core/src/main/java/org/pgpainless/signature/subpackets/SignatureSubpacketGeneratorUtil.java b/pgpainless-core/src/main/java/org/pgpainless/signature/subpackets/SignatureSubpacketGeneratorUtil.java
index a2a07ffe..66aa4b50 100644
--- a/pgpainless-core/src/main/java/org/pgpainless/signature/subpackets/SignatureSubpacketGeneratorUtil.java
+++ b/pgpainless-core/src/main/java/org/pgpainless/signature/subpackets/SignatureSubpacketGeneratorUtil.java
@@ -29,7 +29,11 @@ import org.pgpainless.algorithm.KeyFlag;
 /**
  * Utility class that helps dealing with BCs SignatureSubpacketGenerator class.
  */
-public class SignatureSubpacketGeneratorUtil {
+public final class SignatureSubpacketGeneratorUtil {
+
+    private SignatureSubpacketGeneratorUtil() {
+
+    }
 
     /**
      * Return a list of {@link SignatureSubpacket SignatureSubpackets} from the subpacket generator, which correspond
diff --git a/pgpainless-core/src/main/java/org/pgpainless/signature/subpackets/SignatureSubpacketsUtil.java b/pgpainless-core/src/main/java/org/pgpainless/signature/subpackets/SignatureSubpacketsUtil.java
index 846635fd..1fb68f20 100644
--- a/pgpainless-core/src/main/java/org/pgpainless/signature/subpackets/SignatureSubpacketsUtil.java
+++ b/pgpainless-core/src/main/java/org/pgpainless/signature/subpackets/SignatureSubpacketsUtil.java
@@ -62,7 +62,11 @@ import org.pgpainless.signature.SignatureUtils;
  * Since rfc4880 is not always clear about where a signature subpacket can be located (hashed/unhashed area),
  * this class makes some educated guesses as to where the subpacket may be found when necessary.
  */
-public class SignatureSubpacketsUtil {
+public final class SignatureSubpacketsUtil {
+
+    private SignatureSubpacketsUtil() {
+
+    }
 
     /**
      * Return the issuer-fingerprint subpacket of the signature.
diff --git a/pgpainless-core/src/main/java/org/pgpainless/util/ArmorUtils.java b/pgpainless-core/src/main/java/org/pgpainless/util/ArmorUtils.java
index 3f9aa703..18b33574 100644
--- a/pgpainless-core/src/main/java/org/pgpainless/util/ArmorUtils.java
+++ b/pgpainless-core/src/main/java/org/pgpainless/util/ArmorUtils.java
@@ -39,7 +39,7 @@ import org.bouncycastle.util.io.Streams;
 import org.pgpainless.algorithm.HashAlgorithm;
 import org.pgpainless.key.OpenPgpV4Fingerprint;
 
-public class ArmorUtils {
+public final class ArmorUtils {
 
     // MessageIDs are 32 printable characters
     private static final Pattern PATTERN_MESSAGE_ID = Pattern.compile("^\\S{32}$");
@@ -50,6 +50,10 @@ public class ArmorUtils {
     public static final String HEADER_HASH = "Hash";
     public static final String HEADER_CHARSET = "Charset";
 
+    private ArmorUtils() {
+
+    }
+
     public static String toAsciiArmoredString(PGPSecretKeyRing secretKeys) throws IOException {
         MultiMap<String, String> header = keyToHeader(secretKeys);
         return toAsciiArmoredString(secretKeys.getEncoded(), header);
diff --git a/pgpainless-core/src/main/java/org/pgpainless/util/ArmoredInputStreamFactory.java b/pgpainless-core/src/main/java/org/pgpainless/util/ArmoredInputStreamFactory.java
index 6228a885..7ab5f867 100644
--- a/pgpainless-core/src/main/java/org/pgpainless/util/ArmoredInputStreamFactory.java
+++ b/pgpainless-core/src/main/java/org/pgpainless/util/ArmoredInputStreamFactory.java
@@ -20,7 +20,11 @@ import java.io.InputStream;
 
 import org.bouncycastle.bcpg.ArmoredInputStream;
 
-public class ArmoredInputStreamFactory {
+public final class ArmoredInputStreamFactory {
+
+    private ArmoredInputStreamFactory() {
+
+    }
 
     public static ArmoredInputStream get(InputStream inputStream) throws IOException {
         if (inputStream instanceof CRCingArmoredInputStreamWrapper) {
diff --git a/pgpainless-core/src/main/java/org/pgpainless/util/ArmoredOutputStreamFactory.java b/pgpainless-core/src/main/java/org/pgpainless/util/ArmoredOutputStreamFactory.java
index 22e68431..1c54306c 100644
--- a/pgpainless-core/src/main/java/org/pgpainless/util/ArmoredOutputStreamFactory.java
+++ b/pgpainless-core/src/main/java/org/pgpainless/util/ArmoredOutputStreamFactory.java
@@ -23,12 +23,16 @@ import org.bouncycastle.bcpg.ArmoredOutputStream;
  * Factory to create configured {@link ArmoredOutputStream ArmoredOutputStreams}.
  * The configuration entails setting custom version and comment headers.
  */
-public class ArmoredOutputStreamFactory {
+public final class ArmoredOutputStreamFactory {
 
     public static final String PGPAINLESS = "PGPainless";
     private static String VERSION = PGPAINLESS;
     public static String[] COMMENT = new String[0];
 
+    private ArmoredOutputStreamFactory() {
+
+    }
+
     /**
      * Wrap an {@link OutputStream} inside a preconfigured {@link ArmoredOutputStream}.
      *
diff --git a/pgpainless-core/src/main/java/org/pgpainless/util/BCUtil.java b/pgpainless-core/src/main/java/org/pgpainless/util/BCUtil.java
index b43236ff..8800b755 100644
--- a/pgpainless-core/src/main/java/org/pgpainless/util/BCUtil.java
+++ b/pgpainless-core/src/main/java/org/pgpainless/util/BCUtil.java
@@ -19,7 +19,11 @@ import org.bouncycastle.asn1.ASN1ObjectIdentifier;
 import org.bouncycastle.bcpg.ECPublicBCPGKey;
 import org.bouncycastle.openpgp.PGPPublicKey;
 
-public class BCUtil {
+public final class BCUtil {
+
+    private BCUtil() {
+
+    }
 
     /**
      * Utility method to get the bit strength of OpenPGP keys.
diff --git a/pgpainless-core/src/main/java/org/pgpainless/util/CollectionUtils.java b/pgpainless-core/src/main/java/org/pgpainless/util/CollectionUtils.java
index bf687229..6ad81991 100644
--- a/pgpainless-core/src/main/java/org/pgpainless/util/CollectionUtils.java
+++ b/pgpainless-core/src/main/java/org/pgpainless/util/CollectionUtils.java
@@ -19,7 +19,11 @@ import java.util.ArrayList;
 import java.util.Iterator;
 import java.util.List;
 
-public class CollectionUtils {
+public final class CollectionUtils {
+
+    private CollectionUtils() {
+
+    }
 
     public static <I> List<I> iteratorToList(Iterator<I> iterator) {
         List<I> items = new ArrayList<>();
diff --git a/pgpainless-core/src/main/java/org/pgpainless/util/DateUtil.java b/pgpainless-core/src/main/java/org/pgpainless/util/DateUtil.java
index 1b04f476..cfc6cc3a 100644
--- a/pgpainless-core/src/main/java/org/pgpainless/util/DateUtil.java
+++ b/pgpainless-core/src/main/java/org/pgpainless/util/DateUtil.java
@@ -20,8 +20,11 @@ import java.text.SimpleDateFormat;
 import java.util.Date;
 import java.util.TimeZone;
 
-public class DateUtil {
+public final class DateUtil {
 
+    private DateUtil() {
+
+    }
     public static SimpleDateFormat UTC_PARSER = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss z");
     static {
         UTC_PARSER.setTimeZone(TimeZone.getTimeZone("UTC"));
diff --git a/pgpainless-core/src/main/java/org/pgpainless/util/selection/keyring/impl/ExactUserId.java b/pgpainless-core/src/main/java/org/pgpainless/util/selection/keyring/impl/ExactUserId.java
index 4501328d..4edc7cb5 100644
--- a/pgpainless-core/src/main/java/org/pgpainless/util/selection/keyring/impl/ExactUserId.java
+++ b/pgpainless-core/src/main/java/org/pgpainless/util/selection/keyring/impl/ExactUserId.java
@@ -22,7 +22,11 @@ import org.bouncycastle.openpgp.PGPSecretKeyRing;
 import org.pgpainless.util.selection.keyring.PublicKeyRingSelectionStrategy;
 import org.pgpainless.util.selection.keyring.SecretKeyRingSelectionStrategy;
 
-public class ExactUserId {
+public final class ExactUserId {
+
+    private ExactUserId() {
+
+    }
 
     public static class PubRingSelectionStrategy extends PublicKeyRingSelectionStrategy<String> {
 
diff --git a/pgpainless-core/src/main/java/org/pgpainless/util/selection/keyring/impl/Whitelist.java b/pgpainless-core/src/main/java/org/pgpainless/util/selection/keyring/impl/Whitelist.java
index 1663706a..2d8a6ed9 100644
--- a/pgpainless-core/src/main/java/org/pgpainless/util/selection/keyring/impl/Whitelist.java
+++ b/pgpainless-core/src/main/java/org/pgpainless/util/selection/keyring/impl/Whitelist.java
@@ -24,7 +24,11 @@ import org.pgpainless.util.selection.keyring.PublicKeyRingSelectionStrategy;
 import org.pgpainless.util.selection.keyring.SecretKeyRingSelectionStrategy;
 import org.pgpainless.util.MultiMap;
 
-public class Whitelist {
+public final class Whitelist {
+
+    private Whitelist() {
+
+    }
 
     public static class PubRingSelectionStrategy<O> extends PublicKeyRingSelectionStrategy<O> {
 
diff --git a/pgpainless-core/src/main/java/org/pgpainless/util/selection/keyring/impl/Wildcard.java b/pgpainless-core/src/main/java/org/pgpainless/util/selection/keyring/impl/Wildcard.java
index 7337639c..23562afe 100644
--- a/pgpainless-core/src/main/java/org/pgpainless/util/selection/keyring/impl/Wildcard.java
+++ b/pgpainless-core/src/main/java/org/pgpainless/util/selection/keyring/impl/Wildcard.java
@@ -20,7 +20,11 @@ import org.bouncycastle.openpgp.PGPSecretKeyRing;
 import org.pgpainless.util.selection.keyring.PublicKeyRingSelectionStrategy;
 import org.pgpainless.util.selection.keyring.SecretKeyRingSelectionStrategy;
 
-public class Wildcard {
+public final class Wildcard {
+
+    private Wildcard() {
+
+    }
 
     public static class PubRingSelectionStrategy<O> extends PublicKeyRingSelectionStrategy<O> {
 
diff --git a/pgpainless-core/src/main/java/org/pgpainless/util/selection/keyring/impl/XMPP.java b/pgpainless-core/src/main/java/org/pgpainless/util/selection/keyring/impl/XMPP.java
index 31b46102..aafb0ad9 100644
--- a/pgpainless-core/src/main/java/org/pgpainless/util/selection/keyring/impl/XMPP.java
+++ b/pgpainless-core/src/main/java/org/pgpainless/util/selection/keyring/impl/XMPP.java
@@ -18,7 +18,11 @@ package org.pgpainless.util.selection.keyring.impl;
 import org.bouncycastle.openpgp.PGPPublicKeyRing;
 import org.bouncycastle.openpgp.PGPSecretKeyRing;
 
-public class XMPP {
+public final class XMPP {
+
+    private XMPP() {
+
+    }
 
     public static class PubRingSelectionStrategy extends ExactUserId.PubRingSelectionStrategy {