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 10258606..555a3369 100644
--- a/pgpainless-core/src/main/java/org/pgpainless/util/ArmorUtils.java
+++ b/pgpainless-core/src/main/java/org/pgpainless/util/ArmorUtils.java
@@ -22,6 +22,7 @@ import java.io.InputStream;
 import java.util.ArrayList;
 import java.util.Iterator;
 import java.util.List;
+import java.util.regex.Pattern;
 
 import org.bouncycastle.bcpg.ArmoredInputStream;
 import org.bouncycastle.bcpg.ArmoredOutputStream;
@@ -34,6 +35,9 @@ import org.pgpainless.key.OpenPgpV4Fingerprint;
 
 public class ArmorUtils {
 
+    // MessageIDs are 32 printable characters
+    private static final Pattern PATTERN_MESSAGE_ID = Pattern.compile("^\\S{32}$");
+
     public static final String HEADER_COMMENT = "Comment";
     public static final String HEADER_VERSION = "Version";
     public static final String HEADER_MESSAGEID = "MessageID";
@@ -74,6 +78,24 @@ public class ArmorUtils {
         return toAsciiArmoredString(inputStream, null);
     }
 
+    public static void addHashAlgorithmHeader(ArmoredOutputStream armor, HashAlgorithm hashAlgorithm) {
+        armor.addHeader(HEADER_HASH, hashAlgorithm.getAlgorithmName());
+    }
+
+    public static void addCommentHeader(ArmoredOutputStream armor, String comment) {
+        armor.addHeader(HEADER_COMMENT, comment);
+    }
+
+    public static void addMessageIdHeader(ArmoredOutputStream armor, String messageId) {
+        if (messageId == null) {
+            throw new NullPointerException("MessageID cannot be null.");
+        }
+        if (!PATTERN_MESSAGE_ID.matcher(messageId).matches()) {
+            throw new IllegalArgumentException("MessageIDs MUST consist of 32 printable characters.");
+        }
+        armor.addHeader(HEADER_MESSAGEID, messageId);
+    }
+
     public static String toAsciiArmoredString(InputStream inputStream, MultiMap<String, String> additionalHeaderValues) throws IOException {
         ByteArrayOutputStream out = new ByteArrayOutputStream();
         ArmoredOutputStream armor = ArmoredOutputStreamFactory.get(out);
@@ -104,9 +126,12 @@ public class ArmorUtils {
 
     public static List<HashAlgorithm> getHashAlgorithms(ArmoredInputStream armor) {
         List<String> algorithmNames = getHashHeaderValues(armor);
-        List<HashAlgorithm> algorithms = new ArrayList<>(algorithmNames.size());
+        List<HashAlgorithm> algorithms = new ArrayList<>();
         for (String name : algorithmNames) {
-            algorithms.add(HashAlgorithm.fromName(name));
+            HashAlgorithm algorithm = HashAlgorithm.fromName(name);
+            if (algorithm != null) {
+                algorithms.add(algorithm);
+            }
         }
         return algorithms;
     }
diff --git a/pgpainless-core/src/test/java/org/pgpainless/util/ArmorUtilsTest.java b/pgpainless-core/src/test/java/org/pgpainless/util/ArmorUtilsTest.java
index cd030bf2..e254dea7 100644
--- a/pgpainless-core/src/test/java/org/pgpainless/util/ArmorUtilsTest.java
+++ b/pgpainless-core/src/test/java/org/pgpainless/util/ArmorUtilsTest.java
@@ -16,13 +16,16 @@
 package org.pgpainless.util;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
 
 import java.io.ByteArrayInputStream;
+import java.io.ByteArrayOutputStream;
 import java.io.IOException;
 import java.nio.charset.StandardCharsets;
 import java.util.List;
 
 import org.bouncycastle.bcpg.ArmoredInputStream;
+import org.bouncycastle.bcpg.ArmoredOutputStream;
 import org.junit.jupiter.api.Test;
 import org.pgpainless.algorithm.HashAlgorithm;
 
@@ -74,4 +77,16 @@ public class ArmorUtilsTest {
         // MessageID
         assertEquals(0, ArmorUtils.getMessageIdHeaderValues(armorIn).size());
     }
+
+    @Test
+    public void testSetMessageId() {
+        ArmoredOutputStream armor = new ArmoredOutputStream(new ByteArrayOutputStream());
+        ArmorUtils.addMessageIdHeader(armor, "abcdefghi01234567890123456789012");
+
+        assertThrows(NullPointerException.class, () -> ArmorUtils.addMessageIdHeader(armor, null));
+        assertThrows(IllegalArgumentException.class, () -> ArmorUtils.addMessageIdHeader(armor, "tooShort"));
+        assertThrows(IllegalArgumentException.class, () -> ArmorUtils.addMessageIdHeader(armor, "toLooooooooooooooooooooooooooooooooooong"));
+        assertThrows(IllegalArgumentException.class, () -> ArmorUtils.addMessageIdHeader(armor, "contains spaces 7890123456789012"));
+        assertThrows(IllegalArgumentException.class, () -> ArmorUtils.addMessageIdHeader(armor, "contains\nnewlines\n12345678901234"));
+    }
 }