Improve OpenPgpV4Fingerprint and decryption API

src/main/java/org/pgpainless/pgpainless/decryption_verification/DecryptionBuilder.java

@@ -25,6 +25,7 @@ import org.bouncycastle.openpgp.PGPException;
 import org.bouncycastle.openpgp.PGPPublicKeyRing;
 import org.bouncycastle.openpgp.PGPPublicKeyRingCollection;
 import org.bouncycastle.openpgp.PGPSecretKeyRingCollection;
+import org.pgpainless.pgpainless.key.OpenPgpV4Fingerprint;
 import org.pgpainless.pgpainless.key.protection.SecretKeyRingProtector;
 
 public class DecryptionBuilder implements DecryptionBuilderInterface {
@@ -61,12 +62,18 @@ public class DecryptionBuilder implements DecryptionBuilderInterface {
     class VerifyWithImpl implements VerifyWith {
 
         @Override
-        public HandleMissingPublicKeys verifyWith(Set<Long> trustedKeyIds,
+        public HandleMissingPublicKeys verifyWith(Set<OpenPgpV4Fingerprint> trustedKeyIds,
                                                   PGPPublicKeyRingCollection publicKeyRingCollection) {
             Set<PGPPublicKeyRing> publicKeyRings = new HashSet<>();
             for (Iterator<PGPPublicKeyRing> i = publicKeyRingCollection.getKeyRings(); i.hasNext(); ) {
                 PGPPublicKeyRing p = i.next();
-                if (trustedKeyIds.contains(p.getPublicKey().getKeyID())) {
+                OpenPgpV4Fingerprint fingerprint;
+                try {
+                    fingerprint = new OpenPgpV4Fingerprint(p);
+                } catch (PGPException e) {
+                    throw new IllegalArgumentException(e);
+                }
+                if (trustedKeyIds.contains(fingerprint)) {
                     publicKeyRings.add(p);
                 }
             }
@@ -89,7 +96,7 @@ public class DecryptionBuilder implements DecryptionBuilderInterface {
     class HandleMissingPublicKeysImpl implements HandleMissingPublicKeys {
 
         @Override
-        public Build handleMissingPublicKeysWith(org.pgpainless.pgpainless.decryption_verification.MissingPublicKeyCallback callback) {
+        public Build handleMissingPublicKeysWith(MissingPublicKeyCallback callback) {
             DecryptionBuilder.this.missingPublicKeyCallback = callback;
             return new BuildImpl();
         }

src/main/java/org/pgpainless/pgpainless/decryption_verification/DecryptionBuilderInterface.java

@@ -23,6 +23,7 @@ import org.bouncycastle.openpgp.PGPException;
 import org.bouncycastle.openpgp.PGPPublicKeyRing;
 import org.bouncycastle.openpgp.PGPPublicKeyRingCollection;
 import org.bouncycastle.openpgp.PGPSecretKeyRingCollection;
+import org.pgpainless.pgpainless.key.OpenPgpV4Fingerprint;
 import org.pgpainless.pgpainless.key.protection.SecretKeyRingProtector;
 
 public interface DecryptionBuilderInterface {
@@ -39,7 +40,7 @@ public interface DecryptionBuilderInterface {
 
     interface VerifyWith {
 
-        HandleMissingPublicKeys verifyWith(Set<Long> trustedFingerprints, PGPPublicKeyRingCollection publicKeyRings);
+        HandleMissingPublicKeys verifyWith(Set<OpenPgpV4Fingerprint> trustedFingerprints, PGPPublicKeyRingCollection publicKeyRings);
 
         HandleMissingPublicKeys verifyWith(Set<PGPPublicKeyRing> publicKeyRings);
 
@@ -49,7 +50,7 @@ public interface DecryptionBuilderInterface {
 
     interface HandleMissingPublicKeys {
 
-        Build handleMissingPublicKeysWith(org.pgpainless.pgpainless.decryption_verification.MissingPublicKeyCallback callback);
+        Build handleMissingPublicKeysWith(MissingPublicKeyCallback callback);
 
         Build ignoreMissingPublicKeys();
     }

src/main/java/org/pgpainless/pgpainless/key/OpenPgpV4Fingerprint.java

@@ -14,17 +14,18 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-package org.jivesoftware.smackx.ox;
+package org.pgpainless.pgpainless.key;
 
 import javax.xml.bind.DatatypeConverter;
 import java.nio.ByteBuffer;
 import java.nio.charset.Charset;
 import java.util.Arrays;
 
-import org.jivesoftware.smack.util.Objects;
-
 import org.bouncycastle.openpgp.PGPException;
 import org.bouncycastle.openpgp.PGPPublicKey;
+import org.bouncycastle.openpgp.PGPPublicKeyRing;
+import org.bouncycastle.openpgp.PGPSecretKey;
+import org.bouncycastle.openpgp.PGPSecretKeyRing;
 import org.bouncycastle.util.encoders.Hex;
 
 /**
@@ -41,9 +42,10 @@ public class OpenPgpV4Fingerprint implements CharSequence, Comparable<OpenPgpV4F
      * @param fingerprint hexadecimal representation of the fingerprint.
      */
     public OpenPgpV4Fingerprint(String fingerprint) throws PGPException {
-        String fp = Objects.requireNonNull(fingerprint)
+        if (fingerprint == null) {
-                .trim()
+            throw new NullPointerException("Fingerprint MUST NOT be null.");
-                .toUpperCase();
+        }
+        String fp = fingerprint.trim().toUpperCase();
         if (!isValid(fp)) {
             throw new PGPException("Fingerprint " + fingerprint +
                     " does not appear to be a valid OpenPGP v4 fingerprint.");
@@ -57,6 +59,21 @@ public class OpenPgpV4Fingerprint implements CharSequence, Comparable<OpenPgpV4F
 
     public OpenPgpV4Fingerprint(PGPPublicKey key) throws PGPException {
         this(Hex.encode(key.getFingerprint()));
+        if (key.getVersion() != 4) {
+            throw new PGPException("Key is not a v4 OpenPgp key.");
+        }
+    }
+
+    public OpenPgpV4Fingerprint(PGPSecretKey key) throws PGPException {
+        this(key.getPublicKey());
+    }
+
+    public OpenPgpV4Fingerprint(PGPPublicKeyRing ring) throws PGPException {
+        this(ring.getPublicKey());
+    }
+
+    public OpenPgpV4Fingerprint(PGPSecretKeyRing ring) throws PGPException {
+        this(ring.getPublicKey());
     }
 
     /**