Add OpenPgpV4Fingerprint class

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

@@ -0,0 +1,129 @@
+/**
+ *
+ * Copyright 2018 Paul Schaub.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.jivesoftware.smackx.ox;
+
+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.util.encoders.Hex;
+
+/**
+ * This class represents an hex encoded, uppercase OpenPGP v4 fingerprint.
+ */
+public class OpenPgpV4Fingerprint implements CharSequence, Comparable<OpenPgpV4Fingerprint> {
+
+    private final String fingerprint;
+
+    /**
+     * Create an {@link OpenPgpV4Fingerprint}.
+     * @see <a href="https://xmpp.org/extensions/xep-0373.html#annoucning-pubkey">
+     *     XEP-0373 §4.1: The OpenPGP Public-Key Data Node about how to obtain the fingerprint</a>
+     * @param fingerprint hexadecimal representation of the fingerprint.
+     */
+    public OpenPgpV4Fingerprint(String fingerprint) throws PGPException {
+        String fp = Objects.requireNonNull(fingerprint)
+                .trim()
+                .toUpperCase();
+        if (!isValid(fp)) {
+            throw new PGPException("Fingerprint " + fingerprint +
+                    " does not appear to be a valid OpenPGP v4 fingerprint.");
+        }
+        this.fingerprint = fp;
+    }
+
+    public OpenPgpV4Fingerprint(byte[] bytes) throws PGPException {
+        this(new String(bytes, Charset.forName("UTF-8")));
+    }
+
+    public OpenPgpV4Fingerprint(PGPPublicKey key) throws PGPException {
+        this(Hex.encode(key.getFingerprint()));
+    }
+
+    /**
+     * Check, whether the fingerprint consists of 40 valid hexadecimal characters.
+     * @param fp fingerprint to check.
+     * @return true if fingerprint is valid.
+     */
+    private boolean isValid(String fp) {
+        return fp.matches("[0-9A-F]{40}");
+    }
+
+    /**
+     * Return the key id of the OpenPGP public key this {@link OpenPgpV4Fingerprint} belongs to.
+     *
+     * @see <a href="https://tools.ietf.org/html/rfc4880#section-12.2">
+     *     RFC-4880 §12.2: Key IDs and Fingerprints</a>
+     * @return key id
+     */
+    public long getKeyId() {
+        byte[] bytes = DatatypeConverter.parseHexBinary(this.toString());
+        byte[] lower8Bytes = Arrays.copyOfRange(bytes, 12, 20);
+        ByteBuffer byteBuffer = ByteBuffer.allocate(8);
+        byteBuffer.put(lower8Bytes);
+        byteBuffer.flip();
+        return byteBuffer.getLong();
+    }
+
+    @Override
+    public boolean equals(Object other) {
+        if (other == null) {
+            return false;
+        }
+
+        if (!(other instanceof CharSequence)) {
+            return false;
+        }
+
+        return this.toString().equals(other.toString());
+    }
+
+    @Override
+    public int hashCode() {
+        return fingerprint.hashCode();
+    }
+
+    @Override
+    public int length() {
+        return fingerprint.length();
+    }
+
+    @Override
+    public char charAt(int i) {
+        return fingerprint.charAt(i);
+    }
+
+    @Override
+    public CharSequence subSequence(int i, int i1) {
+        return fingerprint.subSequence(i, i1);
+    }
+
+    @Override
+    public String toString() {
+        return fingerprint;
+    }
+
+    @Override
+    public int compareTo(OpenPgpV4Fingerprint openPgpV4Fingerprint) {
+        return fingerprint.compareTo(openPgpV4Fingerprint.fingerprint);
+    }
+}