Allow for setting of expiration date during key generation

pgpainless-core/src/main/java/org/pgpainless/key/generation/KeyRingBuilder.java

@@ -66,6 +66,7 @@ public class KeyRingBuilder implements KeyRingBuilderInterface {
     private String userId;
     private final Set<String> additionalUserIds = new LinkedHashSet<>();
     private Passphrase passphrase;
+    private Date expirationDate = null;
 
     /**
      * Creates a simple, unencrypted RSA KeyPair of length {@code length} with user-id {@code userId}.
@@ -288,6 +289,16 @@ public class KeyRingBuilder implements KeyRingBuilderInterface {
 
     class WithAdditionalUserIdOrPassphraseImpl implements WithAdditionalUserIdOrPassphrase {
 
+        @Override
+        public WithAdditionalUserIdOrPassphrase setExpirationDate(@Nonnull Date expirationDate) {
+            Date now = new Date();
+            if (now.after(expirationDate)) {
+                throw new IllegalArgumentException("Expiration date must be in the future.");
+            }
+            KeyRingBuilder.this.expirationDate = expirationDate;
+            return this;
+        }
+
         @Override
         public WithAdditionalUserIdOrPassphrase withAdditionalUserId(@Nonnull String userId) {
             String trimmed = userId.trim();
@@ -341,6 +352,10 @@ public class KeyRingBuilder implements KeyRingBuilderInterface {
                 signatureGenerator = new PGPSignatureGenerator(signer);
                 PGPSignatureSubpacketGenerator hashedSubPacketGenerator = certKeySpec.getSubpacketGenerator();
                 hashedSubPacketGenerator.setPrimaryUserID(false, true);
+                if (expirationDate != null) {
+                    SignatureSubpacketGeneratorUtil.setExpirationDateInSubpacketGenerator(
+                            expirationDate, new Date(), hashedSubPacketGenerator);
+                }
                 PGPSignatureSubpacketVector hashedSubPackets = hashedSubPacketGenerator.generate();
 
                 // Generator which the user can get the key pair from

pgpainless-core/src/main/java/org/pgpainless/key/generation/KeyRingBuilderInterface.java

@@ -17,6 +17,7 @@ package org.pgpainless.key.generation;
 
 import java.security.InvalidAlgorithmParameterException;
 import java.security.NoSuchAlgorithmException;
+import java.util.Date;
 import javax.annotation.Nonnull;
 
 import org.bouncycastle.openpgp.PGPException;
@@ -60,6 +61,14 @@ public interface KeyRingBuilderInterface {
             return withAdditionalUserId(userId.toString());
         }
 
+        /**
+         * Set an expiration date for the key.
+         *
+         * @param expirationDate date on which the key will expire.
+         * @return builder
+         */
+        WithAdditionalUserIdOrPassphrase setExpirationDate(@Nonnull Date expirationDate);
+
         WithAdditionalUserIdOrPassphrase withAdditionalUserId(@Nonnull String userId);
 
         WithAdditionalUserIdOrPassphrase withAdditionalUserId(@Nonnull byte[] userId);

pgpainless-core/src/test/java/org/pgpainless/key/generation/GenerateKeyWithAdditionalUserIdTest.java

@@ -22,6 +22,7 @@ import java.io.ByteArrayOutputStream;
 import java.io.IOException;
 import java.security.InvalidAlgorithmParameterException;
 import java.security.NoSuchAlgorithmException;
+import java.util.Date;
 import java.util.Iterator;
 
 import org.bouncycastle.bcpg.ArmoredOutputStream;
@@ -39,6 +40,8 @@ public class GenerateKeyWithAdditionalUserIdTest {
 
     @Test
     public void test() throws InvalidAlgorithmParameterException, NoSuchAlgorithmException, PGPException, IOException {
+        Date now = new Date();
+        Date expiration = new Date(now.getTime() + 1000 * 5);
         PGPSecretKeyRing secretKeys = PGPainless.generateKeyRing()
                 .withPrimaryKey(KeySpec.getBuilder(KeyType.RSA(RsaLength._3072))
                         .withKeyFlags(KeyFlag.CERTIFY_OTHER, KeyFlag.SIGN_DATA, KeyFlag.ENCRYPT_COMMS)
@@ -47,10 +50,13 @@ public class GenerateKeyWithAdditionalUserIdTest {
                 .withAdditionalUserId("additional@user.id")
                 .withAdditionalUserId("additional2@user.id")
                 .withAdditionalUserId("\ttrimThis@user.id     ")
+                .setExpirationDate(expiration)
                 .withoutPassphrase()
                 .build();
         PGPPublicKeyRing publicKeys = KeyRingUtils.publicKeyRingFrom(secretKeys);
 
+        assertEquals(expiration.getTime(), PGPainless.inspectKeyRing(publicKeys).getExpirationDate().getTime(), 2);
+
         Iterator<String> userIds = publicKeys.getPublicKey().getUserIDs();
         assertEquals("primary@user.id", userIds.next());
         assertEquals("additional@user.id", userIds.next());