Add support for generating keys without user-ids

Fixes #296

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

@@ -143,9 +143,6 @@ public class KeyRingBuilder implements KeyRingBuilderInterface<KeyRingBuilder> {
     @Override
     public PGPSecretKeyRing build() throws NoSuchAlgorithmException, PGPException,
             InvalidAlgorithmParameterException {
-        if (userIds.isEmpty()) {
-            throw new IllegalStateException("At least one user-id is required.");
-        }
         PGPDigestCalculator keyFingerprintCalculator = ImplementationFactory.getInstance().getV4FingerprintCalculator();
         PBESecretKeyEncryptor secretKeyEncryptor = buildSecretKeyEncryptor(keyFingerprintCalculator);
         PBESecretKeyDecryptor secretKeyDecryptor = buildSecretKeyDecryptor();
@@ -157,19 +154,35 @@ public class KeyRingBuilder implements KeyRingBuilderInterface<KeyRingBuilder> {
         PGPContentSignerBuilder signer = buildContentSigner(certKey);
         PGPSignatureGenerator signatureGenerator = new PGPSignatureGenerator(signer);
 
-        // Prepare primary user-id sig
         SignatureSubpackets hashedSubPacketGenerator = primaryKeySpec.getSubpacketGenerator();
         hashedSubPacketGenerator.setIssuerFingerprintAndKeyId(certKey.getPublicKey());
-        hashedSubPacketGenerator.setPrimaryUserId();
         if (expirationDate != null) {
             hashedSubPacketGenerator.setKeyExpirationTime(certKey.getPublicKey(), expirationDate);
         }
+        if (!userIds.isEmpty()) {
+            hashedSubPacketGenerator.setPrimaryUserId();
+        }
+
         PGPSignatureSubpacketGenerator generator = new PGPSignatureSubpacketGenerator();
         SignatureSubpacketsHelper.applyTo(hashedSubPacketGenerator, generator);
         PGPSignatureSubpacketVector hashedSubPackets = generator.generate();
+        PGPKeyRingGenerator ringGenerator;
+        if (userIds.isEmpty()) {
+            ringGenerator = new PGPKeyRingGenerator(
+                    certKey,
+                    keyFingerprintCalculator,
+                    hashedSubPackets,
+                    null,
+                    signer,
+                    secretKeyEncryptor);
+        } else {
+            String primaryUserId = userIds.entrySet().iterator().next().getKey();
+            ringGenerator = new PGPKeyRingGenerator(
+                    SignatureType.POSITIVE_CERTIFICATION.getCode(), certKey,
+                    primaryUserId, keyFingerprintCalculator,
+                    hashedSubPackets, null, signer, secretKeyEncryptor);
+        }
 
-        PGPKeyRingGenerator ringGenerator = buildRingGenerator(
-                certKey, signer, keyFingerprintCalculator, hashedSubPackets, secretKeyEncryptor);
         addSubKeys(certKey, ringGenerator);
 
         // Generate secret key ring with only primary user id
@@ -182,7 +195,9 @@ public class KeyRingBuilder implements KeyRingBuilderInterface<KeyRingBuilder> {
         PGPPrivateKey privateKey = UnlockSecretKey.unlockSecretKey(secretKeyRing.getSecretKey(), secretKeyDecryptor);
         Iterator<Map.Entry<String, SelfSignatureSubpackets.Callback>> userIdIterator =
                 this.userIds.entrySet().iterator();
-        userIdIterator.next(); // Skip primary user id
+        if (userIdIterator.hasNext()) {
+            userIdIterator.next(); // Skip primary user id
+        }
         while (userIdIterator.hasNext()) {
             Map.Entry<String, SelfSignatureSubpackets.Callback> additionalUserId = userIdIterator.next();
             String userIdString = additionalUserId.getKey();
@@ -217,19 +232,6 @@ public class KeyRingBuilder implements KeyRingBuilderInterface<KeyRingBuilder> {
         return secretKeyRing;
     }
 
-    private PGPKeyRingGenerator buildRingGenerator(PGPKeyPair certKey,
-                                                   PGPContentSignerBuilder signer,
-                                                   PGPDigestCalculator keyFingerprintCalculator,
-                                                   PGPSignatureSubpacketVector hashedSubPackets,
-                                                   PBESecretKeyEncryptor secretKeyEncryptor)
-            throws PGPException {
-        String primaryUserId = userIds.entrySet().iterator().next().getKey();
-        return new PGPKeyRingGenerator(
-                SignatureType.POSITIVE_CERTIFICATION.getCode(), certKey,
-                primaryUserId, keyFingerprintCalculator,
-                hashedSubPackets, null, signer, secretKeyEncryptor);
-    }
-
     private void addSubKeys(PGPKeyPair primaryKey, PGPKeyRingGenerator ringGenerator)
             throws NoSuchAlgorithmException, PGPException, InvalidAlgorithmParameterException {
         for (KeySpec subKeySpec : subkeySpecs) {

pgpainless-core/src/main/java/org/pgpainless/signature/consumer/CertificateValidator.java

@@ -138,6 +138,7 @@ public final class CertificateValidator {
         }
 
         boolean anyUserIdValid = false;
+        boolean hasAnyUserIds = !userIdSignatures.keySet().isEmpty();
         for (String userId : userIdSignatures.keySet()) {
             if (!userIdSignatures.get(userId).isEmpty()) {
                 PGPSignature current = userIdSignatures.get(userId).get(0);
@@ -149,7 +150,7 @@ public final class CertificateValidator {
             }
         }
 
-        if (!anyUserIdValid) {
+        if (hasAnyUserIds && !anyUserIdValid) {
             throw new SignatureValidationException("No valid user-id found.", rejections);
         }
 

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

@@ -0,0 +1,93 @@
+// SPDX-FileCopyrightText: 2022 Paul Schaub <vanitasvitae@fsfe.org>
+//
+// SPDX-License-Identifier: Apache-2.0
+
+package org.pgpainless.key.generation;
+
+import org.bouncycastle.openpgp.PGPException;
+import org.bouncycastle.openpgp.PGPPublicKeyRing;
+import org.bouncycastle.openpgp.PGPSecretKeyRing;
+import org.bouncycastle.util.io.Streams;
+import org.junit.JUtils;
+import org.junit.jupiter.api.Test;
+import org.pgpainless.PGPainless;
+import org.pgpainless.algorithm.KeyFlag;
+import org.pgpainless.decryption_verification.ConsumerOptions;
+import org.pgpainless.decryption_verification.DecryptionStream;
+import org.pgpainless.decryption_verification.OpenPgpMetadata;
+import org.pgpainless.encryption_signing.EncryptionOptions;
+import org.pgpainless.encryption_signing.EncryptionResult;
+import org.pgpainless.encryption_signing.EncryptionStream;
+import org.pgpainless.encryption_signing.ProducerOptions;
+import org.pgpainless.encryption_signing.SigningOptions;
+import org.pgpainless.key.generation.type.KeyType;
+import org.pgpainless.key.generation.type.eddsa.EdDSACurve;
+import org.pgpainless.key.generation.type.xdh.XDHSpec;
+import org.pgpainless.key.info.KeyRingInfo;
+import org.pgpainless.key.protection.SecretKeyRingProtector;
+import org.pgpainless.util.DateUtil;
+
+import java.io.ByteArrayInputStream;
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.security.InvalidAlgorithmParameterException;
+import java.security.NoSuchAlgorithmException;
+import java.util.Date;
+
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+public class GenerateKeyWithoutUserIdTest {
+
+    @Test
+    public void generateKeyWithoutUserId() throws PGPException, InvalidAlgorithmParameterException, NoSuchAlgorithmException, IOException {
+        Date expirationDate = DateUtil.toSecondsPrecision(new Date(DateUtil.now().getTime() + 1000 * 6000));
+        PGPSecretKeyRing secretKey = PGPainless.buildKeyRing()
+                .setPrimaryKey(KeySpec.getBuilder(KeyType.EDDSA(EdDSACurve._Ed25519), KeyFlag.CERTIFY_OTHER))
+                .addSubkey(KeySpec.getBuilder(KeyType.EDDSA(EdDSACurve._Ed25519), KeyFlag.SIGN_DATA))
+                .addSubkey(KeySpec.getBuilder(KeyType.XDH(XDHSpec._X25519), KeyFlag.ENCRYPT_COMMS, KeyFlag.ENCRYPT_STORAGE))
+                .setExpirationDate(expirationDate)
+                .build();
+
+        KeyRingInfo info = PGPainless.inspectKeyRing(secretKey);
+        assertNull(info.getPrimaryUserId());
+        assertTrue(info.getUserIds().isEmpty());
+        JUtils.assertDateEquals(expirationDate, info.getPrimaryKeyExpirationDate());
+
+        InputStream plaintextIn = new ByteArrayInputStream("Hello, World!\n".getBytes());
+        ByteArrayOutputStream ciphertextOut = new ByteArrayOutputStream();
+        SecretKeyRingProtector protector = SecretKeyRingProtector.unprotectedKeys();
+        PGPPublicKeyRing certificate = PGPainless.extractCertificate(secretKey);
+
+        EncryptionStream encryptionStream = PGPainless.encryptAndOrSign()
+                .onOutputStream(ciphertextOut)
+                .withOptions(ProducerOptions.signAndEncrypt(
+                        EncryptionOptions.get()
+                                .addRecipient(certificate),
+                        SigningOptions.get()
+                                .addSignature(protector, secretKey)
+                ));
+        Streams.pipeAll(plaintextIn, encryptionStream);
+        encryptionStream.close();
+
+        EncryptionResult result = encryptionStream.getResult();
+        assertTrue(result.isEncryptedFor(certificate));
+
+        ByteArrayInputStream ciphertextIn = new ByteArrayInputStream(ciphertextOut.toByteArray());
+        ByteArrayOutputStream plaintextOut = new ByteArrayOutputStream();
+        DecryptionStream decryptionStream = PGPainless.decryptAndOrVerify()
+                .onInputStream(ciphertextIn)
+                .withOptions(ConsumerOptions.get()
+                        .addDecryptionKey(secretKey)
+                        .addVerificationCert(certificate));
+
+        Streams.pipeAll(decryptionStream, plaintextOut);
+        decryptionStream.close();
+
+        OpenPgpMetadata metadata = decryptionStream.getResult();
+
+        assertTrue(metadata.containsVerifiedSignatureFrom(certificate));
+        assertTrue(metadata.isEncrypted());
+    }
+}