Add support for creating detached revocation certificates

pgpainless-core/src/main/java/org/pgpainless/key/modification/secretkeyring/SecretKeyRingEditor.java

@@ -38,6 +38,8 @@ import org.bouncycastle.openpgp.PGPSecretKey;
 import org.bouncycastle.openpgp.PGPSecretKeyRing;
 import org.bouncycastle.openpgp.PGPSignature;
 import org.bouncycastle.openpgp.PGPSignatureGenerator;
+import org.bouncycastle.openpgp.PGPSignatureSubpacketGenerator;
+import org.bouncycastle.openpgp.PGPSignatureSubpacketVector;
 import org.bouncycastle.openpgp.operator.PBESecretKeyDecryptor;
 import org.bouncycastle.openpgp.operator.PBESecretKeyEncryptor;
 import org.bouncycastle.openpgp.operator.PGPContentSignerBuilder;
@@ -58,6 +60,7 @@ import org.pgpainless.key.protection.SecretKeyRingProtector;
 import org.pgpainless.key.protection.UnprotectedKeysProtector;
 import org.pgpainless.key.protection.passphrase_provider.SolitaryPassphraseProvider;
 import org.pgpainless.key.util.KeyRingUtils;
+import org.pgpainless.key.util.RevocationAttributes;
 import org.pgpainless.key.util.SignatureUtils;
 import org.pgpainless.util.Passphrase;
 
@@ -271,14 +274,37 @@ public class SecretKeyRingEditor implements SecretKeyRingEditorInterface {
         return this;
     }
 
-    private PGPSecretKeyRing revokeSubKey(SecretKeyRingProtector protector, PGPPublicKey revokeeSubKey) throws PGPException {
-        PGPSecretKey primaryKey = secretKeyRing.getSecretKey();
-        PGPSignatureGenerator signatureGenerator = SignatureUtils.getSignatureGeneratorFor(primaryKey);
-        PGPPrivateKey privateKey = primaryKey.extractPrivateKey(protector.getDecryptor(primaryKey.getKeyID()));
-        signatureGenerator.init(SignatureType.SUBKEY_REVOCATION.getCode(), privateKey);
+    @Override
+    public PGPSignature createRevocationCertificate(OpenPgpV4Fingerprint fingerprint,
+                                                    SecretKeyRingProtector secretKeyRingProtector,
+                                                    RevocationAttributes revocationAttributes)
+            throws PGPException {
+        PGPPublicKey revokeeSubKey = secretKeyRing.getPublicKey(fingerprint.getKeyId());
+        if (revokeeSubKey == null) {
+            throw new NoSuchElementException("No subkey with fingerprint " + fingerprint + " found.");
+        }
 
-        // Generate revocation
-        PGPSignature subKeyRevocation = signatureGenerator.generateCertification(primaryKey.getPublicKey(), revokeeSubKey);
+        PGPSignature revocationCertificate = generateRevocation(secretKeyRingProtector, revokeeSubKey, revocationAttributes);
+        return revocationCertificate;
+    }
+
+    @Override
+    public PGPSignature createRevocationCertificate(long subKeyId,
+                                                    SecretKeyRingProtector secretKeyRingProtector,
+                                                    RevocationAttributes revocationAttributes)
+            throws PGPException {
+        PGPPublicKey revokeeSubKey = secretKeyRing.getPublicKey(subKeyId);
+        if (revokeeSubKey == null) {
+            throw new NoSuchElementException("No subkey with id " + Long.toHexString(subKeyId) + " found.");
+        }
+
+        PGPSignature revocationCertificate = generateRevocation(secretKeyRingProtector, revokeeSubKey, revocationAttributes);
+        return revocationCertificate;
+    }
+
+    private PGPSecretKeyRing revokeSubKey(SecretKeyRingProtector protector, PGPPublicKey revokeeSubKey)
+            throws PGPException {
+        PGPSignature subKeyRevocation = generateRevocation(protector, revokeeSubKey, null);
         revokeeSubKey = PGPPublicKey.addCertification(revokeeSubKey, subKeyRevocation);
 
         // Inject revoked public key into key ring
@@ -287,6 +313,31 @@ public class SecretKeyRingEditor implements SecretKeyRingEditorInterface {
         return PGPSecretKeyRing.replacePublicKeys(secretKeyRing, publicKeyRing);
     }
 
+    private PGPSignature generateRevocation(SecretKeyRingProtector protector,
+                                            PGPPublicKey revokeeSubKey,
+                                            RevocationAttributes revocationAttributes)
+            throws PGPException {
+        PGPSecretKey primaryKey = secretKeyRing.getSecretKey();
+        PGPSignatureGenerator signatureGenerator = SignatureUtils.getSignatureGeneratorFor(primaryKey);
+        PGPSignatureSubpacketGenerator subpacketGenerator = new PGPSignatureSubpacketGenerator();
+        subpacketGenerator.setIssuerFingerprint(false, primaryKey);
+
+        if (revocationAttributes != null) {
+            subpacketGenerator.setRevocationReason(false, revocationAttributes.getReason().code(), revocationAttributes.getDescription());
+        }
+
+        PGPSignatureSubpacketVector subPackets = subpacketGenerator.generate();
+        signatureGenerator.setHashedSubpackets(subPackets);
+
+        PGPPrivateKey privateKey = primaryKey.extractPrivateKey(protector.getDecryptor(primaryKey.getKeyID()));
+        SignatureType type = revokeeSubKey.isMasterKey() ? SignatureType.KEY_REVOCATION : SignatureType.SUBKEY_REVOCATION;
+        signatureGenerator.init(type.getCode(), privateKey);
+
+        // Generate revocation
+        PGPSignature subKeyRevocation = signatureGenerator.generateCertification(primaryKey.getPublicKey(), revokeeSubKey);
+        return subKeyRevocation;
+    }
+
     @Override
     public WithKeyRingEncryptionSettings changePassphraseFromOldPassphrase(@Nullable Passphrase oldPassphrase,
                                                                            @Nonnull KeyRingProtectionSettings oldProtectionSettings) {

pgpainless-core/src/main/java/org/pgpainless/key/modification/secretkeyring/SecretKeyRingEditorInterface.java

@@ -23,10 +23,12 @@ import javax.annotation.Nullable;
 import org.bouncycastle.openpgp.PGPException;
 import org.bouncycastle.openpgp.PGPSecretKey;
 import org.bouncycastle.openpgp.PGPSecretKeyRing;
+import org.bouncycastle.openpgp.PGPSignature;
 import org.pgpainless.key.OpenPgpV4Fingerprint;
 import org.pgpainless.key.generation.KeySpec;
 import org.pgpainless.key.protection.KeyRingProtectionSettings;
 import org.pgpainless.key.protection.SecretKeyRingProtector;
+import org.pgpainless.key.util.RevocationAttributes;
 import org.pgpainless.key.util.UserId;
 import org.pgpainless.util.Passphrase;
 
@@ -127,6 +129,16 @@ public interface SecretKeyRingEditorInterface {
      */
     SecretKeyRingEditorInterface revokeSubKey(long subKeyId, SecretKeyRingProtector secretKeyRingProtector) throws PGPException;
 
+    PGPSignature createRevocationCertificate(OpenPgpV4Fingerprint fingerprint,
+                                             SecretKeyRingProtector secretKeyRingProtector,
+                                             RevocationAttributes revocationAttributes)
+            throws PGPException;
+
+    PGPSignature createRevocationCertificate(long subKeyId,
+                                             SecretKeyRingProtector secretKeyRingProtector,
+                                             RevocationAttributes revocationAttributes)
+            throws PGPException;
+
     /**
      * Change the passphrase of the whole key ring.
      *

pgpainless-core/src/main/java/org/pgpainless/key/util/RevocationAttributes.java

@@ -0,0 +1,116 @@
+/*
+ * Copyright 2020 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.pgpainless.key.util;
+
+public final class RevocationAttributes {
+
+    public enum Reason {
+        NO_REASON((byte) 0),
+        KEY_SUPERSEDED((byte) 1),
+        KEY_COMPROMISED((byte) 2),
+        KEY_RETIRED((byte) 3),
+        USER_ID_NO_LONGER_VALID((byte) 32),
+        ;
+
+        private final byte reasonCode;
+
+        Reason(byte reasonCode) {
+            this.reasonCode = reasonCode;
+        }
+
+        public byte code() {
+            return reasonCode;
+        }
+
+
+        @Override
+        public String toString() {
+            return code() + " - " + name();
+        }
+    }
+
+    public enum RevocationType {
+        KEY_REVOCATION,
+        CERT_REVOCATION
+    }
+
+    private final Reason reason;
+    private final String description;
+
+    private RevocationAttributes(Reason reason, String description) {
+        this.reason = reason;
+        this.description = description;
+    }
+
+    public Reason getReason() {
+        return reason;
+    }
+
+    public String getDescription() {
+        return description;
+    }
+
+    public static WithReason createKeyRevocation() {
+        return new WithReason(RevocationType.KEY_REVOCATION);
+    }
+
+    public static WithReason createCertificateRevocation() {
+        return new WithReason(RevocationType.CERT_REVOCATION);
+    }
+
+    public static final class WithReason {
+
+        private final RevocationType type;
+
+        private WithReason(RevocationType type) {
+            this.type = type;
+        }
+
+        public WithDescription withReason(Reason reason) {
+            throwIfReasonTypeMismatch(reason, type);
+            return new WithDescription(reason);
+        }
+
+        private void throwIfReasonTypeMismatch(Reason reason, RevocationType type) {
+            if (type == RevocationType.KEY_REVOCATION) {
+                if (reason == Reason.USER_ID_NO_LONGER_VALID) {
+                    throw new IllegalArgumentException("Reason " + reason + " can only be used for certificate revocations, not to revoke keys.");
+                }
+            } else if (type == RevocationType.CERT_REVOCATION) {
+                switch (reason) {
+                    case KEY_SUPERSEDED:
+                    case KEY_COMPROMISED:
+                    case KEY_RETIRED:
+                        throw new IllegalArgumentException("Reason " + reason + " can only be used for key revocations, not to revoke certificates.");
+                }
+            }
+        }
+
+    }
+
+    public static final class WithDescription {
+
+        private final Reason reason;
+
+        private WithDescription(Reason reason) {
+            this.reason = reason;
+        }
+
+        public RevocationAttributes withDescription(String description) {
+            return new RevocationAttributes(reason, description);
+        }
+    }
+}

pgpainless-core/src/main/java/org/pgpainless/util/ArmorUtils.java

@@ -25,7 +25,7 @@ import org.bouncycastle.openpgp.PGPPublicKeyRing;
 import org.bouncycastle.openpgp.PGPSecretKeyRing;
 import org.bouncycastle.util.io.Streams;
 
-public class KeyPrinter {
+public class ArmorUtils {
 
     public static String toAsciiArmoredString(PGPSecretKeyRing secretKeys) throws IOException {
         return toAsciiArmoredString(secretKeys.getEncoded());

pgpainless-core/src/test/java/org/pgpainless/key/modification/RevokeSubKeyTest.java

@@ -15,6 +15,7 @@
  */
 package org.pgpainless.key.modification;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
@@ -22,14 +23,20 @@ import java.io.IOException;
 import java.util.Iterator;
 
 import org.bouncycastle.openpgp.PGPException;
+import org.bouncycastle.openpgp.PGPPublicKey;
 import org.bouncycastle.openpgp.PGPSecretKey;
 import org.bouncycastle.openpgp.PGPSecretKeyRing;
+import org.bouncycastle.openpgp.PGPSignature;
 import org.junit.jupiter.api.Test;
 import org.pgpainless.PGPainless;
+import org.pgpainless.algorithm.SignatureType;
 import org.pgpainless.key.OpenPgpV4Fingerprint;
 import org.pgpainless.key.TestKeys;
+import org.pgpainless.key.modification.secretkeyring.SecretKeyRingEditorInterface;
 import org.pgpainless.key.protection.PasswordBasedSecretKeyRingProtector;
 import org.pgpainless.key.protection.SecretKeyRingProtector;
+import org.pgpainless.key.util.RevocationAttributes;
+import org.pgpainless.util.ArmorUtils;
 import org.pgpainless.util.Passphrase;
 
 public class RevokeSubKeyTest {
@@ -56,4 +63,45 @@ public class RevokeSubKeyTest {
 
         assertTrue(subKey.getPublicKey().hasRevocation());
     }
+
+    @Test
+    public void detachedRevokeSubkeyTest() throws IOException, PGPException {
+        PGPSecretKeyRing secretKeys = TestKeys.getCryptieSecretKeyRing();
+        OpenPgpV4Fingerprint fingerprint = new OpenPgpV4Fingerprint(secretKeys);
+        SecretKeyRingProtector protector = PasswordBasedSecretKeyRingProtector.forKey(secretKeys, Passphrase.fromPassword("password123"));
+
+        PGPSignature revocationCertificate = PGPainless.modifyKeyRing(secretKeys)
+                .createRevocationCertificate(fingerprint, protector, RevocationAttributes.createKeyRevocation()
+                        .withReason(RevocationAttributes.Reason.KEY_RETIRED)
+                        .withDescription("Key no longer used."));
+
+        // CHECKSTYLE:OFF
+        System.out.println("Revocation Certificate:");
+        System.out.println(ArmorUtils.toAsciiArmoredString(revocationCertificate.getEncoded()));
+        // CHECKSTYLE:ON
+
+        PGPPublicKey publicKey = secretKeys.getPublicKey();
+        assertFalse(publicKey.hasRevocation());
+
+        publicKey = PGPPublicKey.addCertification(publicKey, revocationCertificate);
+
+        assertTrue(publicKey.hasRevocation());
+    }
+
+    @Test
+    public void testRevocationSignatureTypeCorrect() throws IOException, PGPException {
+        PGPSecretKeyRing secretKeys = TestKeys.getCryptieSecretKeyRing();
+        Iterator<PGPPublicKey> keysIterator = secretKeys.getPublicKeys();
+        PGPPublicKey primaryKey = keysIterator.next();
+        PGPPublicKey subKey = keysIterator.next();
+        SecretKeyRingProtector protector = PasswordBasedSecretKeyRingProtector
+                .forKey(secretKeys, Passphrase.fromPassword("password123"));
+
+        SecretKeyRingEditorInterface editor = PGPainless.modifyKeyRing(secretKeys);
+        PGPSignature keyRevocation = editor.createRevocationCertificate(primaryKey.getKeyID(), protector, null);
+        PGPSignature subkeyRevocation = editor.createRevocationCertificate(subKey.getKeyID(), protector, null);
+
+        assertEquals(SignatureType.KEY_REVOCATION.getCode(), keyRevocation.getSignatureType());
+        assertEquals(SignatureType.SUBKEY_REVOCATION.getCode(), subkeyRevocation.getSignatureType());
+    }
 }