Add method to change expiration time of subkeys

Port of e06f60f62c to kotlin

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

@@ -8,6 +8,7 @@ import java.util.*
 import java.util.function.Predicate
 import javax.annotation.Nonnull
 import kotlin.NoSuchElementException
+import openpgp.openPgpKeyId
 import org.bouncycastle.bcpg.sig.KeyExpirationTime
 import org.bouncycastle.extensions.getKeyExpirationDate
 import org.bouncycastle.extensions.publicKeyAlgorithm
@@ -460,6 +461,28 @@ class SecretKeyRingEditor(
         return this
     }
 
+    override fun setExpirationDateOfSubkey(
+        expiration: Date?,
+        keyId: Long,
+        protector: SecretKeyRingProtector
+    ): SecretKeyRingEditorInterface = apply {
+        // is primary key
+        if (keyId == secretKeyRing.publicKey.keyID) {
+            return setExpirationDate(expiration, protector)
+        }
+
+        // is subkey
+        val subkey =
+            secretKeyRing.getPublicKey(keyId)
+                ?: throw NoSuchElementException("No subkey with ID ${keyId.openPgpKeyId()} found.")
+        val prevBinding =
+            inspectKeyRing(secretKeyRing).getCurrentSubkeyBindingSignature(keyId)
+                ?: throw NoSuchElementException(
+                    "Previous subkey binding signaure for ${keyId.openPgpKeyId()} MUST NOT be null.")
+        val bindingSig = reissueSubkeyBindingSignature(subkey, expiration, protector, prevBinding)
+        secretKeyRing = injectCertification(secretKeyRing, subkey, bindingSig)
+    }
+
     override fun createMinimalRevocationCertificate(
         protector: SecretKeyRingProtector,
         revocationAttributes: RevocationAttributes?
@@ -676,6 +699,45 @@ class SecretKeyRingEditor(
             .build()
     }
 
+    private fun reissueSubkeyBindingSignature(
+        subkey: PGPPublicKey,
+        expiration: Date?,
+        protector: SecretKeyRingProtector,
+        prevSubkeyBindingSignature: PGPSignature
+    ): PGPSignature {
+        val primaryKey = secretKeyRing.publicKey
+        val secretPrimaryKey = secretKeyRing.secretKey
+        val secretSubkey: PGPSecretKey? = secretKeyRing.getSecretKey(subkey.keyID)
+
+        val builder =
+            SubkeyBindingSignatureBuilder(secretPrimaryKey, protector, prevSubkeyBindingSignature)
+        builder.hashedSubpackets.apply {
+            // set expiration
+            setSignatureCreationTime(referenceTime)
+            setKeyExpirationTime(subkey, expiration)
+            setSignatureExpirationTime(null) // avoid copying sig exp time
+
+            // signing-capable subkeys need embedded primary key binding sig
+            SignatureSubpacketsUtil.parseKeyFlags(prevSubkeyBindingSignature)?.let { flags ->
+                if (flags.contains(KeyFlag.SIGN_DATA)) {
+                    if (secretSubkey == null) {
+                        throw NoSuchElementException(
+                            "Secret key does not contain secret-key" +
+                                " component for subkey ${subkey.keyID.openPgpKeyId()}")
+                    }
+
+                    // create new embedded back-sig
+                    clearEmbeddedSignatures()
+                    addEmbeddedSignature(
+                        PrimaryKeyBindingSignatureBuilder(secretSubkey, protector)
+                            .build(primaryKey))
+                }
+            }
+        }
+
+        return builder.build(subkey)
+    }
+
     private fun selectUserIds(predicate: Predicate<String>): List<String> =
         inspectKeyRing(secretKeyRing).validUserIds.filter { predicate.test(it) }
 

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

@@ -469,6 +469,24 @@ interface SecretKeyRingEditorInterface {
         protector: SecretKeyRingProtector
     ): SecretKeyRingEditorInterface
 
+    /**
+     * Set the expiration date for the subkey identified by the given keyId to the given expiration
+     * date. If the key is supposed to never expire, then an expiration date of null is expected.
+     *
+     * @param expiration new expiration date of null
+     * @param keyId id of the subkey
+     * @param protector to unlock the secret key
+     * @return the builder
+     * @throws PGPException in case we cannot generate a new subkey-binding or self-signature with
+     *   the changed expiration date
+     */
+    @Throws(PGPException::class)
+    fun setExpirationDateOfSubkey(
+        expiration: Date?,
+        keyId: Long,
+        protector: SecretKeyRingProtector
+    ): SecretKeyRingEditorInterface
+
     /**
      * Create a minimal, self-authorizing revocation certificate, containing only the primary key
      * and a revocation signature. This type of revocation certificates was introduced in OpenPGP

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

@@ -0,0 +1,90 @@
+// SPDX-FileCopyrightText: 2023 Paul Schaub <vanitasvitae@fsfe.org>
+//
+// SPDX-License-Identifier: Apache-2.0
+
+package org.pgpainless.key.modification;
+
+import org.bouncycastle.openpgp.PGPPublicKey;
+import org.bouncycastle.openpgp.PGPSecretKeyRing;
+import org.junit.JUtils;
+import org.junit.jupiter.api.Test;
+import org.pgpainless.PGPainless;
+import org.pgpainless.algorithm.EncryptionPurpose;
+import org.pgpainless.key.OpenPgpFingerprint;
+import org.pgpainless.key.OpenPgpV4Fingerprint;
+import org.pgpainless.key.protection.SecretKeyRingProtector;
+import org.pgpainless.util.DateUtil;
+
+import java.io.IOException;
+import java.util.Date;
+
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertNull;
+
+public class ChangeSubkeyExpirationTimeTest {
+
+    @Test
+    public void changeExpirationTimeOfSubkey() {
+        PGPSecretKeyRing secretKeys = PGPainless.generateKeyRing().modernKeyRing("Alice");
+        Date now = secretKeys.getPublicKey().getCreationTime();
+        Date inAnHour = new Date(now.getTime() + 1000 * 60 * 60);
+        PGPPublicKey encryptionKey = PGPainless.inspectKeyRing(secretKeys)
+                .getEncryptionSubkeys(EncryptionPurpose.ANY).get(0);
+        secretKeys = PGPainless.modifyKeyRing(secretKeys)
+                .setExpirationDateOfSubkey(
+                        inAnHour,
+                        encryptionKey.getKeyID(),
+                        SecretKeyRingProtector.unprotectedKeys())
+                .done();
+
+        JUtils.assertDateEquals(inAnHour, PGPainless.inspectKeyRing(secretKeys)
+                .getSubkeyExpirationDate(OpenPgpFingerprint.of(encryptionKey)));
+    }
+
+    @Test
+    public void changeExpirationTimeOfExpiredSubkey() throws IOException {
+        PGPSecretKeyRing secretKeys = PGPainless.readKeyRing().secretKeyRing(
+                "-----BEGIN PGP PRIVATE KEY BLOCK-----\n" +
+                        "Version: PGPainless\n" +
+                        "Comment: CA52 4D5D E3D8 9CD9 105B  BA45 3761 076B C6B5 3000\n" +
+                        "Comment: Alice <alice@pgpainless.org>\n" +
+                        "\n" +
+                        "lFgEZXHykRYJKwYBBAHaRw8BAQdATArrVxPEpuA/wcayAxRl/v1tIYJSe4MCA/fO\n" +
+                        "84CFgpcAAP9uZkLjoBIQAjUTEiS8Wk3sui3u4mJ4WVQEpNhQSpq37g8gtBxBbGlj\n" +
+                        "ZSA8YWxpY2VAcGdwYWlubGVzcy5vcmc+iJUEExYKAEcFAmVx8pIJEDdhB2vGtTAA\n" +
+                        "FiEEylJNXePYnNkQW7pFN2EHa8a1MAACngECmwEFFgIDAQAECwkIBwUVCgkICwWJ\n" +
+                        "CWYBgAKZAQAAG3oA/0iJbwyjGOTa2RlgBKdmFjlBG5uwMGheKge/aZBbdUd8AQCB\n" +
+                        "8NFWmyLlne4hDMM2g8RFf/W156wnyTH7jTQLx2sZDJxYBGVx8pIWCSsGAQQB2kcP\n" +
+                        "AQEHQLQt6ns7yTxLvIWXqFCekh6QEvUumhHvCTjZPXa/UxCNAAEA+FHhZ1uik6PN\n" +
+                        "Pwli9Tp9QGddf3pwQw+OL/K7gpZO3sgQHYjVBBgWCgB9BQJlcfKSAp4BApsCBRYC\n" +
+                        "AwEABAsJCAcFFQoJCAtfIAQZFgoABgUCZXHykgAKCRCRKlHdDPaYKjyZAQD10Km4\n" +
+                        "Qs37yF9bntS+z9Va7AMUuBlzYF5H/nXCRuqQTAEA60q++7Xwj94yLfoAfxH0V6Wd\n" +
+                        "L2rDJCDZ3FFMlycToQMACgkQN2EHa8a1MADmDgD9EGzH6pPYRW5vWQGXNsr7PMWK\n" +
+                        "LlBnevc0DaVWEHTu9tcA/iezQ9R+A90qcE1+HeNIJbSB89yIoJje2vePRV/JakAI\n" +
+                        "nF0EZXHykhIKKwYBBAGXVQEFAQEHQOiLc02OQJD9qdpsyR6bJ52Cu8rUMlEJOELz\n" +
+                        "1858OoQyAwEIBwAA/3YkHGmnVaQvUpSwlCInOvHvjLNLH9b9Lh/OxiuSoMgIEASI\n" +
+                        "dQQYFgoAHQUCZXHykgKeAQKbDAUWAgMBAAQLCQgHBRUKCQgLAAoJEDdhB2vGtTAA\n" +
+                        "1nkBAPAUcHxI1O+fE/QzuLANLHDeWc3Mc09KKnWoTkt/kk5VAQCIPlKQAcmmKdYE\n" +
+                        "Tiz8woSKLQKswKr/jVMqnUiGPsU/DoiSBBgWCgBECRA3YQdrxrUwABYhBMpSTV3j\n" +
+                        "2JzZEFu6RTdhB2vGtTAABYJlcfL6Ap4BApsMBRYCAwEABAsJCAcFFQoJCAsFiQAA\n" +
+                        "AGgAAMNmAQDN/TML2zdgBNkfh7TIqbI4Flx54Yi7qEjSXg0Z+tszHgD/e1Bf+xEs\n" +
+                        "BC9ewVsyQsnj3B0FliGYaPiQeoY/FGBmYQs=\n" +
+                        "=5Ur6\n" +
+                        "-----END PGP PRIVATE KEY BLOCK-----"
+        );
+        assertNotNull(secretKeys);
+
+        // subkey is expired at 2023-12-07 16:29:46 UTC
+        OpenPgpFingerprint encryptionSubkey = new OpenPgpV4Fingerprint("2E541354A23C9943375EC27A3EF133ED8720D636");
+        JUtils.assertDateEquals(
+                DateUtil.parseUTCDate("2023-12-07 16:29:46 UTC"),
+                PGPainless.inspectKeyRing(secretKeys).getSubkeyExpirationDate(encryptionSubkey));
+
+        // re-validate the subkey by setting its expiry to null (no expiry)
+        secretKeys = PGPainless.modifyKeyRing(secretKeys)
+                .setExpirationDateOfSubkey(null, encryptionSubkey.getKeyId(), SecretKeyRingProtector.unprotectedKeys())
+                .done();
+
+        assertNull(PGPainless.inspectKeyRing(secretKeys).getSubkeyExpirationDate(encryptionSubkey));
+    }
+}