Quick and dirty hardware key import

3 files changed, 116 insertions, 3 deletions

diff --git a/crypto-pgpainless/src/main/kotlin/app/passwordstore/crypto/KeyUtils.kt b/crypto-pgpainless/src/main/kotlin/app/passwordstore/crypto/KeyUtils.kt
index d1487903..bd303e66 100644
--- a/crypto-pgpainless/src/main/kotlin/app/passwordstore/crypto/KeyUtils.kt
+++ b/crypto-pgpainless/src/main/kotlin/app/passwordstore/crypto/KeyUtils.kt
@@ -9,7 +9,15 @@ import app.passwordstore.crypto.GpgIdentifier.KeyId
 import app.passwordstore.crypto.GpgIdentifier.UserId
 import com.github.michaelbull.result.get
 import com.github.michaelbull.result.runCatching
+import java.io.ByteArrayOutputStream
+import org.bouncycastle.bcpg.GnuExtendedS2K
+import org.bouncycastle.bcpg.S2K
+import org.bouncycastle.bcpg.SecretKeyPacket
+import org.bouncycastle.bcpg.SecretSubkeyPacket
+import org.bouncycastle.bcpg.SymmetricKeyAlgorithmTags
 import org.bouncycastle.openpgp.PGPKeyRing
+import org.bouncycastle.openpgp.PGPPublicKey
+import org.bouncycastle.openpgp.PGPPublicKeyRing
 import org.bouncycastle.openpgp.PGPSecretKey
 import org.bouncycastle.openpgp.PGPSecretKeyRing
 import org.pgpainless.algorithm.EncryptionPurpose
@@ -37,6 +45,29 @@ public object KeyUtils {
     val keyRing = tryParseKeyring(key) ?: return null
     return UserId(keyRing.publicKey.userIDs.next())
   }
+
+  public fun tryCreateStubKey(
+    publicKey: PGPKey,
+    serial: ByteArray,
+    stubFingerprints: List<OpenPgpFingerprint>
+  ): PGPKey? {
+    val keyRing = tryParseKeyring(publicKey) as? PGPPublicKeyRing ?: return null
+    val secretKeyRing =
+      keyRing
+        .fold(PGPSecretKeyRing(emptyList())) { ring, key ->
+          PGPSecretKeyRing.insertSecretKey(
+            ring,
+            if (stubFingerprints.any { it == OpenPgpFingerprint.parseFromBinary(key.fingerprint) }) {
+              toCardSecretKey(key, serial)
+            } else {
+              toDummySecretKey(key)
+            }
+          )
+        }
+
+    return PGPKey(secretKeyRing.encoded)
+  }
+
   public fun tryGetEncryptionKeyFingerprint(key: PGPKey): OpenPgpFingerprint? {
     val keyRing = tryParseKeyring(key) ?: return null
     val encryptionSubkey =
@@ -59,3 +90,63 @@ public object KeyUtils {
     return info.getSecretKey(encryptionKey.keyID)
   }
 }
+
+private fun toDummySecretKey(publicKey: PGPPublicKey): PGPSecretKey {
+
+  return PGPSecretKey(
+    if (publicKey.isMasterKey) {
+      SecretKeyPacket(
+        publicKey.publicKeyPacket,
+        SymmetricKeyAlgorithmTags.NULL,
+        SecretKeyPacket.USAGE_CHECKSUM,
+        GnuExtendedS2K(S2K.GNU_PROTECTION_MODE_NO_PRIVATE_KEY),
+        byteArrayOf(),
+        byteArrayOf()
+      )
+    } else {
+      SecretSubkeyPacket(
+        publicKey.publicKeyPacket,
+        SymmetricKeyAlgorithmTags.NULL,
+        SecretKeyPacket.USAGE_CHECKSUM,
+        GnuExtendedS2K(S2K.GNU_PROTECTION_MODE_NO_PRIVATE_KEY),
+        byteArrayOf(),
+        byteArrayOf()
+      )
+    },
+    publicKey
+  )
+}
+
+@Suppress("MagicNumber")
+private fun toCardSecretKey(publicKey: PGPPublicKey, serial: ByteArray): PGPSecretKey {
+  return PGPSecretKey(
+    if (publicKey.isMasterKey) {
+      SecretKeyPacket(
+        publicKey.publicKeyPacket,
+        SymmetricKeyAlgorithmTags.NULL,
+        SecretKeyPacket.USAGE_CHECKSUM,
+        GnuExtendedS2K(S2K.GNU_PROTECTION_MODE_DIVERT_TO_CARD),
+        ByteArray(8),
+        encodeSerial(serial),
+      )
+    } else {
+      SecretSubkeyPacket(
+        publicKey.publicKeyPacket,
+        SymmetricKeyAlgorithmTags.NULL,
+        SecretKeyPacket.USAGE_CHECKSUM,
+        GnuExtendedS2K(S2K.GNU_PROTECTION_MODE_DIVERT_TO_CARD),
+        ByteArray(8),
+        encodeSerial(serial),
+      )
+    },
+    publicKey
+  )
+}
+
+@Suppress("MagicNumber")
+private fun encodeSerial(serial: ByteArray): ByteArray {
+  val out = ByteArrayOutputStream()
+  out.write(serial.size)
+  out.write(serial, 0, minOf(16, serial.size))
+  return out.toByteArray()
+}
diff --git a/crypto-pgpainless/src/main/kotlin/app/passwordstore/crypto/PGPKeyManager.kt b/crypto-pgpainless/src/main/kotlin/app/passwordstore/crypto/PGPKeyManager.kt
index be2ec474..786694d4 100644
--- a/crypto-pgpainless/src/main/kotlin/app/passwordstore/crypto/PGPKeyManager.kt
+++ b/crypto-pgpainless/src/main/kotlin/app/passwordstore/crypto/PGPKeyManager.kt
@@ -9,12 +9,12 @@ package app.passwordstore.crypto
 import androidx.annotation.VisibleForTesting
 import app.passwordstore.crypto.KeyUtils.tryGetId
 import app.passwordstore.crypto.KeyUtils.tryParseKeyring
-import app.passwordstore.crypto.errors.InvalidKeyException
 import app.passwordstore.crypto.errors.KeyAlreadyExistsException
 import app.passwordstore.crypto.errors.KeyDeletionFailedException
 import app.passwordstore.crypto.errors.KeyDirectoryUnavailableException
 import app.passwordstore.crypto.errors.KeyNotFoundException
 import app.passwordstore.crypto.errors.NoKeysAvailableException
+import app.passwordstore.crypto.errors.NoSecretKeyException
 import app.passwordstore.util.coroutines.runSuspendCatching
 import com.github.michaelbull.result.Result
 import com.github.michaelbull.result.unwrap
@@ -40,12 +40,17 @@ constructor(
     withContext(dispatcher) {
       runSuspendCatching {
         if (!keyDirExists()) throw KeyDirectoryUnavailableException
-        val incomingKeyRing = tryParseKeyring(key) ?: throw InvalidKeyException
+        val incomingKeyRing = tryParseKeyring(key)
+
+        if (incomingKeyRing is PGPPublicKeyRing) {
+          throw NoSecretKeyException(tryGetId(key)?.toString() ?: "Failed to retrieve key ID")
+        }
+
         val keyFile = File(keyDir, "${tryGetId(key)}.$KEY_EXTENSION")
         if (keyFile.exists()) {
           val existingKeyBytes = keyFile.readBytes()
           val existingKeyRing =
-            tryParseKeyring(PGPKey(existingKeyBytes)) ?: throw InvalidKeyException
+            tryParseKeyring(PGPKey(existingKeyBytes))
           when {
             existingKeyRing is PGPPublicKeyRing && incomingKeyRing is PGPSecretKeyRing -> {
               keyFile.writeBytes(key.contents)
diff --git a/crypto-pgpainless/src/main/kotlin/org/bouncycastle/bcpg/GnuExtendedS2K.kt b/crypto-pgpainless/src/main/kotlin/org/bouncycastle/bcpg/GnuExtendedS2K.kt
new file mode 100644
index 00000000..a5ebad78
--- /dev/null
+++ b/crypto-pgpainless/src/main/kotlin/org/bouncycastle/bcpg/GnuExtendedS2K.kt
@@ -0,0 +1,17 @@
+package org.bouncycastle.bcpg
+
+/**
+ * Add a constructor for GNU-extended S2K
+ *
+ * This extension is documented on GnuPG documentation DETAILS file,
+ * section "GNU extensions to the S2K algorithm". Its support is
+ * already present in S2K class but lack for a constructor.
+ *
+ * @author Léonard Dallot <leonard.dallot@taztag.com>
+ */
+public class GnuExtendedS2K(mode: Int) : S2K(SIMPLE) {
+  init {
+    this.type = GNU_DUMMY_S2K
+    this.protectionMode = mode
+  }
+}