+EncryptedKVStorage

src/commonMain/kotlin/net/sergeych/crypto2/EncryptedKVStorage.kt

@@ -0,0 +1,86 @@
+package net.sergeych.crypto2
+
+import net.sergeych.bintools.KVStorage
+import net.sergeych.bintools.MemoryKVStorage
+import net.sergeych.bintools.optStored
+import net.sergeych.synctools.ProtectedOp
+import net.sergeych.synctools.invoke
+import kotlin.random.Random
+import kotlin.random.nextUBytes
+
+/**
+ * Encrypted variant of [KVStorage]; the storage is encrypted with the given key
+ * in a given [plainStore] [KVStorage]. It is threadsafe where
+ * applicable. Also, it supports in-place key change [reEncrypt].
+ *
+ * Keys are stored encrypted and used hashed so it is not possible to
+ * retrieve them without knowing the encryption key.
+ */
+class EncryptedKVStorage(
+    private val plainStore: KVStorage,
+    private var encryptionKey: SymmetricKey,
+    private val prefix: String = "EKVS_"
+) : KVStorage {
+    private val op = ProtectedOp()
+
+    private val prefix2 = prefix + ":"
+
+    val seed: UByteArray
+
+    init {
+        var encryptedSeed by plainStore.optStored<UByteArray>("$prefix#seed")
+        seed = encryptedSeed?.let { encryptionKey.decrypt(it) }
+            ?: Random.nextUBytes(32).also {
+                encryptedSeed = encryptionKey.encrypt(it)
+            }
+    }
+
+    private fun mkkey(key: String): String =
+        blake2b(key.encodeToByteArray().asUByteArray() + seed).encodeToBase64Url()
+
+    override val keys: Set<String>
+        get() = op.invoke {
+            plainStore.keys.mapNotNull {
+                if (it.startsWith(prefix2))
+                    plainStore[it]?.let { encrypted ->
+                        encryptionKey.decrypt(encrypted.asUByteArray()).asByteArray().decodeToString()
+                    }
+                else null
+            }.toSet()
+        }
+
+    override fun get(key: String): ByteArray? = op {
+        val k0 = mkkey(key)
+        val k = prefix + k0
+        plainStore[k]?.let { encryptionKey.decrypt(it.asUByteArray()).asByteArray() }
+            ?.also {
+                val k2 = prefix2 + k0
+                if (k2 !in plainStore)
+                    plainStore[k2] = encryptionKey.encrypt(key).asByteArray()
+            }
+    }
+
+    override fun set(key: String, value: ByteArray?) {
+        op {
+            val k1 = mkkey(key)
+            plainStore[prefix + k1] = value?.let {
+                encryptionKey.encrypt(it.asUByteArray()).asByteArray()
+            }
+            plainStore[prefix2 + k1] = encryptionKey.encrypt(key).asByteArray()
+        }
+    }
+
+    /**
+     * Re-encrypts the entire storage in-place with the given key; it is threadsafe where
+     * applicable.
+     *
+     * This method re-encrypts every data item so it is cryptographically secure.
+     */
+    fun reEncrypt(newKey: SymmetricKey) {
+        op {
+            val copy = MemoryKVStorage().also { it.addAll(this) }
+            encryptionKey = newKey
+            addAll(copy)
+        }
+    }
+}