diff --git a/build.gradle.kts b/build.gradle.kts
index 04c1269..5b21e08 100644
--- a/build.gradle.kts
+++ b/build.gradle.kts
@@ -8,7 +8,7 @@ plugins {
 }
 
 group = "net.sergeych"
-version = "0.6.1-SNAPSHOT"
+version = "0.6.2-SNAPSHOT"
 
 repositories {
     mavenCentral()
diff --git a/src/commonMain/kotlin/net/sergeych/crypto2/ByteChunk.kt b/src/commonMain/kotlin/net/sergeych/crypto2/ByteChunk.kt
index 8885fe0..ff099e2 100644
--- a/src/commonMain/kotlin/net/sergeych/crypto2/ByteChunk.kt
+++ b/src/commonMain/kotlin/net/sergeych/crypto2/ByteChunk.kt
@@ -60,6 +60,8 @@ class ByteChunk(val data: UByteArray): Comparable<ByteChunk> {
      */
     val hex by lazy { data.encodeToHex() }
 
+    val base64Url by lazy { data.encodeToBase64Url() }
+
     /**
      * human-readable dump
      */
@@ -75,9 +77,14 @@ class ByteChunk(val data: UByteArray): Comparable<ByteChunk> {
 
     companion object {
         fun fromHex(hex: String): ByteChunk = ByteChunk(hex.decodeHex().asUByteArray())
+        fun random(sizeInBytes: Int=16) = randomUBytes(sizeInBytes).toChunk()
     }
 }
 
+private fun UByteArray.toChunk(): ByteChunk = ByteChunk(this)
+@Suppress("unused")
+private fun ByteArray.toChunk(): ByteChunk = ByteChunk(this.asUByteArray())
+
 @Suppress("unused")
 fun ByteArray.asChunk() = ByteChunk(toUByteArray())
 fun UByteArray.asChunk(): ByteChunk = ByteChunk(this)
\ No newline at end of file
diff --git a/src/commonMain/kotlin/net/sergeych/crypto2/Container.kt b/src/commonMain/kotlin/net/sergeych/crypto2/Container.kt
index 0a3e59f..7ae260c 100644
--- a/src/commonMain/kotlin/net/sergeych/crypto2/Container.kt
+++ b/src/commonMain/kotlin/net/sergeych/crypto2/Container.kt
@@ -155,6 +155,11 @@ sealed class Container {
     var authorisedByKey: PublicKey? = null
         protected set
 
+    /**
+     * List of [KeyId] of the keys that unlocked the container, in the same order used for encryption..
+     */
+    abstract val keyIds: List<KeyId>
+
 
     /**
      * @suppress
@@ -175,6 +180,8 @@ sealed class Container {
         override val decryptedWithKeyId: KeyId?
             get() = decryptedWithKey?.id
 
+        override val keyIds: List<KeyId> = listOf(keyId)
+
         init {
             decryptedData = creationData
         }
@@ -270,6 +277,8 @@ sealed class Container {
         override var decryptedWithKeyId: KeyId? = null
             private set
 
+        override val keyIds: List<KeyId> = encryptedKeys.map { it.tag }
+
         override fun decryptWith(keyRing: UniversalRing): UByteArray? {
             decryptedData?.let { return it }
             for (key in keyRing.decryptingKeys) {
diff --git a/src/commonMain/kotlin/net/sergeych/crypto2/SymmetricKey.kt b/src/commonMain/kotlin/net/sergeych/crypto2/SymmetricKey.kt
index f8b06af..7d5fc89 100644
--- a/src/commonMain/kotlin/net/sergeych/crypto2/SymmetricKey.kt
+++ b/src/commonMain/kotlin/net/sergeych/crypto2/SymmetricKey.kt
@@ -46,7 +46,7 @@ class SymmetricKey(
     override val nonceBytesLength: Int = nonceLength
 
     override val id by lazy {
-        KeyId(KeysmagicNumber.defaultSymmetric,blake2b3l(keyBytes), pbkdfParams)
+        KeyId(KeysmagicNumber.defaultSymmetric,blake2b3l(keyBytes),pbkdfParams)
     }
 
     override fun decryptWithNonce(cipherData: UByteArray, nonce: UByteArray): UByteArray =
diff --git a/src/commonMain/kotlin/net/sergeych/crypto2/kdf.kt b/src/commonMain/kotlin/net/sergeych/crypto2/kdf.kt
index 7deadf4..95fae61 100644
--- a/src/commonMain/kotlin/net/sergeych/crypto2/kdf.kt
+++ b/src/commonMain/kotlin/net/sergeych/crypto2/kdf.kt
@@ -27,10 +27,40 @@ sealed class KDF {
         Moderate,
         FixedHigher,
         Sensitive,
+        ;
+
+        /**
+         * Create [KDF] of the corresponding strength suitable to derive [numberOfKeys] symmetric keys.
+         *
+         * Random salt of proper size is used
+         */
+        fun kdfForSize(numberOfKeys: Int): KDF = creteDefault(SymmetricKey.keyLength*numberOfKeys, this)
+
+        /**
+         * Derive multiple keys from the password. Derivation params will be included in the key ids, see
+         * [SymmetricKey.id] as [KeyId.kdp].
+
+         * Random salt of proper size is used
+         *
+         * ___Important: symmetric keys do not save key ids___. _Container do it, so it is possible to re-derive
+         * key to open the container, but in many cases you might need to save [KeyId.kdp] separately_.
+         * Having no [PBKD.Params] it would not be possible to recreate the key, as complexity defaults tend
+         * to change with time.
+         */
+        @Suppress("unused")
+        fun deriveMultiple(password: String, count: Int): List<SymmetricKey> =
+            kdfForSize(count).deriveMultiple(password, count)
     }
 
+    /**
+     * Derive a single key from the password, same as [deriveMultiple] with `count==1`
+     */
     abstract fun derive(password: String): UByteArray
 
+    /**
+     * Derive keys from lower part of bytes derived from the password. E.g., if generated size is longer than
+     * required to create [count] keys, the first bytes will be used. It let use rest bytes for other purposes.
+     */
     fun deriveMultiple(password: String, count: Int): List<SymmetricKey> {
         val bytes = derive(password)
         val ks = SymmetricKey.keyLength
@@ -142,14 +172,14 @@ sealed class KDF {
                         salt, keySize
                     )
 
-                    Complexity.Sensitive -> Argon(
+                    Sensitive -> Argon(
                         Alg.default,
                         crypto_pwhash_OPSLIMIT_SENSITIVE,
                         crypto_pwhash_MEMLIMIT_SENSITIVE,
                         salt, keySize
                     )
 
-                    Complexity.FixedHigher -> Argon(
+                    FixedHigher -> Argon(
                         V2id_13,
                         4UL,
                         1073741824,
diff --git a/src/commonTest/kotlin/KDFTest.kt b/src/commonTest/kotlin/KDFTest.kt
index 84b7189..371fd18 100644
--- a/src/commonTest/kotlin/KDFTest.kt
+++ b/src/commonTest/kotlin/KDFTest.kt
@@ -38,4 +38,11 @@ class KDFTest {
         assertEquals(set2, set1)
     }
 
+    @Test
+    fun complexityTest() = runTest{
+        initCrypto()
+        val kk = KDF.Complexity.Interactive.kdfForSize(3).deriveMultiple("lala", 3)
+        assertEquals(3, kk.size)
+    }
+
 }
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