diff --git a/src/commonMain/kotlin/net.sergeych.superlogin/DerivedKeys.kt b/src/commonMain/kotlin/net.sergeych.superlogin/DerivedKeys.kt
index 368965e..6848ce0 100644
--- a/src/commonMain/kotlin/net.sergeych.superlogin/DerivedKeys.kt
+++ b/src/commonMain/kotlin/net.sergeych.superlogin/DerivedKeys.kt
@@ -3,13 +3,20 @@ package net.sergeych.superlogin
 import net.sergeych.unikrypto.SymmetricKey
 
 /**
- * Super creds are derived from a password and given derivatino parameters.
- * They should not being sent over the netowkr as is or stored so it is not serializable.
+ * Super creds are derived from a password and given derivation parameters.
+ * They should not be being sent over the network or stored (re-derivation is
+ * usually required), so it is not serializable.
+ * @param loginId cryptographically independent and strong id that depends on the password
+ *                but does not disclose [loginAccessKey], Superlogin uses it to allow
+ *                API access to ACO with login private key (it can be safely stored in the
+ *                database)
+ * @param loginAccessKey first symmetric key, used to decrypt ACO
+ * @param extraKey just for future extensions. not used as for now.
  */
 class DerivedKeys(
     val loginId: ByteArray,
     val loginAccessKey: SymmetricKey,
-    val systemAccessKey: SymmetricKey
+    @Suppress("unused") val extraKey: SymmetricKey
 ) {
 
    companion object {