diff --git a/README.md b/README.md
index 6451fc3..dbe69e1 100644
--- a/README.md
+++ b/README.md
@@ -19,7 +19,7 @@ repositories {
   maven("https://gitea.sergeych.net/api/packages/SergeychWorks/maven")
 }
 dependencies {
-  import("net.sergeych:crypto2:0.5.6")  
+  import("net.sergeych:crypto2:0.5.7")  
 }
 ```
 
diff --git a/build.gradle.kts b/build.gradle.kts
index 0497bb8..3a9be63 100644
--- a/build.gradle.kts
+++ b/build.gradle.kts
@@ -8,7 +8,7 @@ plugins {
 }
 
 group = "net.sergeych"
-version = "0.5.6"
+version = "0.5.7"
 
 repositories {
     mavenCentral()
diff --git a/src/commonMain/kotlin/net/sergeych/crypto2/kdf.kt b/src/commonMain/kotlin/net/sergeych/crypto2/kdf.kt
index 46c6ef1..7deadf4 100644
--- a/src/commonMain/kotlin/net/sergeych/crypto2/kdf.kt
+++ b/src/commonMain/kotlin/net/sergeych/crypto2/kdf.kt
@@ -4,25 +4,39 @@ import com.ionspin.kotlin.crypto.pwhash.*
 import kotlinx.serialization.SerialName
 import kotlinx.serialization.Serializable
 import net.sergeych.bipack.Unsigned
+import net.sergeych.crypto2.KDF.Argon.Alg.V2id_13
+import net.sergeych.crypto2.KDF.Complexity.*
 import net.sergeych.crypto2.PBKD.Params
 
 @Serializable
 sealed class KDF {
 
+    /**
+     * KDF complexity: how many resources (CPY and RAM) it requires to transform a string to a key.
+     *
+     * Constants started with `Fixed...`, e.g., [FixedLow], [FixedMedium] and [FixedHigher]
+     * are first clas constants not to be changed in future but can become obsolete (too simple) with the
+     * development of the computer hardware. Other constants can change in future releases, so it is critical
+     * to serialize [KDF] or [PBKD.Params] generated with such constants and restore them before
+     * deriving keys.
+     */
     enum class Complexity {
+        FixedLow,
         Interactive,
+        FixedMedium,
         Moderate,
+        FixedHigher,
         Sensitive,
     }
 
     abstract fun derive(password: String): UByteArray
 
-    fun deriveMultiple(password: String,count: Int) : List<SymmetricKey> {
+    fun deriveMultiple(password: String, count: Int): List<SymmetricKey> {
         val bytes = derive(password)
         val ks = SymmetricKey.keyLength
-        check( ks * count <= bytes.size ) { "KDF is too short for $count keys: ${bytes.size} we need ${ks*count}"}
-        return (0 ..< count).map {
-            val base = it*ks
+        check(ks * count <= bytes.size) { "KDF is too short for $count keys: ${bytes.size} we need ${ks * count}" }
+        return (0..<count).map {
+            val base = it * ks
             Params(this, base, ks).deriveKey(password)
         }
     }
@@ -57,6 +71,7 @@ sealed class KDF {
         }
 
         enum class Alg(val code: Int) {
+            @Suppress("EnumEntryName", "unused")
             V2i_13(crypto_pwhash_argon2i_ALG_ARGON2I13),
             V2id_13(crypto_pwhash_argon2id_ALG_ARGON2ID13),
             ;
@@ -100,14 +115,27 @@ sealed class KDF {
                 require(salt.size == saltSize) { "The salt size should be $saltSize" }
                 require(keySize > minKeySize) { "The key size should be at least $keySize bytes" }
                 return when (complexity) {
-                    Complexity.Interactive -> Argon(
+                    FixedLow -> Argon(
+                        V2id_13,
+                        2UL,
+                        67108864,
+                        salt, keySize
+                    )
+
+                    Interactive -> Argon(
                         Alg.default,
                         crypto_pwhash_OPSLIMIT_INTERACTIVE.toULong(),
                         crypto_pwhash_MEMLIMIT_INTERACTIVE,
                         salt, keySize
                     )
 
-                    Complexity.Moderate -> Argon(
+                    FixedMedium -> Argon(
+                        V2id_13,
+                        3UL,
+                        268435456,
+                        salt, keySize
+                    )
+                    Moderate -> Argon(
                         Alg.default,
                         crypto_pwhash_OPSLIMIT_MODERATE,
                         crypto_pwhash_MEMLIMIT_MODERATE,
@@ -120,6 +148,14 @@ sealed class KDF {
                         crypto_pwhash_MEMLIMIT_SENSITIVE,
                         salt, keySize
                     )
+
+                    Complexity.FixedHigher -> Argon(
+                        V2id_13,
+                        4UL,
+                        1073741824,
+                        salt, keySize
+                    )
+
                 }
             }
         }
@@ -128,11 +164,11 @@ sealed class KDF {
     companion object {
         @Suppress("unused")
         fun creteDefault(keySize: Int, complexity: Complexity, salt: UByteArray = Argon.randomSalt()): KDF {
-            return Argon.create(complexity,salt,keySize)
+            return Argon.create(complexity, salt, keySize)
         }
     }
 
-    data class Instance(val kdf: KDF,val password: String)
+    data class Instance(val kdf: KDF, val password: String)
 
 }