Generalizes fixed key setup

quartz/src/androidMain/kotlin/com/vitorpamplona/quartz/nip44Encryption/crypto/FixedKey.kt

@@ -0,0 +1,46 @@
+/**
+ * Copyright (c) 2025 Vitor Pamplona
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to use,
+ * copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the
+ * Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
+ * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+package com.vitorpamplona.quartz.nip44Encryption.crypto
+
+import javax.crypto.SecretKey
+
+class FixedKey(
+    val key: ByteArray,
+    val algo: String,
+) : SecretKey {
+    override fun getAlgorithm() = algo
+
+    override fun getEncoded() = key
+
+    override fun getFormat() = "RAW"
+
+    override fun hashCode() = key.contentHashCode()
+
+    override fun equals(other: Any?): Boolean {
+        if (this === other) return true
+        if (other !is FixedKey) return false
+        return key.contentEquals(other.key)
+    }
+
+    override fun destroy() = key.fill(0)
+
+    override fun isDestroyed() = key.all { it.toInt() == 0 }
+}

quartz/src/androidMain/kotlin/com/vitorpamplona/quartz/nip44Encryption/crypto/Hkdf.kt

@@ -23,7 +23,6 @@ package com.vitorpamplona.quartz.nip44Encryption.crypto
 import com.vitorpamplona.quartz.nip44Encryption.Nip44v2.MessageKey
 import java.nio.ByteBuffer
 import javax.crypto.Mac
-import javax.crypto.SecretKey
 import javax.crypto.spec.SecretKeySpec
 
 class Hkdf(
@@ -35,7 +34,7 @@ class Hkdf(
         salt: ByteArray,
     ): ByteArray {
         val mac = Mac.getInstance(algorithm)
-        mac.init(HMacKey(salt))
+        mac.init(FixedKey(salt, algorithm))
         return mac.doFinal(key)
     }
 
@@ -45,7 +44,7 @@ class Hkdf(
         salt: ByteArray,
     ): ByteArray {
         val mac = Mac.getInstance(algorithm)
-        mac.init(HMacKey(salt))
+        mac.init(FixedKey(salt, algorithm))
         mac.update(key1)
         mac.update(key2)
         return mac.doFinal()
@@ -95,7 +94,7 @@ class Hkdf(
         check(nonce.size == hashLen)
 
         val mac = Mac.getInstance(algorithm)
-        mac.init(HMacKey(key))
+        mac.init(FixedKey(key, algorithm))
 
         // First round: T(1) = HMAC-SHA256(key, nonce || 0x01)
         mac.update(nonce)
@@ -125,25 +124,3 @@ class Hkdf(
         )
     }
 }
-
-class HMacKey(
-    val key: ByteArray,
-) : SecretKey {
-    override fun getAlgorithm() = "HmacSHA256"
-
-    override fun getEncoded() = key
-
-    override fun getFormat() = "RAW"
-
-    override fun hashCode() = key.contentHashCode()
-
-    override fun equals(other: Any?): Boolean {
-        if (this === other) return true
-        if (other !is HMacKey) return false
-        return key.contentEquals(other.key)
-    }
-
-    override fun destroy() = key.fill(0)
-
-    override fun isDestroyed() = key.all { it.toInt() == 0 }
-}