finalize multi-device

WASignalGroup/sender_chain_key.js

@@ -0,0 +1,50 @@
+const SenderMessageKey = require('./sender_message_key');
+//const HKDF = require('./hkdf');
+const crypto = require('libsignal/src/crypto');
+
+class SenderChainKey {
+  MESSAGE_KEY_SEED = Buffer.from([0x01]);
+
+  CHAIN_KEY_SEED = Buffer.from([0x02]);
+
+  iteration = 0;
+
+  chainKey = Buffer.alloc(0);
+
+  constructor(iteration, chainKey) {
+    this.iteration = iteration;
+    this.chainKey = chainKey;
+  }
+
+  getIteration() {
+    return this.iteration;
+  }
+
+  getSenderMessageKey() {
+    return new SenderMessageKey(
+      this.iteration,
+      this.getDerivative(this.MESSAGE_KEY_SEED, this.chainKey)
+    );
+  }
+
+  getNext() {
+    return new SenderChainKey(
+      this.iteration + 1,
+      this.getDerivative(this.CHAIN_KEY_SEED, this.chainKey)
+    );
+  }
+
+  getSeed() {
+    return typeof this.chainKey === 'string' ? Buffer.from(this.chainKey, 'base64') : this.chainKey;
+  }
+
+  getDerivative(seed, key) {
+    key = typeof key === 'string' ? Buffer.from(key, 'base64') : key;
+    const hash = crypto.calculateMAC(key, seed);
+    //const hash = new Hash().hmac_hash(key, seed, 'sha256', '');
+    
+    return hash;
+  }
+}
+
+module.exports = SenderChainKey;