2 files changed, 32 insertions, 8 deletions
diff --git a/packages/airmx/src/airmx.ts b/packages/airmx/src/airmx.ts
index 1050bf0..a507260 100644
--- a/packages/airmx/src/airmx.ts
+++ b/packages/airmx/src/airmx.ts
@@ -1,4 +1,3 @@
-import crypto from 'crypto'
 import { MqttClient } from 'mqtt'
 
 import type {
@@ -138,12 +137,8 @@ export class Airmx {
 
   #validateMessage(deviceId: number, message: string, sig: string) {
     const device = this.#getDevice(deviceId)
-    const plainText = message.slice(1, message.lastIndexOf('"sig"'))
-    const calculated = crypto
-      .createHash('md5')
-      .update(plainText)
-      .update(device.key)
-      .digest('hex')
+    const plainText = message.slice(1, message.lastIndexOf(',"sig"'))
+    const calculated = this.#signer.signText(plainText, device.key)
     if (calculated !== sig) {
       throw new Error('Failed to validate the message.')
     }
diff --git a/packages/airmx/src/util.ts b/packages/airmx/src/util.ts
index 496ae56..b5cbd4b 100644
--- a/packages/airmx/src/util.ts
+++ b/packages/airmx/src/util.ts
@@ -2,11 +2,40 @@ import crypto from 'crypto'
 import type { CommandMessage } from './messages.js'
 
 export class Signer {
+  /**
+   * Calculate the signature for the message.
+   *
+   * @param message - The command message.
+   * @param key - The device key.
+   * @returns An 8-byte signature for the given message.
+   */
   sign(message: CommandMessage<unknown>, key: string) {
     const plainText = JSON.stringify(message.payload())
+    return this.#hash(plainText.slice(1, -1), key)
+  }
+
+  /**
+   * Calculate the signature for the plain text.
+   *
+   * @param message - The plain text.
+   * @param key - The device key.
+   * @returns An 8-byte signature for the given text.
+   */
+  signText(message: string, key: string) {
+    return this.#hash(message, key)
+  }
+
+  /**
+   * Hash the data with the MD5 algorithm.
+   *
+   * @param data - The plain text.
+   * @param key - The device key.
+   * @returns An 8-byte signature for the given data.
+   */
+  #hash(data: string, key: string) {
     return crypto
       .createHash('md5')
-      .update(plainText.slice(1, -1))
+      .update(data)
       .update(',')
       .update(key)
       .digest('hex')