1 files changed, 43 insertions, 0 deletions
diff --git a/src/util.ts b/src/util.ts
new file mode 100644
index 0000000..b5cbd4b
--- /dev/null
+++ b/src/util.ts
@@ -0,0 +1,43 @@
+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(data)
+      .update(',')
+      .update(key)
+      .digest('hex')
+  }
+}