diff --git a/docs/cryptography/signing.md b/docs/cryptography/signing.md
index f0d3aa6..b6534d8 100644
--- a/docs/cryptography/signing.md
+++ b/docs/cryptography/signing.md
@@ -54,6 +54,19 @@ Where `/users/uuid/inbox` is the path of the request.
 Here is an example of signing a request using TypeScript and the WebCrypto API:
 
 ```typescript
+/**
+ * Convert a string into an ArrayBuffer
+ * from https://developers.google.com/web/updates/2012/06/How-to-convert-ArrayBuffer-to-and-from-String
+ */
+const str2ab = (str: string) => {
+	const buf = new ArrayBuffer(str.length);
+	const bufView = new Uint8Array(buf);
+	for (let i = 0, strLen = str.length; i < strLen; i++) {
+		bufView[i] = str.charCodeAt(i);
+	}
+	return buf;
+};
+
 const privateKey = await crypto.subtle.importKey(
     "pkcs8",
     str2ab(atob("base64_private_key")),