Use fnv1a instead of SHA256 to create images signatures (#2353)

Author: jpreynat

bun.lockb

@@ -24,6 +24,7 @@
         "@radix-ui/react-checkbox": "^1.0.4",
         "@radix-ui/react-popover": "^1.0.7",
         "@sentry/nextjs": "^7.94.1",
+        "@sindresorhus/fnv1a": "^3.1.0",
         "@tailwindcss/container-queries": "^0.1.1",
         "@tailwindcss/typography": "^0.5.10",
         "@upstash/redis": "^1.27.1",

package.json

@@ -13,6 +13,9 @@ export const runtime = 'edge';
 export async function GET(request: NextRequest) {
     let urlParam = request.nextUrl.searchParams.get('url');
     const signature = request.nextUrl.searchParams.get('sign');
+    // The current signature algorithm sets version as 1, but we need to support the older version as well
+    // for previously generated content. In this case, we default to version 0.
+    const signatureVersion = (request.nextUrl.searchParams.get('sv') as '1') || '0';
     if (!urlParam || !signature) {
         return new Response('Missing url/sign parameters', { status: 400 });
     }
@@ -25,7 +28,7 @@ export async function GET(request: NextRequest) {
     }
 
     // Verify the signature
-    const verified = await verifyImageSignature(url, signature);
+    const verified = await verifyImageSignature(url, { signature, version: signatureVersion });
     if (!verified) {
         return new Response(`Invalid signature "${signature ?? ''}" for "${url}"`, { status: 400 });
     }

src/app/(global)/~gitbook/image/route.ts

@@ -1,5 +1,7 @@
 import 'server-only';
 
+import fnv1a from '@sindresorhus/fnv1a';
+
 import { noCacheFetchOptions } from '@/lib/cache/http';
 
 import { rootUrl } from './links';
@@ -73,7 +75,7 @@ export async function getResizedImageURL(
         return null;
     }
 
-    const signature = await generateSignature(input);
+    const signature = await generateSignatureV1(input);
 
     return (options) => {
         const url = new URL('/~gitbook/image', rootUrl());
@@ -93,6 +95,7 @@ export async function getResizedImageURL(
         }
 
         url.searchParams.set('sign', signature);
+        url.searchParams.set('sv', '1');
 
         return url.toString();
     };
@@ -101,8 +104,12 @@ export async function getResizedImageURL(
 /**
  * Verify a signature of an image URL
  */
-export async function verifyImageSignature(input: string, signature: string): Promise<boolean> {
-    const expectedSignature = await generateSignature(input);
+export async function verifyImageSignature(
+    input: string,
+    { signature, version }: { signature: string; version: '1' | '0' },
+): Promise<boolean> {
+    const expectedSignature =
+        version === '1' ? await generateSignatureV1(input) : await generateSignatureV0(input);
     return expectedSignature === signature;
 }
 
@@ -201,7 +208,25 @@ function stringifyOptions(options: CloudflareImageOptions): string {
     }, '');
 }
 
-async function generateSignature(input: string): Promise<string> {
+// Reused buffer for FNV-1a hashing
+const fnv1aUtf8Buffer = new Uint8Array(512);
+
+/**
+ * New and faster algorithm to generate a signature for an image.
+ * When setting it in a URL, we use version '1' for the 'sv' querystring parameneter
+ * to know that it was the algorithm that was used.
+ */
+async function generateSignatureV1(input: string): Promise<string> {
+    const all = [input, process.env.GITBOOK_IMAGE_RESIZE_SIGNING_KEY].filter(Boolean).join(':');
+    return fnv1a(all, { utf8Buffer: fnv1aUtf8Buffer }).toString(16);
+}
+
+/**
+ * Initial algorithm used to generate a signature for an image. It didn't use any versioning in the URL.
+ * We still need it to validate older signatures that were generated without versioning
+ * but still exist in previously generated and cached content.
+ */
+async function generateSignatureV0(input: string): Promise<string> {
     const all = [input, process.env.GITBOOK_IMAGE_RESIZE_SIGNING_KEY].filter(Boolean).join(':');
     const hash = await crypto.subtle.digest('SHA-256', new TextEncoder().encode(all));