diff --git a/web/src/lib/crypto.worker.ts b/web/src/lib/crypto.worker.ts
new file mode 100644
index 0000000..ee92105
--- /dev/null
+++ b/web/src/lib/crypto.worker.ts
@@ -0,0 +1,23 @@
+import { importKey, encrypt, decrypt } from "./crypto";
+
+self.onmessage = async (e: MessageEvent) => {
+  const { type, keyEncoded } = e.data;
+  try {
+    const key = await importKey(keyEncoded);
+
+    if (type === "encrypt") {
+      const { fileName, fileBuffer } = e.data;
+      const ciphertext = await encrypt(fileName, fileBuffer, key);
+      self.postMessage({ ciphertext }, [ciphertext.buffer]);
+    } else if (type === "decrypt") {
+      const { ciphertext } = e.data;
+      const { fileName, fileData } = await decrypt(
+        new Uint8Array(ciphertext),
+        key,
+      );
+      self.postMessage({ fileName, fileData }, [fileData.buffer]);
+    }
+  } catch (err: any) {
+    self.postMessage({ error: err.message });
+  }
+};
diff --git a/web/src/pages/Upload.tsx b/web/src/pages/Upload.tsx
index 1beb52e..84531b9 100644
--- a/web/src/pages/Upload.tsx
+++ b/web/src/pages/Upload.tsx
@@ -7,7 +7,7 @@ import {
   createEffect,
 } from "solid-js";
 
-import { generateKey, encrypt } from "../lib/crypto";
+import { generateKey } from "../lib/crypto";
 import { formatBytes } from "../lib/utils";
 
 const viewClass = "flex flex-col items-center gap-2 sm:gap-3";
@@ -51,6 +51,7 @@ export default function Upload() {
 
   let fileInput!: HTMLInputElement;
   let activeXhr: XMLHttpRequest | null = null;
+  let worker: Worker | null = null;
 
   const RADIUS = 130;
   const CENTER = RADIUS + 10;
@@ -135,6 +136,9 @@ export default function Upload() {
   };
 
   onMount(async () => {
+    worker = new Worker(new URL("../lib/crypto.worker.ts", import.meta.url), {
+      type: "module",
+    });
     document.addEventListener("dragover", handleDragOver);
     document.addEventListener("dragleave", handleDragLeave);
     document.addEventListener("drop", handleDrop);
@@ -157,6 +161,7 @@ export default function Upload() {
     document.removeEventListener("dragover", handleDragOver);
     document.removeEventListener("dragleave", handleDragLeave);
     document.removeEventListener("drop", handleDrop);
+    worker?.terminate();
   });
 
   const removeFile = () => {
@@ -185,9 +190,25 @@ export default function Upload() {
     setProgress(0);
 
     try {
-      const { key, encoded } = await generateKey();
+      const { encoded } = await generateKey();
       const buffer = await f.arrayBuffer();
-      const ciphertext = await encrypt(f.name || "file", buffer, key);
+      const ciphertext = await new Promise<Uint8Array<ArrayBuffer>>(
+        (resolve, reject) => {
+          worker!.onmessage = (e) => {
+            if (e.data.error) reject(new Error(e.data.error));
+            else resolve(e.data.ciphertext);
+          };
+          worker!.postMessage(
+            {
+              type: "encrypt",
+              fileName: f.name || "file",
+              fileBuffer: buffer,
+              keyEncoded: encoded,
+            },
+            [buffer],
+          );
+        },
+      );
 
       const formData = new FormData();
       formData.append("file", new Blob([ciphertext]));
diff --git a/web/src/pages/View.tsx b/web/src/pages/View.tsx
index 6dc4570..8af7646 100644
--- a/web/src/pages/View.tsx
+++ b/web/src/pages/View.tsx
@@ -1,7 +1,14 @@
 import { useParams } from "@solidjs/router";
-import { createSignal, Show, Switch, Match, onMount } from "solid-js";
+import {
+  createSignal,
+  Show,
+  Switch,
+  Match,
+  onMount,
+  onCleanup,
+} from "solid-js";
 
-import { importKey, decrypt } from "../lib/crypto";
+import { importKey } from "../lib/crypto";
 import {
   formatBytes,
   formatExpiry,
@@ -34,7 +41,13 @@ export default function View() {
   const [fileName, setFileName] = createSignal("");
 
   let decryptedBlob: Blob | null = null;
-  let cryptoKey: CryptoKey;
+  const worker = new Worker(
+    new URL("../lib/crypto.worker.ts", import.meta.url),
+    {
+      type: "module",
+    },
+  );
+  onCleanup(() => worker.terminate());
 
   onMount(async () => {
     const id = params.id;
@@ -47,7 +60,7 @@ export default function View() {
     }
 
     try {
-      cryptoKey = await importKey(keyEncoded);
+      await importKey(keyEncoded);
     } catch {
       setError("Invalid key.");
       setStage("error");
@@ -81,10 +94,23 @@ export default function View() {
       }
 
       const buf = await res.arrayBuffer();
-      const { fileName: name, fileData } = await decrypt(
-        new Uint8Array(buf),
-        cryptoKey,
-      );
+      const { fileName: name, fileData } = await new Promise<{
+        fileName: string;
+        fileData: Uint8Array<ArrayBuffer>;
+      }>((resolve, reject) => {
+        worker.onmessage = (e) => {
+          if (e.data.error) reject(new Error(e.data.error));
+          else resolve(e.data);
+        };
+        worker.postMessage(
+          {
+            type: "decrypt",
+            ciphertext: buf,
+            keyEncoded: location.hash.slice(1),
+          },
+          [buf],
+        );
+      });
       const ext = getExt(name);
       setFileName(name);