diff --git a/web/utils/aes-crypto.js b/web/utils/aes-crypto.js
new file mode 100644
--- /dev/null
+++ b/web/utils/aes-crypto.js
@@ -0,0 +1,70 @@
+// @flow
+
+const KEY_SIZE = 32; // bytes
+const IV_LENGTH = 12; // bytes
+const TAG_LENGTH = 16; // bytes
+
+async function generateKey(): Promise<Uint8Array> {
+  const algorithm = { name: 'AES-GCM', length: 256 };
+  const key = await crypto.subtle.generateKey(algorithm, true, [
+    'encrypt',
+    'decrypt',
+  ]);
+  const keyData = await crypto.subtle.exportKey('raw', key);
+  return new Uint8Array(keyData);
+}
+
+async function encrypt(
+  keyBytes: Uint8Array,
+  plaintext: Uint8Array,
+): Promise<Uint8Array> {
+  if (keyBytes.length !== KEY_SIZE) {
+    throw new Error('Invalid AES key size');
+  }
+
+  // we're creating the buffer now so we can avoid reallocating it later
+  const outputBuffer = new ArrayBuffer(
+    plaintext.length + IV_LENGTH + TAG_LENGTH,
+  );
+  const ivBytes = new Uint8Array(outputBuffer, 0, IV_LENGTH);
+  const iv = crypto.getRandomValues(ivBytes);
+
+  const algorithm = { name: 'AES-GCM', iv: iv, tagLength: TAG_LENGTH * 8 };
+  const key = await crypto.subtle.importKey('raw', keyBytes, 'AES-GCM', false, [
+    'encrypt',
+  ]);
+  const ciphertext = await crypto.subtle.encrypt(algorithm, key, plaintext);
+
+  const result = new Uint8Array(outputBuffer);
+  result.set(new Uint8Array(ciphertext), iv.length);
+  return result;
+}
+
+async function decrypt(
+  keyBytes: Uint8Array,
+  ciphertextData: Uint8Array,
+): Promise<Uint8Array> {
+  if (keyBytes.length !== KEY_SIZE) {
+    throw new Error('Invalid AES key size');
+  }
+  if (ciphertextData.length < IV_LENGTH + TAG_LENGTH) {
+    throw new Error('Invalid ciphertext');
+  }
+
+  const iv = ciphertextData.subarray(0, IV_LENGTH);
+  const ciphertextContent = ciphertextData.subarray(IV_LENGTH);
+
+  const algorithm = { name: 'AES-GCM', iv, tagLength: TAG_LENGTH * 8 };
+  const key = await crypto.subtle.importKey('raw', keyBytes, 'AES-GCM', false, [
+    'decrypt',
+  ]);
+
+  const plaintextBuffer = await crypto.subtle.decrypt(
+    algorithm,
+    key,
+    ciphertextContent,
+  );
+  return new Uint8Array(plaintextBuffer);
+}
+
+export { generateKey, encrypt, decrypt };