diff --git a/packages/shared/src/crypto/userKey.ts b/packages/shared/src/crypto/userKey.ts
index 67b3fa7..a9394a3 100644
--- a/packages/shared/src/crypto/userKey.ts
+++ b/packages/shared/src/crypto/userKey.ts
@@ -1,5 +1,3 @@
-import sodium from 'libsodium-wrappers-sumo';
-
 import { getCryptoBackend } from './backend';
 import type { KeyPair } from './backend';
 
@@ -23,24 +21,25 @@ export async function generateUserKeyPair(): Promise<KeyPair> {
   return getCryptoBackend().generateKeyPair();
 }
 
-async function deriveKek(pin: string, salt: Uint8Array, params: KdfParams): Promise<Uint8Array> {
-  await sodium.ready;
-  return sodium.crypto_pwhash(
-    sodium.crypto_secretbox_KEYBYTES,
+function deriveKek(pin: string, salt: Uint8Array, params: KdfParams): Uint8Array {
+  const backend = getCryptoBackend();
+  return backend.pwhash(
+    backend.secretboxKeyLength,
     pin,
     salt,
     params.opslimit,
     params.memlimit,
-    sodium.crypto_pwhash_ALG_ARGON2ID13,
+    backend.pwhashConsts.ALG_ARGON2ID13,
   );
 }
 
 function defaultKdfParams(): KdfParams {
+  const backend = getCryptoBackend();
   return {
     algo: 'argon2id',
     preset: KDF_PRESET,
-    opslimit: sodium.crypto_pwhash_OPSLIMIT_MODERATE,
-    memlimit: sodium.crypto_pwhash_MEMLIMIT_MODERATE,
+    opslimit: backend.pwhashConsts.OPSLIMIT_MODERATE,
+    memlimit: backend.pwhashConsts.MEMLIMIT_MODERATE,
   };
 }
 
@@ -50,19 +49,16 @@ export async function sealUserKey(opts: {
   salt?: Uint8Array;
   kdfParams?: KdfParams;
 }): Promise<SealedUserKey> {
-  await sodium.ready;
   const backend = getCryptoBackend();
   const salt = opts.salt ?? backend.randomBytes(SALT_LEN);
   const kdfParams = opts.kdfParams ?? defaultKdfParams();
-  const kek = await deriveKek(opts.pin, salt, kdfParams);
-  try {
-    const nonce = backend.randomBytes(backend.secretboxNonceLength);
-    const cipher = backend.secretbox(opts.privateKey, nonce, kek);
-    const sealedPrivateKey = new Uint8Array(nonce.length + cipher.length);
-    sealedPrivateKey.set(nonce, 0);
-    sealedPrivateKey.set(cipher, nonce.length);
-    return { sealedPrivateKey, salt, kdfParams };
-  } finally { sodium.memzero(kek); }
+  const kek = deriveKek(opts.pin, salt, kdfParams);
+  const nonce = backend.randomBytes(backend.secretboxNonceLength);
+  const cipher = backend.secretbox(opts.privateKey, nonce, kek);
+  const sealedPrivateKey = new Uint8Array(nonce.length + cipher.length);
+  sealedPrivateKey.set(nonce, 0);
+  sealedPrivateKey.set(cipher, nonce.length);
+  return { sealedPrivateKey, salt, kdfParams };
 }
 
 export async function openUserKey(opts: {
@@ -71,12 +67,11 @@ export async function openUserKey(opts: {
   salt: Uint8Array;
   kdfParams: KdfParams;
 }): Promise<Uint8Array> {
-  await sodium.ready;
   const backend = getCryptoBackend();
   const nonceLen = backend.secretboxNonceLength;
   if (opts.sealed.length <= nonceLen) throw new Error('sealed user key blob too short');
   const nonce = opts.sealed.slice(0, nonceLen);
   const cipher = opts.sealed.slice(nonceLen);
-  const kek = await deriveKek(opts.pin, opts.salt, opts.kdfParams);
-  try { return backend.secretboxOpen(cipher, nonce, kek); } finally { sodium.memzero(kek); }
+  const kek = deriveKek(opts.pin, opts.salt, opts.kdfParams);
+  return backend.secretboxOpen(cipher, nonce, kek);
 }