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apps/desktop/src/lib/cryptoBackend.ts

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+import type { CryptoBackend } from '@chat-app/shared/crypto';
+import _sodium from 'libsodium-wrappers';
+
+// Build the libsodium-backed CryptoBackend. Awaits the WASM ready-gate once,
+// then returns a synchronous implementation of the CryptoBackend contract.
+export async function createLibsodiumBackend(): Promise<CryptoBackend> {
+  await _sodium.ready;
+  const s = _sodium;
+
+  return {
+    name: 'libsodium-wrappers',
+    nonceLength: s.crypto_box_NONCEBYTES,
+    publicKeyLength: s.crypto_box_PUBLICKEYBYTES,
+    privateKeyLength: s.crypto_box_SECRETKEYBYTES,
+    secretboxKeyLength: s.crypto_secretbox_KEYBYTES,
+    secretboxNonceLength: s.crypto_secretbox_NONCEBYTES,
+    randomBytes: (n: number) => s.randombytes_buf(n),
+    generateKeyPair: () => {
+      const kp = s.crypto_box_keypair();
+      return { publicKey: kp.publicKey, privateKey: kp.privateKey };
+    },
+    box: (plaintext, nonce, recipientPublicKey, senderPrivateKey) =>
+      s.crypto_box_easy(plaintext, nonce, recipientPublicKey, senderPrivateKey),
+    boxOpen: (ciphertext, nonce, senderPublicKey, recipientPrivateKey) =>
+      s.crypto_box_open_easy(ciphertext, nonce, senderPublicKey, recipientPrivateKey),
+    secretbox: (plaintext, nonce, key) => s.crypto_secretbox_easy(plaintext, nonce, key),
+    secretboxOpen: (ciphertext, nonce, key) => s.crypto_secretbox_open_easy(ciphertext, nonce, key),
+  };
+}