From 2463081949df388e388f0144643557b332be73fe Mon Sep 17 00:00:00 2001
From: byGalax <dennis@landmann.dev>
Date: Sat, 16 May 2026 16:30:52 +0200
Subject: [PATCH] feat(shared): extend CryptoBackend with pwhash +
 scalarMultBase

---
 .../src/crypto/backend.contract.test.ts       | 43 +++++++++++++++++++
 packages/shared/src/crypto/backend.ts         | 24 +++++++++++
 packages/shared/src/crypto/testBackend.ts     |  8 ++++
 3 files changed, 75 insertions(+)
 create mode 100644 packages/shared/src/crypto/backend.contract.test.ts

diff --git a/packages/shared/src/crypto/backend.contract.test.ts b/packages/shared/src/crypto/backend.contract.test.ts
new file mode 100644
index 0000000..cdc993d
--- /dev/null
+++ b/packages/shared/src/crypto/backend.contract.test.ts
@@ -0,0 +1,43 @@
+import { describe, expect, it } from 'vitest';
+
+import type { CryptoBackend } from './backend';
+import { makeWasmTestBackend } from './testBackend';
+
+describe('CryptoBackend contract — extended (pwhash + scalarMultBase)', () => {
+  it('pwhashConsts exposes the constants userKey.ts needs', async () => {
+    const backend: CryptoBackend = await makeWasmTestBackend();
+    expect(backend.pwhashConsts.OPSLIMIT_MODERATE).toBeGreaterThan(0);
+    expect(backend.pwhashConsts.MEMLIMIT_MODERATE).toBeGreaterThan(0);
+    expect(backend.pwhashConsts.ALG_ARGON2ID13).toBeGreaterThan(0);
+  });
+
+  it('pwhash is deterministic for fixed input + salt', async () => {
+    const backend: CryptoBackend = await makeWasmTestBackend();
+    const salt = new Uint8Array(16).fill(7);
+    const a = backend.pwhash(
+      32,
+      'hunter2',
+      salt,
+      backend.pwhashConsts.OPSLIMIT_MODERATE,
+      backend.pwhashConsts.MEMLIMIT_MODERATE,
+      backend.pwhashConsts.ALG_ARGON2ID13,
+    );
+    const b = backend.pwhash(
+      32,
+      'hunter2',
+      salt,
+      backend.pwhashConsts.OPSLIMIT_MODERATE,
+      backend.pwhashConsts.MEMLIMIT_MODERATE,
+      backend.pwhashConsts.ALG_ARGON2ID13,
+    );
+    expect(a).toEqual(b);
+    expect(a.length).toBe(32);
+  });
+
+  it('scalarMultBase maps the private key of a generated keypair to its public key', async () => {
+    const backend: CryptoBackend = await makeWasmTestBackend();
+    const kp = backend.generateKeyPair();
+    const derived = backend.scalarMultBase(kp.privateKey);
+    expect(derived).toEqual(kp.publicKey);
+  });
+});
diff --git a/packages/shared/src/crypto/backend.ts b/packages/shared/src/crypto/backend.ts
index 39ae1da..22fcc2f 100644
--- a/packages/shared/src/crypto/backend.ts
+++ b/packages/shared/src/crypto/backend.ts
@@ -47,6 +47,30 @@ export interface CryptoBackend {
   // distributed per recipient via crypto_box envelopes.
   secretbox(plaintext: Uint8Array, nonce: Uint8Array, key: Uint8Array): Uint8Array;
   secretboxOpen(ciphertext: Uint8Array, nonce: Uint8Array, key: Uint8Array): Uint8Array;
+
+  // ---------------------------------------------------------------------
+  // Key derivation + public-key derivation. Added so the user-key flow
+  // (Argon2id KDF, scalarmult-base for public-key derivation from a cached
+  // private key) does not have to import libsodium-wrappers-sumo at module
+  // top level — that import does not load in React Native's Hermes runtime.
+  // ---------------------------------------------------------------------
+
+  readonly pwhashConsts: {
+    OPSLIMIT_MODERATE: number;
+    MEMLIMIT_MODERATE: number;
+    ALG_ARGON2ID13: number;
+  };
+
+  pwhash(
+    outLen: number,
+    password: string,
+    salt: Uint8Array,
+    opslimit: number,
+    memlimit: number,
+    alg: number,
+  ): Uint8Array;
+
+  scalarMultBase(privateKey: Uint8Array): Uint8Array;
 }
 
 let current: CryptoBackend | null = null;
diff --git a/packages/shared/src/crypto/testBackend.ts b/packages/shared/src/crypto/testBackend.ts
index d5f88c0..d84eb33 100644
--- a/packages/shared/src/crypto/testBackend.ts
+++ b/packages/shared/src/crypto/testBackend.ts
@@ -22,5 +22,13 @@ export async function makeWasmTestBackend(): Promise<CryptoBackend> {
     boxOpen: (c, n, pk, sk) => sodium.crypto_box_open_easy(c, n, pk, sk),
     secretbox: (m, n, k) => sodium.crypto_secretbox_easy(m, n, k),
     secretboxOpen: (c, n, k) => sodium.crypto_secretbox_open_easy(c, n, k),
+    pwhashConsts: {
+      OPSLIMIT_MODERATE: sodium.crypto_pwhash_OPSLIMIT_MODERATE,
+      MEMLIMIT_MODERATE: sodium.crypto_pwhash_MEMLIMIT_MODERATE,
+      ALG_ARGON2ID13: sodium.crypto_pwhash_ALG_ARGON2ID13,
+    },
+    pwhash: (outLen, password, salt, opslimit, memlimit, alg) =>
+      sodium.crypto_pwhash(outLen, password, salt, opslimit, memlimit, alg),
+    scalarMultBase: (priv) => sodium.crypto_scalarmult_base(priv),
   };
 }