Implement Native Scalar Multiplication

README.md

@@ -84,6 +84,7 @@ import {
   crypto_sign_keypair,
   crypto_sign_SEEDBYTES,
   crypto_sign_verify_detached,
+  crypto_scalarmult,
   from_base64,
   randombytes_buf,
   randombytes_uniform,

cpp/react-native-libsodium.cpp

@@ -1539,5 +1539,43 @@ namespace ReactNativeLibsodium
             });
 
         jsiRuntime.global().setProperty(jsiRuntime, "jsi_crypto_kdf_hkdf_sha256_expand", std::move(jsi_crypto_kdf_hkdf_sha256_expand));
+
+        auto jsi_crypto_scalarmult = jsi::Function::createFromHostFunction(
+            jsiRuntime,
+            jsi::PropNameID::forUtf8(jsiRuntime, "jsi_crypto_scalarmult"),
+            3,
+            [](jsi::Runtime &runtime, const jsi::Value &thisValue, const jsi::Value *arguments, size_t count) -> jsi::Value
+            {
+                const std::string functionName = "crypto_scalarmult";
+
+                std::string privateKeyArgumentName = "privateKey";
+                unsigned int privateKeyArgumentPosition = 0;
+                validateIsArrayBuffer(functionName, runtime, arguments[privateKeyArgumentPosition], privateKeyArgumentName, true);
+
+                std::string publicKeyArgumentName = "publicKey";
+                unsigned int publicKeyArgumentPosition = 1;
+                validateIsArrayBuffer(functionName, runtime, arguments[publicKeyArgumentPosition], publicKeyArgumentName, true);
+
+                auto privateKey = arguments[privateKeyArgumentPosition].asObject(runtime).getArrayBuffer(runtime);
+                auto publicKey = arguments[publicKeyArgumentPosition].asObject(runtime).getArrayBuffer(runtime);
+
+                if (privateKey.length(runtime) != crypto_secretbox_KEYBYTES)
+                {
+                    throw jsi::JSError(runtime, "invalid private key length");
+                }
+                if (publicKey.length(runtime) != crypto_secretbox_KEYBYTES)
+                {
+                    throw jsi::JSError(runtime, "invalid public key length");
+                }
+
+                std::vector<uint8_t> result;
+                result.resize(crypto_scalarmult_BYTES);
+
+                crypto_scalarmult(result.data(), privateKey.data(runtime), publicKey.data(runtime));
+
+                return arrayBufferAsObject(runtime, result);
+            });
+
+        jsiRuntime.global().setProperty(jsiRuntime, "jsi_crypto_scalarmult", std::move(jsi_crypto_scalarmult));
     }
 } // namespace ReactNativeLibsodium

src/lib.native.ts

@@ -173,6 +173,10 @@ declare global {
     info: string,
     length: number
   ): ArrayBuffer;
+  function jsi_crypto_scalarmult(
+    privateKey: ArrayBuffer,
+    publicKey: ArrayBuffer
+  ): ArrayBuffer;
 }
 
 export const crypto_auth_BYTES = global.jsi_crypto_auth_BYTES;
@@ -795,6 +799,20 @@ export function _unstable_crypto_kdf_hkdf_sha256_expand(
   );
 }
 
+export function crypto_scalarmult(
+  privateKey: Uint8Array,
+  publicKey: Uint8Array,
+  outputFormat?: Uint8ArrayOutputFormat | null,
+) {
+  let result: ArrayBuffer;
+  result = global.jsi_crypto_scalarmult(
+    privateKey.buffer,
+    publicKey.buffer,
+  );
+
+  return convertToOutputFormat(result, outputFormat);
+}
+
 // add no-op ready to match the libsodium-wrappers API
 export const ready: Promise<void> = new Promise((resolve) => resolve());
 
@@ -844,6 +862,7 @@ export default {
   crypto_sign_detached,
   crypto_sign_keypair,
   crypto_sign_verify_detached,
+  crypto_scalarmult,
   from_base64,
   randombytes_buf,
   randombytes_uniform,